Biotransformation of Lignocellulosic Biomass Hydrolysate into Polyhydroxybutyrate Biopolymer via Ralstonia Eutropha
Authors: Jaffur Nausheen , Jeetah Pratima , Kumar Gopalakrishnan 
Published: September 2023

Currently, a rampant cultural shift is occurring in the modern world to progressively substitute fossil-derived plastics and shift to novel biomaterials that are benign to the environment owing to increased awareness of environmental sustainability along with the implementation of strict regulations worldwide. Polyhydroxyalkanoates (PHAs) are promising intracellular biodegradable polymers that have attracted considerable focus owing to their biocompatibility, biodegradability, non-toxicity and environment-friendly nature to function in diverse applications notably in the pharmaceutical, medical, textile, materials, fuel, agricultural industries. Nonetheless, despite its huge market potential, the commercial growth of PHA is achieved on a small extent only, since the cost-effectiveness of this product is highly debatable owing to the high production cost of processing the carbon substrate. The goal behind this research study is to explore the possibility of exploiting low-cost carbon substrates from low-value lignocellulosic materials that would have otherwise been discarded as waste and add stress to the landfill to manufacture biopolymer compounds that are used in everyday lives as well as to enhance the functionality and yields of glucose from PHA substrates that can undergo industrial upscaling. One of the major challenges of transforming lignocellulosic biomass into fermentable sugars is the recalcitrant nature of the fibre which renders it very resistant to the release of sugars for fermentation. Since lignocellulosic biomass has a specific attribute such as an extremely coordinated matrix which renders it very resistant to the release of sugars for fermentation owing to biological degradation, a pre-treatment phase is necessary prior to the hydrolysis stage for the transformation of the fermentable sugars. This study focuses on the biosynthesis of biopolymers from lignocellulosic biomass through sustainable approaches such as enzyme and microbial activities in order to examine its viability as a replacement for traditional polymers. Cupriavidus Necator H16 (Ralstonia Eutropha) having 8×108 CFU/ml viable colonies were cultured at 30 oC and was inoculated in submerged fermentation of M9 minimal salt medium using 1% reducing sugar from Furcraea Foetida as carbon source. Batch fermentation of PHB in submerged cultivation conducted for a residence time from 0 to 48h resulted in a dry cell weight from 0.32±0.05% to 1.62±0.05%. The nitrogen limiting phase was achieved after 48h and 17.05±0.35% of PHB was extracted from 3ml of the fermentation broth. The PHB yield was dramatically lower than reported optimal yields of 37.55 to 97.80% from works of literature. Nonetheless, Fourier-transform infrared spectroscopy (FTIR) spectroscopy revealed characteristics bands for carbonyl, methine and ester groups along with intermolecular hydrogen bonds in the biopolymer. Sudan Black B and FTIR spectrum demonstrate that PHB biosynthesis successfully bioaccumulates inside the cells of Ralstonia Eutropha using cellulose from Lignocellulosic biomass (LCB) as carbon source. Hence, the process needs to be optimized in terms of variables such as inoculum size, inoculum concentration, incubation time and salt medium conditions in order to maximise the production of PHB from Furcraea Foetida in Ralstonia Eutropha cultivation.