Antibacterial and antifungal compounds from marine fungi.

This paper reviews 116 new compounds with antifungal or antibacterial activities as well as 169 other known antimicrobial compounds, with a specific focus on January 2010 through March 2015. Furthermore, the phylogeny of the fungi producing these antibacterial or antifungal compounds was analyzed. The new methods used to isolate marine fungi that possess antibacterial or antifungal activities as well as the relationship between structure and activity are shown in this review.

1. Introduction

Antibacterials and antifungals are among the most commonly used drugs. Recn class="Chemical">ently, as the resistance of bacterial and fungal pathogens has become increasingly serious, there is a growing demand for new antibacterial and antifungal compounds. Natural products from fungi are considered an important source for novel antibacterial and antifungal compounds because of their abundant fungal species diversity, their rich secondary metabolites and the improvements in their genetic breeding and fermentation processes. The antimicrobial activities of an increasing number of fungi living in distinctive environments are being investigated for the discovery of new antibacterial and antifungal compounds, such as endophytic fungi from wild plants and marine fungi. In the last decade, many novel bioactive natural products from marine fungi have been discovered that possess cytotoxic, anticancer, antiviral, antibacterial or antifungal activities [1,2,3,4,5,6]. The antibacterial and antifungal compounds from marine fungi have quickly increased since 2010, and marine fungi have been an important source of antibacterial and antifungal compounds. This paper reviews the antibacterial and antifungal compounds from marine fungi with specific focus on the period from January 2010 to March 2015.

2. Sampling Location

Marine fungi are an ecologically rather than physiologically or taxonomically defined group of organisms [1]. Marine fungi are parasitic or saprophytic in other marine organisms or materials. We collected 117 peer-reviewed research articles regarding antibacterial or antifungal compounds from marine fungi from January 2010 to March 2015. Most of the sites shown in Figure 1 are approximate locations n class="Chemical">based on the information about the marine material samplings in the literature and the other sites plotted by their exact latitude and longitude (details shown in Supplementary Table S1). There are 17 literature reports without collection locale information, and they are not included in Figure 1. According to Figure 1, most of the materials for fungal isolation were obtained near the coastal area of Eurasia, and more than a half of the marine materials are from the coastal area near China. Many natural products are used as medicines in China, and the Chinese people are traditionally keen on the discovery and development of natural medicines.

Figure 1

The approximate location of material collections for fungal isolation.

3. Fungal Isolation and Identification

Many different types of marine materials were collected for the fungal isolations. According to the literature, there are 105 marine fungal strains used for the isolation of antin class="Chemical">bacterial or antifungal compounds. These 105 marine fungal strains were isolated from marine materials, which are divided into 12 classes as shown in Figure 2.

Figure 2

Numbers of fungal strains from different isolation materials.

Numn class="Chemical">bers of fungal strains from different isolation materials.

Algae, sponges and mangroves are the most common materials for the isolation of fungal strains that can produce antin class="Chemical">bacterial or antifungal compounds. The fungi associated with these algae, sponges and mangroves are expected to produce compounds with novel or special skeletons because of the special interactions between the fungi and the algae, sponges or mangroves. Additionally, 20 of the 116 new compounds with antifungal or antibacterial activities are from the 11 fungal strains from marine sediments, indicating that these sediments are also good materials for the isolation of fungi. Therefore, based on the data from the past five years for the number of new compounds with antifungal or antibacterial activities, fungi isolated from sediments seem to be underestimated and fungi from sponges may be overestimated (21 new compounds with antibacterial and antifungal activities from 19 fungal strains from sponges). The information about the sampling sites, fungal sources and taxonomic names are shown in the Supplemental Material.

Over 700 compounds in total were purified from 105 fungal strains that can produce antimicrobial compounds and were investigated for these activities. There are 285 compounds (approximately 40% of the total) that showed antin class="Chemical">bacterial or antifungal activities and 116 (15% of the total) are new antibacterial and antifungal compounds. On average, more than one new compound with antibacterial and antifungal activities could be isolated from one fungal strain. According to the antimicrobial screening of marine fungal extracts from four literature reports [7,8,9,10], 38%–59% of the test extracts from marine fungi exhibited antibacterial or antifungal activities. Taken together, these data indicate that marine fungi are a good source of natural antibacterial and antifungal compounds.

Most of the 105 marine fungi with antibacterial or antifungal compounds were idn class="Chemical">entified, and approximately 50% of them were identified based on their DNA sequence. The dominant genera in the marine fungi producing antibacterial and antimicrobial compounds were the Aspergillus genus (31 strains) and the Penicillium genus (16 strains).

4. Phylogenetic Analysis

To obtain an overview of the phylogenetic relationship among the marine fungi that produce antibacterial or antifungal compounds, we analyzed the internal transcribed spacer (ITS) data sets of 41 sequences from marine fungi with antibacterial or antifungal activities. Originally, 49 fungal DNA sequences were collected from the 117 literature reports. Eight of these sequences were calmodulin, tubulin or 18S ribosomal RNA genes, and the rest were the 41 ITS sequences used for phylogeny analysis. The ITS sequences were aligned by ClustalW implemented in BIOEDIT ver. 7.0.5 [11], and optimized manually using BIOEDIT. Maximum likelihood (ML) analysis was constructed using the Kimura 2-parameter (K2) nucleotide substitutions model as selected by MEGA6 [12]. A ML tree was generated using MEGA6 with bootstrap values calculated from 100 replicates (Figure 3). The phylogenetic tree was rooted with the Mucor mucedo ITS sequence (shown in Figure 3).

Figure 3

Phylogenetic analysis of marine fungi produced antibacterial or antifungal compounds.

In the data from the last five years (January 2010 to March 2015), the marine fungi producing antibacterial or antifungal compounds did not display as high of a diversity as expected. All sampled marine fungi came from Ascomycota and were limited to Eurotiomycetes, Dothideomycetes, and Sordariomycetes. Most fungi n class="Chemical">belonged to the Eurotiomycetes, forming a well-supported clade (Figure 3: BS = 100%). Compared with the Sordariomycetes, the Dothideomycetes and Eurotiomycetes were similar to each other with weak support (Figure 3: BS = 53%). Although the Diaporthales, Hypocreales, Xylariales, and Trichosphaeriales are from the same class, they diverged into two distinct clades. Diaporthales and Hypocreales appeared to form a moderately supported clade (Figure 3: BS = 79%).

Of the new compounds with antibacterial or antifungal activities purified from these 41 fungal strains, 51 were also listed in Figure 3. According to Figure 3, the fungal strains from Aspergillacea produced 31 of the n class="Chemical">polyketides (including the N-containing polyketides) and 6 of the steroids and terpenoids. Therefore, it is possible that the main antibacterial and antifungal compounds of the marine fungal strains are from Aspergillacea are polyketides, but beyond that, it is difficult to find a correlation between the types of new compounds and the phylogeny of the marine fungi. However, it is interesting to note that the quantity of new antibacterial and antifungal compounds may be related to the phylogeny of the marine fungi. Moreover, none of the new antibacterial or antifungal compounds purified were from Pleosporales. However, the 20 fungal strains from the four phylogenic groups highlighted in red in Figure 3 produced over 80% of the new antibacterial and antifungal compounds. New antibacterial and antifungal compounds were purified from all five strains from Hypocreales. Two Aspergillus spp. (of the three total Aspergillus spp.) and one Penicillium sp. (of five) were also good sources for new antibacterial and antifungal compounds. Therefore, the marine fungal strains from Hypocreales and the Aspergillus and Penicillium genera should be utilized more for the discovery of new antibacterial or antifungal compounds.

Phylogenetic analysis of marine fungi produced antin class="Chemical">bacterial or antifungal compounds.

5. New Antibacterial and Antifungal Compounds from Marine Fungi

5.1. Nitrogen-Containing Compounds

5.1.1. Peptides

Cyclopeptides from terrestrial microorganisms are considered a good antimicron class="Chemical">bial source. However, only six new antimicrobial cyclopeptides, 1–6 (Figure 4), were isolated from three marine fungi. Two cyclotetrapeptides (d-Pro-l-Tyr-l-Pro-l-Tyr) (1) and (Gly-l-Phe-l-Pro-l-Tyr) (2), were isolated from the co-culture broth of mangrove fungi Phomopsis sp. K38 and Alternaria sp. E33 [13]. Compound 2 showed stronger activity (MIC, 25–250 μg/mL) than 1 (35–400 μg/mL) against five tested fungi. Cyclopentapeptide lajollamide A (3) was isolated from Asteromyces cruciatus 763. Natural lajollamide A (3), which is a mixture of several stereochemical configurations, has only weak antibacterial activity against Bacillus subtilis and Staphylococcus epidermidis [14]. However, the absolute configuration of lajollamide A (3) (leucine residues 1–3: d-Leu-l-Leu-l-Leu), which was solved by total synthesis, was more active than natural lajollamide A (3). This indicates that the diastereomers of the Leu-Leu-Leu moiety effectively impact the antibacterial activity. Isaridin G (4), desmethylisaridin G (5) and desmethylisaridin C1 (6) are three new cyclohexadepsipeptides of the isaridin class that were isloated from Beauveria felina EN-135. These compounds showed inhibitory activity against Escherichia coli (MIC, 64, 64 and 8 μg/mL, respectively) and this is the first report of antibacterial activity of the isaridins [15].

Figure 4

Structures of compound 1–6.

5.1.2. Indole-Alkaloids

Ten new n class="Chemical">indole-alkaloids, 7–12 and 14–17 (Figure 5 and Figure 6), showed antibacterial activities and most were isolated from marine fungi belonging to Aspergillus and Penicillium genera. The 4-hydroxy-4-methylpent-2-enyl moiety (red group shown in the chemical structure of 7) in asporyzin C (7), which was isolated from A. oryzae was deduced to be necessary for antibacterial activity against E. coli [16]. Compound 8 was isolated from A. flavus OUCMDZ-2205, which exhibited stronger activity against Staphylococcus aureus (MIC, 20.5 μM) than did the known analog, β-aflatrem from the same fungal strain [17]. Cristatumins A (9), D (10) and E (11) were isolated from Eurotium cristatum EN-220 (9 and 10) and E. herbariorum HT-2 (Eurotium sp. is sexual state of Aspergillus sp.) [18,19]. These three compounds displayed bacterial inhibitory activity. Cristatumin A (9) exhibited activity against E. coli and S. aureus (MIC, 64 μg/mL) and cristatumin D (10) showed weak activity against S. aureus with an inhibition zone (IZ) of 8 mm at 100 μg/disk. Cristatumin E (11) exhibited antibacterial activity against Enterobacter aerogenes and E. coli (MIC, 44.0 and 44.0 μM, respectively). By comparison to known compound neoechinulin A, the antibacterial activity of 9 appears related to the hydroxyl moiety on C-20. Compound 12 was also isolated from an Aspergillus sp. and exhibited potent activity against Vibrio spp. (MIC, 0.1 and 1 μg/mL) [20]. Diaporthalasin (13), which was isolated from Diaporthaceae sp. PSU-SP2/4, displayed significant antibacterial activity against both S. aureus and methicillin-resistant S. aureus (MRSA) with equal MIC values of 2 μg/mL [21].

Figure 5

Structures of compound 7–13 (the red moiety enhances the antimicrobial activity).

Figure 6

Structures of compound 14–18 (the red moiety enhances the antimicrobial activity).

Structures of compound 7–13 (the red moiety enhances the antimicron class="Chemical">bial activity).

Penicibrocazines n class="Chemical">B–E (14–17) (Figure 6) were produced by P. brocae MA-231. Compounds 14–16 showed antibacterial activity against S. aureus (MIC, 32.0, 0.25 and 8.0 μg/mL, respectively) and compounds 14, 16 and 17 showed antifungal activity against Gaeumannomyces graminis (MIC, 0.25, 8.0 and 0.25 μg/mL, respectively). By comparison with the known compound Penicibrocazine A lacking antimicrobial activity, the double bonds at C-6 and C-6′ increased activity against S. aureus and more S-methyl groups likely strengthened activity against G. graminis. In addition, the keto groups at C-5/5′ enhanced the activity against G. graminis [22]. Stachyin B (18) was isolated from Stachybotrys sp. MF347 and showed activity against three Gram-positive bacterial strains MRSA, B. subtilis and S. epidermidis (IC50, 1.75, 1.42 and 1.02 μM, respectively) but no activity against the Gram-negative test strain and the fungal strains. Stachyin B (18) is the first dimeric spirodihydrobenzofuranlactams with N–C linkage (red color shown in the below structure) and its analogs (the other dimeric spirodihydrobenzofuranlactams) are N–N linkage instead. This N–C linkage is important for its antibacterial activity, as determined by comparison of the activity of stachyin B (18) with other N–N connected analogs (other dimeric spirodihydrobenzofuranlactams) and stachyin A (a single spirodihydrobenzofuranlactam) [23].

Structures of compound 14–18 (the red moiety enhances the antimicron class="Chemical">bial activity).

5.1.3. Pyridines and Pyridinones

The structures of compound 19–23 were shown in Figure 7. Trichodin A (19) was isolated from n class="Species">Trichoderma sp. MF106 and showed antibacterial activity against Gram-positive B. subtilis and S. epidermidis (IC50, 27.05 and 24.28 µM, respectively) and antifungal activity against Candida albicans (IC50, 25.38 μM) [24]. However, trichodin B, which substituted a ribofuranose group for the C-20 hydroxyl of 19, showed no activity against any test microorganisms. Compound 20 was isolated from Wallemia sebi PXP-89 and was elucidated to be 5,6-dihydro-3-hydroxy-5-methylcyclopenta[b]pyridin-7-one with weak antibacterial activity against E. aerogenes (MIC, 76.7 µM) [25]. Didymellamides A (21) and B (22) were isolated from Stagonosporopsis cucurbitacearum. Didymellamide A (21) inhibited three strains of Candida spp. (MIC, 3.1 μg/mL) and Cryptococcus neoformans (MIC, 1.6 μg/mL). Didymellamide B (22) only inhibited C. neoformans (MIC, of 6.3 μg/mL) [26]. Curvulamine (23) was isolated from Curvularia sp. IFB-Z10 as a compound with a novel carbon skeleton and showed antibacterial activity against Veillonella parvula, Streptococcus sp. Bacteroides vulgatus and Peptostreptococcus sp. with an MIC value of 0.37 μM for all species. Curvulamine (23) has more selective antibacterial activity than tinidazole and is biosynthetically unique with a new extension formed through a decarboxylative condensation between an oligoketide motif and an alanine [27].

Figure 7

Structures of compound 19–23 (the red moiety enhances the antimicrobial activity).

Structures of compound 19–23 (the red moiety enhances the antimicron class="Chemical">bial activity).

5.1.4. Piperazine/Diketopiperazine and Pyrimidine/Pyrimidinone

The structures of compound 24–30 were shown in Figure 8. Aspergicin (24) was isolated from the co-culture of n class="Species">Aspergillus sp. FSY-01 and Aspergillus sp. FSW-02 and exhibited moderate antibacterial activity against S. aureus (MIC, 62.50 μg/mL), S. epidermidis (MIC, 31.25 μg/mL), B. subtilis (MIC, 15.62 μg/mL), B. dysenteriae (MIC, 15.62 μg/mL), B. proteus (MIC, 62.50 μg/mL) and E.coli (MIC, 31.25 MIC μg/mL) [28]. Terremides B (25), a pyrimidinone derivative, was isolated from A. terreus PT06-2 and showed weak activity against E. aerogenes (MIC, 33.5 μM) [29]. Two aroyl uridine derivatives kipukasins H (26) and I (27), were isolated from A. versicolorstrain ATCC 9577 and exhibited antibacterial activity against S. epidermidis (MIC, 12.5 μM). Their methylated derivatives (methoxyl substituted for C-4″ hydroxyl) were inactive against the test bacterial strain, which indicated that the hydroxyl at C-4″ may have a positive contribution to the antibacterial activity [30]. Pinodiketopiperazine A (28), a diketopiperazine derivative, was isolated from P. pinophilum SD-272 and displayed inhibitory activity against E. coli (IZ, 10 mm at 20 μg/disk) [31]. Two novel structural skeletons, compounds 29 and 30, were isolated from an Aspergillus sp. after screening over two thousand fungal strains. Waikialoid A (29) and waikialoid B (30) demonstrated dose-dependent activity in the biofilm inhibition assay against C. albicans with IC50 values of 1.4 and 46.3 μM, respectively. Although waikialoid A (29) was unable to disrupt preformed biofilms, by microscopy studies, it inhibited cell adherence, hyphal development, and biofilm assemblies during the early stages of surface colonization, and it was not cytotoxic to human cells [32].

Figure 8

Structures of compound 24–30 (the red moiety enhances the antimicrobial activity).

Structures of compound 24–30 (the red moiety enhances the antimicron class="Chemical">bial activity).

5.1.5. Other N-Containing Compounds

The structures of compound 31–39 were shown in Figure 9. Compound 31 was only produced by n class="Species">A. flocculosus PT05-1 under high salt stress conditions and showed antibacterial activity against E. aerogenes (MIC, 3.7 μM) [33]. Compound 32 was elucidated to be 4′-methoxyl-asperphenamate and was isolated from A. elegans ZJ-2008010. It showed a similar activity as asperphenamate against S. epidermis (MIC, 10 μM) [34]. Terremide A (33) was isolated from A. terreus PT06-2 and showed weak activity against S. aureus (MIC, 63.9 μM) [29]. Two cerebrosides, flavuside A (34) and flavuside B (35), were isolated from A. flavus. They exhibited 15.6 and 31.2 μg/mL MICs for S. aureus and MRSA [35]. Compound 36 was isolated from Paecilomyces sp. and exhibited weak activity against MRSA [36]. Trichoderin A (37), trichoderin A1 (38) and trichoderin B (39) were isolated from fungal strain 05FI48 and they exhibited potent antibacterial activity against M. smegmatis, M. bovis BBG and M. tuberculosis H37Rv (MIC, 0.1, 0.02 and 0.12 μg/mL for 37; 1.56, 0.16 and 2.0 μg/mL for 38; 0.63, 0.02 and 0.13 μg/mL for 39) [37,38]. Based on the comparison of the structures and activities of 37–39, the R1 hydroxyls (the red moiety shown in the structure 37 and 39) of 37 and 39 are related to their antibacterial activity. The mechanism of 37 was investigated using a transformant of M. smegmatis with resistance to 37. This M. smegmatis transformant over-expressed part of the genes that encoded the mycobacterial ATP synthase, indicating that the anti-mycobacterial activity of 37–39 is related to the inhibition of ATP synthesis.

Figure 9

Structures of compound 31–39 (the red moiety enhances the antimicrobial activity).

5.2. Steroids and Terpenoids

Three new steroids with antimicron class="Chemical">bial activity, 40–42 (Figure 10), were isolated from P. chrysogenum QEN-24S, A. ustus cf-42 and A. flocculosus PT05-1, respectively. Penicisteroid A (40) exhibited antifungal activity against A. niger and Alternaria brassicae (IZ, 24 mm and 16 at 20 μg/disk) [39]. The C-6 hydroxyl group may contribute to its activity, as determined by comparison with known compound anicequol (C-6 carbonyl group). Isocyathisterol (41) showed antibacterial activities against E. coli and S. aureus (IZ, 6.7 and 5.7 mm at 30 μg/disk, respectively) [40]. Compoud 42 was produced only under the high salinity conditions (10% salinity addition in fermentation) and exhibited antimicrobial activities against S. aureus, E. coli, and A. niger (MIC, 3.3, 3.3 and 1.6 μM, respectively) [33].

Figure 10

Structures of compound 40–42 (the red moiety enhances the antimicrobial activity).

Five new antimicrobial n class="Chemical">sesquiterpenoids, 43–47 (Figure 11), were isolated from Aspergillus sp. ZJ-2008004 (43–45), Leucostoma persoonii (46), Aspergillus sp. OPMF00272 (47) and Scyphiphora hydrophyllacea A1 (44). Aspergiterpenoid A (43), (−)-sydonol (44) and (−)-sydonic acid (45) showed activity against E. coli and Micrococcus tetragenus (MIC, 20 and 10 μM for 43; 20 and 1.25 μM for 44; and 5 and 20 μM for 45) [41]. Furthermore, compound 45 showed activity against other four test bacteria B. subtilis (MIC, 2.5 μM), Sarcina lutea (MIC, 2.5 μM), V. parahaemolyticus (MIC, 10 μM) and V. anguillarum (MIC, 5 μM), that 39 and 40 were inactive against. The C-4 carboxyl of 45 was important for the activtiy. Engyodontiumone I (46) displayed antibacterial activity against B. subtilis (MIC, 256.0 μg/mL) [42]. Terretonin G (47), a new meroterpene, showed activity against Gram-positive bacteria S. aureus, B. subtillis and M. luteus(IZ, 4, 2 and 2 mm at 20 μg/disk, respectively), but not against the Gram-negative test bacteria and fungi [43]. Guignardones I (48) (Figure 11), another new meroterpene, exhibited antibacterial activity toward MRSA and S. aureus (IZ, 3 and 5 mm at 1 µg/disk, respectively) [44].

Figure 11

Structures of compound 43–48 (the red moiety enhances the antimicrobial activity).

Structures of compound 31–39 (the red moiety enhances the antimicron class="Chemical">bial activity).

Structures of compound 40–42 (the red moiety enhances the antimicron class="Chemical">bial activity).

Structures of compound 43–48 (the red moiety enhances the antimicron class="Chemical">bial activity).

The structures of compound 49–52 were shown in Figure 12. Sesterterpene n class="Chemical">ophiobolin U (49) was isolated from fresh A. ustus cf-42 and exhibited inhibitory activities against E. coli and S. aureus (IZ, 15 and 10 mm at 30 μg/disk, respectively) [45]. Libertellenone G (50) was isolated from Eutypella sp. D-1 and showed antibacterial activity against E. coli, B. subtilis and S. aureus (IZ, 8, 8 and 9 at 50 μg/disk) [46]. Chevalone E (51) was isolated from A. similanensis sp. nov. KUFA 0013, which was found to show synergism with the antibiotic oxacillin against methicillin-resistant S. aureus (MRSA) [47]. Compound 52 was only produced by Nigrospora sp. MA75 in medium with 3.5% NaI and exhibited activity against MRSA (MIC, 8 µg/mL), E. coli (MIC, 4 μg/mL), P. aeruginosa (MIC, 4 µg/mL), P. fluorescens (MIC, 0.5 µg/mL) and S. epidermidis (MIC, 0.5 µg/mL), which implies that the added iodide ion may be triggering the activation of a mixed polyketide terpenoid biosynthetic pathway in this fungal strain [48].

Figure 12

Structures of compound 49–52.

5.3. Polyketides

5.3.1. Xanthones

The structures of compound 53–58 were shown in Figure 13. Six antimicrobial n class="Chemical">xanthones were isolated and their structures were elucidated. Engyodontiumone H (53) produced by Engyodontium album DFFSCS021 exhibited activity against E. coli (MIC, 64 µg/mL) and B. subtilis (MIC, 32 µg/mL) [42]. Compound 54 was isolated from the co-culture of unidentified strains E33 and K38 and exhibited activity against five flimantous fungal strains, Gloeasporium musae, Blumeria graminearum, Fusarium oxysporum, Perononphthora cichoralearum and Colletotrichum glocosporioides (respective inhibition rates of 53%, 4.6%, 9.5%, 48% and 28% at 100 µg/mL) [49,50]. Compound 55 was isolated from A. versicolor MF359 and showed significantly stronger activity against S. aureus (MIC, 12.5 μg/mL) and B. subtilis (MIC, 3.125 μg/mL) than 53 and 54 [51]. This difference implies that the two furan rings are most likely related to its antibacterial activity. Emerixanthones A (56), emerixanthone C (57) and emerixanthone D (58) isolated from Emericella sp. SCSIO 05240. Emerixanthones A (56) and emerixanthones C (57) exhibited antibacterial activity (IZ, 4–6 mm at 1.25 µg/disk) against all test bacteria E. coli, Klebsiella pneumonia, S. aureus, Enterococcus faecalis, Acineto bacterbaumannii and Aeromonas hydrophila. Emerixanthones D (58) showed an inhibitory zone of 3–4 mm against the fungal test phytopathogen Fusarium sp., Penicillium sp., A. niger, Rhizoctonia solani, F. oxysporium f. sp. niveum and F. sporium f. sp. cucumeris [52].

Figure 13

Structures of compound 53–58 (the red moiety enhances the antimicrobial activity).

Structures of compound 53–58 (the red moiety enhances the antimicron class="Chemical">bial activity).

5.3.2. Anthraquinones

The structures of compound 59–61 were shown in Figure 14. Trichodermaquinone (59) was isolated from n class="Species">T. aureoviride PSU-F95 and exhibited antibacterial activity against MRSA (MIC, 200 μg/mL). Compound 59 with a C-3 hydroxymethyl group (blue moiety in the structure of 59) showed significantly weaker activity than coniothranthraquinone, a known compound produced by the same fungal strain with a C-3 methyl group (red moiety in the structure of 59) (MIC, 8 μg/mL) [53]. Isorhodoptilometrin-1-methyl ether (60) was isolated from A. versicolor and exhibited antibacterial activity against three Gram-positive bacterial strains B. cereus, B. subtilis and S. aureus (IZ, 2, 3 and 5 mm at 50 µg/disk, respectively) [54]. The C-6 propanol group of 60 is important for its activity, as determined by comparison with inactive compound 1-methyl emodin. Compound 61 was isolated from A. versicolor EN-7 and exhibited antibacterial activity against E. coli (IZ, 7 mm at 20 μg/disk) [55].

Figure 14

Structures of compound 59–61 (the red moiety enhances the antimicrobial activity).

Structures of compound 59–61 (the red moiety enhances the antimicron class="Chemical">bial activity).

5.3.3. Quinones and Quinone Derivatives

The structures of compound 62–65 were shown in Figure 15. Anthraquinone derivatives, 62 and 63, were isolated from n class="Species">Nigrospora sp. No. 1403. Compound 62 exhibited potent activity against B. subtilis (MIC, 0.625), B. cereus (MIC, 10.0), M. luteus (MIC, 20.0 µM), S. albus (MIC, 5.00 µM), S. aureus (MIC, 2.50 µM), M. teragenus (MIC, 1.25 µM), E. coli (MIC, 2.50 µM), V. anguillarum (MIC, 2.50 µM) and V. parachemolyticus (MIC, 1.25 µM). Compound 63 was from the same fungal strain, but its antibacterial activity was significantly weaker than 62 [56]. From comparison of several known anthraquinone derivatives, the hydroxyl groups of 62 at C-4 and C-9 have little effect on the antibacterial activity but the hydroxyl group of 62 at C-3 most likely contributes to its antibacterial activity [56,57]. Seimatorone (64) was isolated from Seimatosporium sp. No. 8883 and showed antibacterial activity against E. coli and B. megaterium (IZ, 3 and 7 mm at 50 μg/disk, respectively) [58]. Trichodermaketone A (65) was from T. koningii and exhibited synergistic antifungal activity against C. albicans at 125 µg/mL with 0.05 µg/mL ketoconazole [59].

Figure 15

Structures of compound 62–65 (the red moiety enhances the antimicrobial activity).

The structures of compound 66–71 were shown in Figure 16. The structures of three new antimicrobial n class="Chemical">butenolides were elucidated from two Aspergillus spp. Spiculisporic acids B–D (66–68) were isolated from Aspergillus sp. HDf2 and exhibited a similar weak antibacterial activity against S. aureus [60]. Tubingenoic anhydride A (69), which was isolated from A. tubingensis OY907, inhibited Neurospora crassa growth (MIC, 330 μM) and affected hyphal morphology. Compound 69 may affect cell wall biosynthesis through a cytosolic protein that is the product of the new gene mas-1, originally characterized from the N. crassa mutant with tolerance to 69 [61]. Penicitide A (70) was purified from P. chrysogenum QEN-24S and displayed activity against A. brassicae (IZ, 6 mm at 20 μg/disk) [62]. Helicascolide C (71) was isolated from Daldinia eschscholzii KT32 and showed antifungal activity against phytopathogenic fungus Cladosporium cucumerinu (IZ, 5 mm at 200 μg/disk) [63]. By comparison to known compound helicascolide A, the C-3 keto group of 71 (the red moiety shown in the structure of 71) enhances the antifungal activity.

Figure 16

Structures of compound 66–71 (the red moiety enhances the antimicrobial activity).

Structures of compound 62–65 (the red moiety enhances the antimicron class="Chemical">bial activity).

Structures of compound 66–71 (the red moiety enhances the antimicron class="Chemical">bial activity).

The structures of compound 72–76 were shown in Figure 17. Communol A (72) was isolated from P. commune 518 and showed weak antin class="Chemical">bacterial activity against E. coli and E. aerogenes (MIC, 4.1 μM and 16.4 μM, respectively) [64]. Aspergillumarin A (73) and B (74) were isolated from Aspergillus sp. and exhibited weak activities against S. aureus and B. subtilis at 50 µg/mL [65]. Bromomethylchlamydosporols A (75) and B (76) were isolated from Fusarium tricinctum. The addition of CaBr2 to the fermentation media resulted in the production of two halogenated chlamydosporol analogs, 75 and 76. Compounds 75 and 76 showed the same activity against three strains of S. aureus (MIC, 15.6 µg/mL) [66].

Figure 17

Structures of compound 72–76.

The structures of compound 77–84 were shown in Figure 18. Three tricyclic lactones and one tetracyclic n class="Chemical">lactone with antimicrobial activities were isolated from Coniothyrium cereale (Z)-coniosclerodinol (77), conioscleroderolide (78), (15S,17S)-(−)-sclerodinol (79) and coniolactone(80), repectively. Moreover, coniosclerodione (81), with activity against S. aureus (MIC, 65.7 μM) as well as Micrococcus luteus and Mycobacterium phlei (IZ, 10 and 12 mm at 20 μg/disk, respectively),was isolated from the same fungal strain [67]. By comparison with its analogs, the activity against M. phlei. (IZ, 16 mm at 20 μg/disk) of 77 is related to its C-18 hydrogens and C-19 hydroxyl. Moreover, antibacterial activity seems to correlate with the presence of a diketo-lactone ring as found in compound 78. The C-19 hydroxyl of 79 is also important for its activity against M. phlei (IZ, 20 mm at 20 μg/disk). Compound 82 was isolated from E. rubrum G2 and elucidated as 9-dehydroxyeurotinone with weak antibacterial activity against E. coli (IZ, 7 mm at 100 mg/disk) [68]. Acremostrictin (83) is another tricyclic lactone that was isolated from A. strictum,and it exhibited weak activity against M. luteus, Salmonella typhimurium and Proteus vulgaris (MIC, 50, 50 and 12.5 μg/mL, respectively) [69]. Flavipesin A (84) was isolated from A. flavipes AIL8 and demonstrated antibacterial activity against S. aureus (MIC, 8.0 μg/mL) and B. subtillis (0.25 μg/mL). Flavipesin A (84) also demonstrated activity against biofilm formation and could penetrate the mature biofilm matrix to kill the cell. Even penicillin cannot penetrate the polysaccharide barriers of a mature biofilm [70].

Figure 18

Structures of compound 77–84 (the red moiety enhances the antimicrobial activity).

Structures of compound 77–84 (the red moiety enhances the antimicron class="Chemical">bial activity).

The structures of compound 85–89 were shown in Figure 19. Austalide R (85), M (86) and N (87) were isolated from n class="Species">Aspergillus sp. and exhibited antibacterial activity against Halomonas aquamarina, Polaribacter irgensii, Pseudoalteromonas elyakovii, Roseobacter litoralis, Shewanella putrefaciens, V. harveyi, V. natriegens, V. proteolyticus and V. carchariae (MIC, 0.01–0.1 μg/mL for 85; 0.001–0.01 μg/mL for 86 and 0.01 μg/mL for 87). The R1 substituents at C-17 and R2 at C-22 (shown in the structures of 85 and 86) significantly enhance their antibacterial activities [20,71]. Talaromycesone A (88) and B (89) were isolated from Talaromyces sp. LF458 and exhibited potent antibacterial activities against human pathogenic S. epidermidis (IC50, 3.70 and 17.36 μM, respectively) and S. aureus MRSA (IC50, 5.48 and 19.50 μM, respectively) [72].

Figure 19

Structures of compound 85–89 (the red moiety enhances the antimicrobial activity).

Structures of compound 85–89 (the red moiety enhances the antimicron class="Chemical">bial activity).

Calcarides A–C (90–92) and E (93) (Figure 20) were isolated from n class="Species">Calcarisporium sp. KF525 and showed antibacterial activity against S. epidermidis and X. campestris (MIC, 68.8 and 5.5 μg/mL for 90; 53.2 and 22.6 μg/mL for 91; 29.6 and 61.4 μg/mL for 92; and 104.3 and more than 150 μg/mL for 93, respectively) [73]. In comparison to calcaride D that contains a hydroxyl, calcaride E (93) exhibited stronger activity with its hydrogen moiety. Three compounds, 6-hydroxymellein, β-hydroxybutyric acid and 6-methoxymellein, were proposed as the precursors of calcaride.

Figure 20

Structures of compound 90–93 (the red moiety enhances the antimicrobial activity).

Structures of compound 90–93 (the red moiety enhances the antimicron class="Chemical">bial activity).

Aflatoxin B2b (94) (Figure 21) was isolated from A. n class="Chemical">flavus 092008 and exhibited moderate antimicrobial activity against E. coli, B. subtilis and E. aerogenes (MIC, 22.5, 1.7 and 1.1 µM, respectively) [74]. Compound 94 was elucidated to be the 4-methoxy-4-oxobutanoyl substitution for the acetyl group of 8-acetyloxyaflatoxin B1. By comparison to 8-acetyloxyaflatoxin B1, the 4-methoxy-4-oxobutanoyl moiety partly contributes to the antibacterial activity of 94. Moreover, based on aflatoxins B1 and aflatoxins B1, the acetyloxy group of 8-acetyloxyaflatoxin B1 is not related to the antibacterial activity. Isochromophilone XI (95) (Figure 21) was isolated from Bartalinia robillardoides LF550 and showed antibacterial and antifungal activities against B. subtilis, S. lentus and Trichophyton rubrum (MIC, 55.6, 78.4 and 41.5 μM, respectively). The oxygen in the pyran ring of 95 is important for its antibacterial and antifungal activities, as determined by comparison to inactive analogs of 95 [75,76].

Figure 21

Structures of compound 94–95 (the red moiety enhances the antimicrobial activity).

Structures of compound 94–95 (the red moiety enhances the antimicron class="Chemical">bial activity).

Comazaphilones A–F (96–101) (Figure 22) were isolated from n class="Species">P. commune QSD-17. Comazaphilones C–E (98–100) displayed potent antibacterial activities against S. aureus MRSA, P. fluorescens and B.subtilis (MIC, 16, 64 and 32 μg/mL for 98; 32, 16 and more than 256 μg/mL for 99; and more than 256 μg/mL, 32 and 16 μg/mL for 100, respectively). The SAR results indicated that the double bond at C-10 of 98–100, as well as the location of the orsellinic acid unit at C-6 of 99 and 100 are important for their activity [77].

Figure 22

Structures of compound 96–101.

The structures of compound 102–105 were shown in Figure 23. Isomonodictyphenone (102) was isolated n class="Species">Penicillium sp. MA-37 and showed potent antibacterial activity against Aeromonas hydrophilia (MIC, of 8 μg/mL) [78,79]. Communol F (103) and communol G (104) were isolated from P. commune 518 and showed weak antimicrobial activities against E. coli and E. aerogenes (MIC, 6.4 and 25.8 μM for 103; and 23.8 and 23.8 μM for 104, respectively) The CHO moiety of 105 and the CH2OH of 104 at C-3 are important for their activities, as determined by comparison to their inactive analogs [64]. Compound 105 was isolated from the co-culture of fungal strains E33 and K38 and exhibited antifungal activity against F. graminearum, Gloeosporium musae, Rhizoctonia solani and Phytophthora sojae (IZ, 12.1, 11.6, 10.2 and 8.5 mm at 0.25 mM, respectively) [49].

Figure 23

Structures of compound 102–105 (the red moiety enhances the antimicrobial activity).

Structures of compound 102–105 (the red moiety enhances the antimicron class="Chemical">bial activity).

5.4. Others

The structures of compound 106–111 were shown in Figure 24. Penicitrinols J (106) and K (107) were isolated from n class="Species">Penicillium sp. ML226 and showed antimicrobial activity against S. aureus CMCC26003 (IZ, 4 and 3 mm at 20 μg/disk, respectively) [80]. Pestalachloride D (108) was isolated from Pestalotiopsis sp. (ZJ-2009-7-6) and showed antibacterial activity against E. coli, V. anguillarum and V. parahaemolyticus (MIC, 5.0, 10.0 and 20.0 μM, respectively) [81]. Cordyols E (109) was isolated from Aspergillus sp. XS-20090066 and showed antibacterial activity against all test bacteria S. epidermidis, S. aureus, V. anguillarum, V. parahemolyticus and P. putida (MIC, 25.6–51.2 μM). The methoxyl group of 109 at C-3 is related to its activity, as determined by comparison to the hydroxyl of diorcinol (a known antimicrobial compound) at C-3 [82]. Microsphaerol (110) was isolated from Microsphaeropsis sp. No. 7820 and showed antibacterial activity against E. coli, B. megaterium and Microbotryum violaceum (IZ, 8, 9 and 9 mm at 50 μg/disk, respectively) [58]. Compound 111 was isolated from Penicillium sp. MA-37 and elucidated as 7-O-acetylsecopeni-cillide C (111), which was active against M. luteus and E. coli (MIC, 64 and 16 μg/mL, respectively) [79]. The acetoxyl at C-7 of 111 is important to its antibacterial activity, which was determined by comparison of the hydroxyl at C-7 in the active secopenicillide C that is substituted by an acetoxyl group at C-7 in 111.

Figure 24

Structures of compound 106–111 (the red moiety enhances the antimicrobial activity).

The structures of compound 112–116 were shown in Figure 25. Compound 112 was isolated from Spicaria elegans KLA-03 and showed antin class="Chemical">bacterial and antifungal activities against E. aerogenes, E. coli., P. aeruginosa, S. aureus and C. albicans (MIC, 0.15, 0.04, 0.77, 1.53 and 0.38 μM, respectively) [83]. Felinone B (113) was isolated from B. felina EN-135 and it showed inhibitory activity against P. aeruginosa (MIC, 32 μg/mL) [84]. Isoacremine D (114), an isomer of 113, was isolated from Myceliophthora lutea and exhibited antibacterial activity against S. aureus (MIC, 200 μg/mL) [85]. Compound 115 was isolated from Aspergillus sp. ZJ-2008004 and exhibited two Gram-positive bacteria, S. albus and B. subtilis (MIC, 5 and 2.5 μM, respectively) [41]. New fatty acid glycoside 116 was isolated from Scyphiphora hydrophyllacea A1 and showed inhibitory effects on S. aureus and MRSA (IZ, 3.8 and 4.7 at 500 μg/disk, respectively) [86].

Figure 25

Structures of compound 112–116.

Structures of compound 106–111 (the red moiety enhances the antimicron class="Chemical">bial activity).

6. Known Antibacterial and Antifungal Compounds from Marine Fungi

As shown in Table 1, there are 169 known compounds 117–285 from marine fungi showing antin class="Chemical">bacterial or antifungal activities (structures are shown in supplement materials Figure S2). Compounds 142, 187, 230, 255, 263, 271 and 272 were isolated for the first time from natural sources [31,87,88,89]. Compounds 128, 168, 169, 187, 203, 222, 234, 235, 241 and 267 were evaluated for their antimicrobial activities for the first time [15,19,90,91,92,93]. The data shown in Table 1 would be useful for the utilization of these antibacterial and antifungal compounds from marine fungi as lead compounds for future medicine.

Table 1

Known compounds 117–285 with antibacterial or antifungal activities isolated from marine fungi.

Compound name	Activity	Reference	Compound name	Activity	Reference
(−)-scleroderolide (117)	B+, Y	[67]	(−)-sclerodione (118)	B+, Y	[67]
(−)-sclerotiorin (119)	Y, F	[94]	(−)-stephacidin A (120)	B+	[82]
(±)-pestalachloride C (121)	B−	[81]	(5α,6α)-ophiobolin H (122)	B−	[45]
15G256β (123)	B	[73]	15G256α (124)	B	[73]
15G256π (125)	B+	[73]	1-methyl emodin (126)	B	[54]
2,5-furandimethanol (127)	B+	[36]	3-HPA (128)	B+	[90]
4-deoxybostrycin (129)	B	[57]	4-hydroxybenzaldehyde (130)	B−	[95]
6,8-di-O-methylaverufin (131)	B	[96]	6-epi-ophiobolin G (132)	B+	[97]
6-epi-ophiobolin K (133)	B+	[97]	6-O-methylaverufin (134)	B	[96]
7-nor-ergosterolide (135)	Y, B	[33]	8-acetyloxyaflatoxin B1 (136)	B−	[74]
acetylgliotoxin (137)	B+	[87]	adenosine (138)	B−	[98]
aflatoxins B1 (149)	B−	[74]	aflatoxins B2 (140)	B−	[74]
AGI-B4 (141)	B	[42]	alternariol 2,4-dimethyl ether (142)	B−	[31]
anicequol (143)	F	[39]	AS-186c (144)	B+	[72]
aspergillazine A (145)	B, Y	[83]	aspergillin PZ (146)	B+	[34]
aspergillusene A (147)	B−	[99]	aspergillusidone C (148)	B+	[100]
aspergillusone B (159)	B	[42]	asperphenamate (150)	B+	[34]
aspochalasin E (151)	B, Y	[83]	aspochalasin D (152)	B	[34]
aspochalasin I (153)	B+	[34]	aspulvinone E (154)	B, Y	[83]
averantin (155)	B+	[101]	averufin (156)	B+	[101]
bostrycin (157)	B	[56]	brefeldin A (158)	Y	[102]
brevianamide M (159)	B	[96]	butyrolactone I (160)	B+	[88]
chlamydosporol (161)	B+	[66]	cholesteryl linoleate (162)	B+	[36]
chrysazin (163)	Y	[103]	cis-cyclo(Leu-Tyr) (164)	B+	[104]
citrinin (165)	B	[105]	CJ-17665 (166)	Y	[32]
cladosporin (167)	B+	[106]	conidiogenol (168)	B	[91]
conidiogenones B (169)	B, Y	[91]	coniothranthraquinone 1 (170)	B+	[53]
cordyol C (171)	B	[82]	cpicpoformin (172)	B+	[106]
cyclo(d)-Pro-(d)-Val (173)	B−	[31]	cyclosporine A (174)	Y, F	[107]
cytochalasin Z17 (175)	B−	[20]	cytosporone B (176)	B+	[108]
cytosporone E (177)	B+	[108]	deacetylsclerotiorin (178)	B+, Y	[75,76]
dechlorogriseofulvin (179)	Y	[48]	dicerandrol C (180)	B+	[109]
dihydroisoflavipucine (181)	B	[20,71]	diorcinol (182)	B+	[99,110]
djalonensone (183)	B−	[111]	echinulin (184)	B+	[19]
epolones B (185)	Y	[102]	ergone (186)	B+,Y	[112]
eurorubrin (187)	B−	[92]	fonsecin (188)	F	[113]
fumitremorgin B (189)	B−	[114]	furandimethanol (190)	B+	[98]
fusaric acid (191)	B+	[115]	fusarielin A (192)	B+	[66]
gliotoxin (193)	B	[87]	globosuxanthone A (194)	Y	[103]
glyantrypine (195)	B−	[114]	griseofulvin (196)	Y	[48]
griseophenone C (197)	B	[48]	guignardones B (198)	B+	[44]
helicusin A (199)	Y	[76]	hydroxysydonic acid (200)	B	[42]
stachybocin A (201)	B+	[23]	ilicicolin B (202)	B+	[23]
isaridin E (203)	B−	[84]	isochaetochromin B2 (204)	B+	[116]
isorhodoptilometrin (205)	B+	[53]	lapatins B (206)	B−	[114]
malformins A1 (207)	B+	[117]	malformins C (208)	B+	[117]
meleagrin (209)	B+, Y	[95]	methylaverantin (210)	B+	[101]
N-acetyldopamine (211)	F	[95]	neoaspergillic acid (212)	B	[118]
nidulin (213)	B+	[100]	nidurufin (214)	B+	[101]
nigrosporin B (215)	B	[119]	nornidulin (216)	B+	[100]
notoamide B (217)	Y	[32]	notoamide R (218)	Y	[32]
ophiobolin K (219)	B+	[97]	oxasetin (220)	B−	[120]
patulin (221)	B+	[106]	penicillixanthone A (222)	B	[93]
pestalone (223)	B+, F	[121]	phomaligol A (224)	B+	[35]
phomazine B (225)	F	[22]	phyllostine (226)	B+	[106]
pycnidione (227)	Y	[102]	pyridoxatin (228)	B+, Y	[24]
pyrophen (229)	Y	[113]	reduced gliotoxin (230)	B	[87]
rubralide C (231)	B−	[31]	rubrofusarin B (232)	Y	[113]
sclerotiamide (233)	Y	[32]	secalonic acid B (234)	B	[93]
secalonic acid D (235)	B	[93]	siderin (236)	B	[54]
sporogen AO-1 (237)	Y	[122]	stachybocin B (238)	B+	[23]
stephacidin A (239)	Y	[32]	stigmasterol (240)	B+	[36]
tardioxopiperazine A (241)	B	[19]	tetrahydrobostrycin (242)	B	[48]
trichodermamide B (243)	B, Y	[83]	trichodermamides A (244)	B, Y	[83]
tyrosol (245)	B+	[98]	ustilaginoidin D (246)	B+	[116]
verruculogen (247)	B−	[114]	waikialides A (248)	Y	[32]
waikialides B (249)	Y	[32]	xanthocillin X (250)	B, F	[95]
Compound name				Activity	Reference
ω-hydroxyemodin (251)				B+	[53]
(3β,5α,8α,22E)-5,8-epidioxyergosta-6,9,22-trien-3-ol (252)				B+	[112]
(−)-7,8-dihydro-3,6-dihydroxy-1,7,7,8-tetramethyl-5H-furo-[2¢,3¢:5,6]naphtho[1,8-bc]furan-5-one (8) (253)				B+	[67]
(Z)-5-(hydroxymenthyl)-2-(60)-methylhept-2′-en-2′-yl)-phenol (254)				B−	[41,99]
1,2,3,4-tetrahydro-2-methyl-3-methylene-1,4-dioxopyrazino[1,2-α]indole (255)				B+	[87]
1,3,8-trihydroxy-6-methylanthracene-9,10-dione (256)				B	[53,54]
2-(hydroxymethyl)benzene-1,4-diol (257)				B+	[89]
2-carboxymethyl-3-hexylmaleic acid anhydride (258)				F	[61]
2-methylbenzene-1,4-diol (259)				B+	[89]
3-(3-hydroxy-5-methylphenoxy)-5-methylphenol (260)				B	[82]
3,1′-didehydro-3[2″(3‴,3‴-dimethyl-prop-2-enyl)-3″-indolylmethylene]-6-methyl pipera-zine-2,5-dione (261)				B−	[123]
3,6,8-trihydroxy-1-methylxanthone (262)				B	[48]
3,9-dimethyldibenzo[b,d]furan-1,7-diol (263)				B+	[88]
3b-hydroxyergosta-8,24(28)-dien-7-one (264)				B+	[33]
3-hydroxy-4-((S)-2-hydroxy-6-methylheptan-2-yl)benzoic acid (265)				B−	[99]
3-hydroxy-5-methyl-5,6-dihydro-7H-cyclopenta[b]pyridin-7-one (266)				B+	[124]
3-O-(a-d-ribofuranosyl)questin (267)				B−	[92]
3β,5α-dihydroxy-(22E,24R)-ergosta-7,22-dien-6β-yl oleate (268)				B+	[112]
4-deoxytetrahydrobostrycin (269)				B−	[48]
4-methoxycarbonyldiorcinol (270)				B	[82]
4-O-methyltoluhydroquinone toluhydroquinone (271)				B+	[89]
5-bromotoluhydroquinone toluhydroquinone (272)				B+	[89]
6,8-di-O-methylnidurufin (273)				B	[55]
6,8-di-O-methylversiconol (274)				B−	[55]
6-[2-hydroxy-6-(hydroxymethyl)-4-methylphenoxy]-2-methoxy-3-(1-methoxy-3-methylbutyl)benzoic acid (275)				B	[78,79]
9α-hydroxydihydrodesoxybostrycin (276)				B	[56]
8-O-4-dehydrodiferulic acid (277)				B−	[20,71]
9α-hydroxyhalorosellinia A (278)				B	[56]
cyclo-trans-4-OH-(d)-Pro-(d)-Phe (279)				B−	[31]
methyl 3,4,5-trimethoxy-2-(2-(nicotinamido) benzamido) benzoate (280)				B+	[29]
N-methylphenyldehydroalanyl-l-prolin-anhydrid (281)				B−	[31]
O-methyldihydrobotrydial (282)				B+	[21]
stigmasta-7,22-diene-3β,5α,6α-triol (283)				B+	[112]
tetranorditerpenoid derivative (284)				Y	[125]
tricycloalternarene 3α (285)				B−	[111]

Activities: B+ means against Gram-positive bacteria; B− means against Gram-negative bacteria; B means against both Gram-positive and Gram-negative bacteria; Y means against yeast; and F means against filamentous fungi.

Activities: B+ means against Gram-positive n class="Chemical">bacteria; B− means against Gram-negative bacteria; B means against both Gram-positive and Gram-negative bacteria; Y means against yeast; and F means against filamentous fungi.

7. Conclusions

The resource of marine fungal species is abundant and the cultivan class="Chemical">ble marine fungal strains are easily isolated and cultured. However, it is difficult to discover the marine fungi with special metabolites. To facilitate the discovery process, there are several methods to screen the marine fungi before further purification of their antimicrobial compounds. The taxonomic information, the screening of antimicrobial activity for the extracts from marine fungi, the analysis of the genes related to secondary metabolism and the comparison of the chemical profiles with the literature can contribute to the screening of special fungal strains. ITS sequence analysis cannot only afford the taxonomic information, but also facilitates investigation and acquisition of the closest fungal strain by their accession numbers. Therefore, obtaining the ITS sequence is recommended for every study. It can become the bridge between biology and chemistry. Another molecular biological method, analysis of the genes related to secondary metabolism, could be used for screening the marine fungi producing new antibacterial and antifungal compounds. Furthermore, there is previous research investigating the diversity of type I polyketide synthase (PKS I) genes from many marine fungi to find potential fungi producing new antibacterial and antifungal compounds [112].

The fermentation conditions of the potn class="Chemical">ential fungal strain significantly affect the secondary metabolism of marine fungi. Some of the new antimicrobial compounds from marine fungi are only produced under high salinity [33,48,66]. The fungal strains that new antimicrobial compounds have been isolated from are recommended for investigation of their metabolic changes under different fermentation processes (especially under high salinity). The potential of these fungi have been proven, thus it is possible that more new antimicrobial compounds will be discovered under different fermentation conditions.

The Aspergillus gn class="Chemical">enus is one of the dominant marine fungal genera and the marine fungal strains from Aspergillus produced more new antibacterial and antifungal compounds than any other genus. Furthermore, EtOAc is the most common solvent for the extraction of marine fungal cultures, which can also extract abundant compounds from mycelia or liquid culture, especially compounds with low or medium polarity. It is one of the reasons that water-soluble compounds (polar compounds) with antibacterial or antifungal activities from marine fungi are fewer than those from actinomyces and bacteria. For the antibacterial or antifungal tests of the compounds from marine fungi, S. aureus, B. subtilis, E. coli and C. albicans were recommended as the test microorganisms, and commercial antibiotics were used as positive controls, which is a convenient comparison for the compounds from different marine fungi. Importantly, the stereochemical configurations of the marine fungal compounds affect their antibacterial or antifungal activities. Thus, the stereochemical configurations of the pure compounds should be elucidated and evaluated for their activity mechanisms. In addition, typically too few compounds with similar structures for a structure-activity relationship can be purified from marine fungi; therefore, the total synthesis or a group derivation of compounds from marine fungi may help solve this problem. The bacterial or fungal mutant with a resistant gene to the antibacterial or antifungal compounds, morphological microscopic observation of the test microorganisms and RNA sequencing are recommended to contribute to understanding the mechanism of antibacterial or antifungal activities. This information will be beneficial for further utilization and development of antibacterial and antifungal compounds from marine fungi.

Taken together, these data indicate that marine fungi are a good new antin class="Chemical">bacterial and antifungal compound source. Many novel antibacterial and antifungal compounds that are only produced by these marine fungi have been discovered. There will certainly be more antibacterial and antifungal compounds from marine fungi as lead compounds for medicines and pesticides in the future.