Pentose-rich hydrolysate from acid pretreated rice straw as a carbon source for the production of poly-3-hydroxybutyrate

The aim of this work was to evaluate three different bacterial strains for their ability to accumulate poly-3-hydroxybutyrate (PHB) using pentose sugar rich hydrolysate generated from acid pretreated rice straw as the sole carbon source. Out of these, Bacillus firmus NII 0830 showed maximum PHB production. Acid pretreated black liquor contained sugars and sugar degradation products such as formic acid, acetic acid, furfural and hydroxymethyl furfural. The bacterium grew in the hydrolysate medium without any detoxification and it could accumulate 1.9 g/l biomass with 1.697 g/l PHB and the PHB content in the cell was 89%. This was the highest value ever reported from Bacillus species. The optimum conditions for the fermentation media were an inoculum concentration of 6.5%, 90 h of incubation and 0.75% of xylose concentration. The characterization of extracted polymer was carried out by FTIR, 1H and 13C NMR which showed characteristics similar to that of the standard PHB from Sigma.

► First report on biopolymer production from mild acid pretreated rice straw. ► B. firmus can grow in hydrolysate media without detoxification. ► Maximum PHB production was 1.697 g/l from 1.9 g/l biomass. ► Highest value (89% of biomass) reported from Bacillus species.