Biodiesel fuel is favored as a type of carbon neutral energy. To popularize its usage, by-product waste glycerol utilization is a critical problem. We tried to isolate waste glycerol utilizing bacteria, and obtained the alkalo- and halophile bacteria Halomonas sp. KM-1. This strain produced bioplastic poly(3-hydroxybutyrate) (PHB) in a simple medium and diluted waste glycerol as a sole carbon source.

To investigate the relationship between the production of poly(3-hydroxybutyrate) (PHB) and metabolic changes during different growth phases, a non-sterile batch fermentation process involving an alkalophilic and halophilic bacterium, Halomonas sp. KM-1, was used. Intracellular metabolites were analyzed using gas chromatography-mass spectrometry to characterize the metabolic profile. Significant changes relating to PHB production were observed in the TCA cycle, lipid-synthesis and amino acid biosynthetic pathways were found to shift dramatically between the exponential growth and stationary phases. During the stationary phase, 17 metabolites were upregulated and a cell dry mass of 17.8 g/L that included 44.8% PHB was observed at 24h in 5% glucose-supplemented cultures, whereas 11 metabolites were upregulated and a cell dry mass of 38.4 g/L that included 73.7% PHB was observed at 36 h in 10% glucose-supplemented cultures. This study provides pattern analysis of metabolite regulation during PHB accumulation, indicating that multicomponent and phase-specific mechanisms are involved.