Development of a mini-repository of marine bacteria having the potential of Polyhydroxyalkanoates production

Polyhydroxyalkanoates (PHAs) are a well-studied substitute for conventional petroleum plastics of biological origin. The replacement of petroleum plastics with the PHAs has not been commercially successful, owing to the high cost involved in the production. A cost reduction method always involves searching for novel and highly productive strains for PHA production. In this study, focus was on the isolation of PHA producing marine bacteria from the North Eastern Arabian Sea, where periodic algal blooms are known to occur. Coastal samples were collected from the Goa Coast. We have isolated 347 PHA-producing isolates and made a mini repository of marine PHA producers, of which 16 isolates showed notable PHA accumulation based on cell dry weight. Molecular identification of these isolates using 16S rRNA gene sequencing revealed that PHA producing isolates belonged to the phyla Proteobacteria and Actinobacteria. Among the positive isolates, two were extreme halophiles, and others were halotolerant. The isolates Donghicola eburneus MCCB 271, Ruegeria mobilis MCCB 272, Labrenzia aggregata MCCB 274 and 275, Aeromicrobium sp. MCCB 341, Kocuria sp. MCCB 337, Alteromonas sp. MCCB 339 and 342, and Marinobacter hydrocarbonoclasticus MCCB 273 were identified as novel PHA producers when dextrose was used as a carbon source. One isolate MCCB 290, identified as Vibrio alginolyticus, showed the highest biomass yield of 4.69 ± 0.04 g L⁻¹ and PHA production of 73.67 % based on cell dry weight when grown in ZoBell's marine broth supplemented with 20 g L⁻¹ dextrose as a carbon source. The thermal characterization of the extracted polymers using Differential Scanning Calorimetry demonstrated a melting temperature (T_m) close to the commercial grade Polyhydroxybutyrate (PHB). Moreover, FTIR and GC analysis of the extracted polymer from the potent isolate MCCB 290 identified the polymer as PHB. The potential isolates have been maintained as the repository of PHA producing marine bacteria.