Polyhydroxybutyrate production in halophilic marine bacteria Vibrio proteolyticus isolated from the Korean peninsula

Polyhydroxybutyrates (PHB) are biodegradable polymers that are produced by various microbes, including Ralstonia, Pseudomonas, and Bacillus species. In this study, a Vibrio proteolyticus strain, which produces a high level of polyhydroxyalkanoate (PHA), was isolated from the Korean marine environment. To determine optimal growth and production conditions, environments with different salinity, carbon sources, and nitrogen sources were evaluated. We found that the use of a medium containing 2% (w/v) fructose, 0.3% (w/v) yeast extract, and 5% (w/v) sodium chloride (NaCl) in M9 minimal medium resulted in high PHA content (54.7%) and biomass (4.94 g/L) over 48 h. Addition of propionate resulted in the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-co-HV)) copolymer as propionate acts as a precursor for the HV unit. In these conditions, the bacteria produced poly(3-hydroxybutyrate-co-3-hydroxyvalerate) containing a 15.8% 3HV fraction with 0.3% propionate added as the substrate. To examine the possibility of using unsterilized media with high NaCl content for PHB production, V. proteolyticus was cultured in sterilized and unsterilized conditions. Our results indicated a higher growth, leading to a dominant population in unsterilized conditions and higher PHB production. This study showed the conditions for halophilic PHA producers to be later implemented at a larger scale.