Isolation of Gram-positive Firmibacteria as major eicosapentaenoic acid producers from subtropical marine sediments.

In this study, a total of 172 putative omega-3 producers were isolated from 28 sediment samples from the Arabian Gulf employing a selective isolation procedure using marine agar containing 0·1% triphenyl tetrazolium chloride (TTC). Out of these 172 isolates, 19 isolates produced eicosapentaenoic acid (EPA) as confirmed by Gas Chromatography-Mass Spectrometry (GC-MS). The EPA content of the isolated bacterial strain varied from 1·76 to 6·52% of total fatty acids. Among the 19 isolates of EPA producers, while 17 isolates harboured both pfaA gene and Δ6 desaturase gene, only five isolates harboured Δ5 desaturase gene. Two of the EPA positive strains harbour none of the three genes tested. The 16s RNA identification of these isolates revealed that except one, all the EPA producers were Gram-positive marine bacteria belonging to the phylum Firmicutes, family Bacillacea, genera Bacillus and Oceanobacillus. Halomonas pacifica was the only Gram-negative Gamma-Proteobacteria detected to produce EPA from this region. SIGNIFICANCE AND IMPACT OF THE STUDY: Recently, marine bacteria are considered as a promising source of polyunsaturated fatty acid (PUFA) over marine fishes and microalgae. PUFA producers reported from polar and deep-sea sources were restricted to five well-known marine genera under two distinct domains of bacteria such as proteobacteria (Shewanella, Colwellia, and Moritella) and cytophaga group (Flexibacter, Psychroflexus). This study revealed that subtropical marine environment could also be the source of PUFA producing bacteria, and they predominantly belonged to the class of Firmibacteria. This finding opens up new avenue for research to study the inherent mechanism and physiology of such organisms from this unique environment.