Sustainable valorization of sugarcane molasses into polyhydroxybutyrate by Pseudomonas plecoglossicida MK-6 and optimization using response surface methodology.

Abstract

Polyhydroxybutyrate (PHB) is a biodegradable alternative to petrochemical plastics; however, its high production cost, largely attributed to the use of conventional carbon sources such as glucose, remains a major barrier. This study was designed to screen PHB-producing bacteria from dumping soil and evaluate the potential of sugarcane molasses, an agro-industrial waste, as a low-cost carbon source for PHB production. The PHB-positive isolate GSBB-5a2-2 was screened by using Sudan Black B and Nile Blue A staining techniques. The strain was identified as Pseudomonas plecoglossicida MK-6 based on partial 16 S rRNA gene sequencing (Gen Bank accession number. OQ236410). The optimal fermentation conditions were determined using a one-variable-at-a-time optimization approach. The maximum PHB production (7.3 g/L) was achieved with sugarcane molasses as the carbon source. A concentration of 5% sugarcane molasses as a carbon substrate and ammonium sulfate as a nitrogen source at a C: N ratio of 8:1 were found to be optimal for PHB production. The optimum physiological conditions were pH 7, 37 °C, 200 rpm, and an incubation time of 48 h. Response Surface Methodology (RSM) based on a Box-Behnken Design was employed to validate the experimental process. The extracted polymer was characterized by Fourier-transform infrared spectroscopy (FT-IR) confirming PHB production by Pseudomonas plecoglossicida MK-6 strain. Although PHB production by Pseudomonas plecoglossicida has been previously reported, the present study demonstrates the optimization of PHB synthesis using sugarcane molasses as a low-cost carbon substrate optimized through Response Surface Methodology, highlighting its potential for sustainable and cost-effective bioprocess development.

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