[Halomonas uses short-chain fatty acids to synthesize polyhydroxyalkanoates]

Halomonas can grow on diverse carbon sources. As it can be used for unsterile fermentation under high-salt conditions, it has been applied as a chassis for next-generation industrial biotechnology. Short-chain volatile fatty acids, including acetate, propionate, and butyrate, can be prepared from biomass and are expected to be novel carbon sources for microbial fermentation. Halomonas sp. TD01 and TD08 were subjected to shaking culture with 10-50 g/L butyrate, and they were found to effectively synthesize poly-3-hydroxybutyrate with butyrate as the carbon source. The highest yield of poly-3-hydroxybutyrate was achieved at butyrate concentration of 20 g/L (9.12 g/L and 7.37 g/L, respectively). Butyrate at the concentration > 20 g/L inhibited cell growth, and the yield of poly-3-hydroxybutyrate decreased to < 4 g/L when butyrate concentration was 50 g/L. Moreover, Halomonas sp. TD08 can accumulate the copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate by using propionate and butyrate as carbon sources. However, propionate was toxic to cells. To be specific, when 2 g/L propionate and 20 g/L butyrate were simultaneously provided, cell dry weight and polymer titer were 0.83 g/L and 0.15 g/L, respectively. The addition of glycerol significantly improved cell growth and boosted the copolymer titer to 3.95 g/L, with 3-hydroxyvalerate monomer content of 8.76 mol%. Short-chain volatile fatty acids would be promising carbon sources for the production of polyhydroxyalkanoates by Halomonas.