Isolation and Identification of Xylose-Utilising, Polyhydroxyalkanoate-Producing Bacteria from Sugarcane Bagasse: First Report of PHA Production by Mycolicibacterium Smegmatis

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters that are considered as alternatives to petroleum derived plastics. To reduce the production cost, many studies have focused on the use of sugarcane bagasse (SCB) as a cheap substrate for the biosynthesis of PHAs. Many microorganisms have been reported as PHA producers, but only a few can utilise xylose as a carbon source for their production. In this study, five xylose-utilising PHA producing bacteria (two mesophilic and three thermophilic) were isolated from decomposing SCB and assessed. Among the five isolates, Mycolicibacterium smegmatis, reported for the first time as a PHA producer, accumulated the highest amount of PHA using xylose (22% cell dry weight). M. smegmatis was then tested for its ability to utilise a mixture of simple sugars (2 glucose: 1 xylose) and alkaline pretreated SCB hydrolysate without any detoxification step. The results showed bacterial growth in both media; however, growth was lower in the media supplied with the hydrolysate (0.63 g L⁻¹) compared with a mixture of glucose and xylose (1.11 g L⁻¹), presumably due to the presence of inhibitors in the hydrolysate. PHA accumulation was similar in media supplied with hydrolysate or mixture, with 27% and 28% cell dry weight, respectively. The extracted biopolymer was studied by Fourier Transform Infrared (FTIR) spectroscopy, Gas Chromatography Mass Spectrometry (GC-MS) and Scanning Electron Microscopy (SEM) and identified as polyhydroxybutyrate (PHB). These findings highlighted the potential use of M. smegmatis for PHB production after further optimisation steps.