Kinetics and synthesis of poly(3-hydroxybutyrate) by a putative-mutant of Bacillus licheniformis

Abstract

The present study deals with the kinetics of improved poly(3-hydroxybutyrate) (PHB) production by an L-cysteine HCl-depressed mutant of Bacillus licheniformis. Production of biodegradable polymers is to eliminate use of materials derived from petrochemicals and also because of their environmental impact. For the current study, mutant strain (NA-21) & wild-type (IIB-isl19) were used for PHB production. Submerged culture with two-stage fermentation technique was used for PHB production. Results indicated that PHB production was improved with 300 mM of –HNO2. The superior mutant strain (NA-21) resulted in 2-fold more PHB as compared to the wild-type (IIB-isl9). It was selected, and resistance against L-cysteine HCl was developed. At 4 ppm concentration of L-cysteine HCl, PHB production by mutant strain (NA-cys4) was higher than its wild counterpart by 5.7-fold. Kinetic study of parameters including specific growth rate (µ h− 1), growth (Yx/s,Ys/x), product yield coefficients (Yp/s,Yp/x), volumetric rate constants (Qp, Qs, Qx) and specific rate constants (qp, qs, qx), were also accomplished. Moreover, Yp/x, Qp and qp = µ × Yp/x were found to be very significant as 1.254 ± 0.06 (g/g biomass), 0.134 ± 0.01 (g/l/h) and 0.168 ± 0.01 (g/g/h), respectively. The effect of fatty acids on PHB production highlighted the improvement in PHB production by 1.94-fold. The highest PHB production during the study was 16.35 ± 3.12 g/l which highlighted its significance (p ≤ 0.05) and impact on the overall process. The variation in PBH yield between wild-type and mutant B. licheniformis is possibly because of induced DNA interstrand thus making unstable thymidine-thymidine dymers. From the results, it was concluded that improved PHB production on industrial scale is fairly possible and it holds the potential to contribute significantly to plastic circularity in the future.