Effects of nutrient and oxygen limitation, salinity and type of salt on the accumulation of poly(3-hydroxybutyrate) in Bacillus megaterium uyuni S29 with sucrose as a carbon source.

Due to high manufacturing costs, industrial production and application of bio-based polyhydroxyalkanoates (PHA) as bioplastics remain below the expected potential. Improving yields and productivities during biotechnological production will contribute to eliminating existing shortcomings and should therefore be a priority in process development with new strains and substrates. The present study investigates key parameters such as different nutrient and oxygen limitation strategies and the salinity and type of salt to determine their impact on growth and poly(3-hydroxybutyrate) (P(3HB)) formation behaviour of Bacillus megaterium. The oxygen-limiting conditions applied resulted in a longer process duration and were found to be least effective with regard to P(3HB) content in the biomass. A higher P(3HB) content of 0.42 g g was achieved when nitrogen was limited compared to 0.34 g g under phosphate-limiting conditions; however, sucrose utilization was better when phosphate was limited. Replacing NaCl by KCl and evaluating different concentrations ranging from 0.08 to 1.7 mol L in the process medium showed that B. megaterium has a higher tolerance to KCl as the biomass and P(3HB) formation was increased to 0.48 g g compared to 0.36 g g. The combination of applying KCl instead of NaCl together with phosphorous limitation significantly increased P(3HB) productivity to 0.25 g L h compared to 0.09 g L h. It can be concluded that the effective utilization of sucrose as a carbon source requires a combination of high nitrogen and low phosphorous concentration and a salt content of 0.6 g L KCl for P(3HB) production with B. megaterium uyuni S29.