Enhanced production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer by endophytic Bacillus cereus RCL 02 utilizing sugarcane molasses as sole source of carbon: a statistical optimization approach

Polymers of biological origin have become a topic of interest due to growing concerns about the environmental impact of the disposal of plastics. In recent years, the production of ecobenign microbial polymer polyhydroxyalkanoates (PHAs) using inexpensive and renewable resources has gained significant interest as these compounds are highly biodegradable, biocompatible, and sustainable. This study used leaf endophytic isolate Bacillus cereus RCL 02, obtained from the oil-yielding plant Ricinus communis L., to achieve statistical optimization of culture variables for the enhanced production of PHAs utilizing sugarcane molasses as the sole carbon source. A three-level and four-factor Box–Behnken design of response surface methodology was implemented to optimize the process variables, namely molasses (carbon substrate), ammonium sulfate (nitrogen source), initial pH, and incubation period, for improved biomass formation and PHA production. The highest growth (14.8 g/l) and PHA production (85.2%, dry cell weight) by the isolate were observed with 47 g/l molasses, 3 g/l ammonium sulfate, an initial pH of 6.7, and 62 h of incubation. Statistical optimization of the process allowed achieving a 1.6-fold increase in the PHA yield (7.8–12.6 g/l) compared with the conventional single-factor system of analysis. The biopolymer thus produced was confirmed as a copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate [P(3HB-co-3HV)] using 1H nuclear magnetic resonance spectroscopic analysis and was found to contain 7.8 mol% 3-hydroxyvalerate. These findings clearly indicate the efficacy of the B. cereus RCL 02 isolate in the biotransformation of raw sugarcane molasses to P(3HV-co-3HV), without the need for supplementation with high-cost precursors.