Process optimisation and genomic analysis of poly(3-hydroxybutyrate) production by Mycolicibacterium smegmatis using sugarcane bagasse

Abstract

This study investigates the optimisation of poly(3-hydroxybutyrate) (PHB) production by Mycolicibacterium smegmatis using sugarcane bagasse (SCB) hydrolysate as a low-cost, renewable carbon source. Key fermentation parameters including temperature, pH, agitation, inoculum size and nitrogen supplementation were optimised to enhance biomass growth and PHB accumulation. Under optimised conditions (37 °C, pH 7, 100 rpm, 3% inoculum), M. smegmatis achieved a maximum PHB content of 64% of DCW from SCB hydrolysate, corresponding to a PHB titre of ~ 1.0 g L−1 and a volumetric productivity of 0.014 g L−1 h−1 after 72 h of cultivation, with yeast extract identified as the most effective nitrogen source. Thin-layer chromatography (TLC) analysis demonstrated that M. smegmatis could not only co-utilise glucose and xylose simultaneously but preferentially consumed xylose, which is a major advantage when processing lignocellulosic biomasses, where xylose is abundant and typically underutilised by many microorganisms. Whole-genome sequencing with Oxford Nanopore Technologies (ONT) confirmed the presence of PHB production genes (phbA, phbB, phbC) and a xylose-utilisation pathway, supporting its metabolic capability. These findings establish M. smegmatis as a promising candidate for converting agricultural waste into biodegradable bioplastics, contributing to circular bioeconomy strategies.