K Chakraborty1,2, V K Kizhakkekalam1,2, M Joy1,2. 1. Marine Bioprospecting Section of Marine Biotechnology Division, Central Marine Fisheries Research Institute, Ernakulam North, P.B. No. 1603, Cochin, India. 2. Faculty of Marine Sciences, Cochin University of Science and Technology, Kerala State, Lakeside Campus, Cochin, India.
Abstract
AIMS: Biotechnological and chemical characterization of previously undescribed homologous siderophore-type macrocyclic polyketides from heterotrophic Shewanella algae Microbial Type Culture Collection (MTCC) 12715 affiliated with Rhodophycean macroalga Hypnea valentiae of marine origin, with significant anti-infective potential against drug-resistant pathogens. METHODS AND RESULTS: The heterotrophic bacterial strain in symbiotic association with intertidal macroalga H. valentiae was isolated to homogeneity in a culture-dependent method and screened for bioactivities by spot-over-lawn assay. The bacterial organic extract was purified and characterized by extensive chromatographic and spectroscopic methods, respectively, and was assessed for antibacterial activities with disc diffusion and microtube dilution methods. The macrocyclic polyketide compounds exhibited wide-spectrum of anti-infective potential against clinically significant vancomycin-resistant Enterococcus faecalis (VREfs), methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and Klebsiella pneumonia with minimum inhibitory concentration of about 1-3 µg ml-1 , insomuch as the antibiotics chloramphenicol and ampicillin were active at ≥6·25 µg ml-1 . The studied compounds unveiled Fe3+ chelating activity, which designated that their prospective anti-infective activities against the pathogens could be due to their siderophore mechanism of action. In support of that, the bacterium exhibited siderophore production on bioassay involving the cast upon culture agar plate, and the presence of siderophore biosynthetic gene (≈1000 bp) (MF 981936) further corroborated the inference. In silico molecular modelling with penicillin-binding protein (PBP2a) coded by mecA genes of MRSA (docking score -11·68 to -12·69 kcal mol-1 ) verified their in vitro antibacterial activities. Putative biosynthetic pathway of macrocyclic polyketides through stepwise decarboxylative condensation initiated by malonate-acyl carrier protein further validated their structural and molecular attributes. CONCLUSIONS: The studied siderophore-type macrocyclic polyketides from S. algae MTCC 12715 with significant anti-infective potential could be considered as promising candidates for pharmaceutical and biotechnological applications, especially against emerging multidrug-resistant pathogens. SIGNIFICANCE AND IMPACT OF THE STUDY: This study exhibited the heterotrophic bacteria in association with intertidal macroalga as propitious biological resources to biosynthesize novel antibacterial agents.
AIMS: Biotechnological and chemical characterization of previously undescribed homologous siderophore-type macrocyclicpolyketides from heterotrophic Shewanella algae Microbial Type Culture Collection (MTCC) 12715 affiliated with Rhodophycean macroalga Hypnea valentiae of marine origin, with significant anti-infective potential against drug-resistant pathogens. METHODS AND RESULTS: The heterotrophic bacterial strain in symbiotic association with intertidal macroalga H. valentiae was isolated to homogeneity in a culture-dependent method and screened for bioactivities by spot-over-lawn assay. The bacterial organic extract was purified and characterized by extensive chromatographic and spectroscopic methods, respectively, and was assessed for antibacterial activities with disc diffusion and microtube dilution methods. The macrocyclicpolyketide compounds exhibited wide-spectrum of anti-infective potential against clinically significant vancomycin-resistant Enterococcus faecalis (VREfs), methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and Klebsiella pneumonia with minimum inhibitory concentration of about 1-3 µg ml-1 , insomuch as the antibiotics chloramphenicol and ampicillin were active at ≥6·25 µg ml-1 . The studied compounds unveiled Fe3+ chelating activity, which designated that their prospective anti-infective activities against the pathogens could be due to their siderophore mechanism of action. In support of that, the bacterium exhibited siderophore production on bioassay involving the cast upon culture agar plate, and the presence of siderophore biosynthetic gene (≈1000 bp) (MF 981936) further corroborated the inference. In silico molecular modelling with penicillin-binding protein (PBP2a) coded by mecA genes of MRSA (docking score -11·68 to -12·69 kcal mol-1 ) verified their in vitro antibacterial activities. Putative biosynthetic pathway of macrocyclicpolyketides through stepwise decarboxylative condensation initiated by malonate-acyl carrier protein further validated their structural and molecular attributes. CONCLUSIONS: The studied siderophore-type macrocyclicpolyketides from S. algae MTCC 12715 with significant anti-infective potential could be considered as promising candidates for pharmaceutical and biotechnological applications, especially against emerging multidrug-resistant pathogens. SIGNIFICANCE AND IMPACT OF THE STUDY: This study exhibited the heterotrophic bacteria in association with intertidal macroalga as propitious biological resources to biosynthesize novel antibacterial agents.