Simultaneous saccharification and fermentation using lignocellulolytic microorganisms and Zymomonas mobilis for bioethanol production from paddy straw

This study explores the optimization of bioethanol production from paddy straw using Zymomonas mobilis along with lignocellulolytic microorganisms such as, Bacillus inaquosorum, Phanerochaete chrysosporium and Streptomyces viridosporus. This research focused on thermochemical pretreatment methods like acid, alkali and hydrothermal processes to enhance the release of reducing sugars for fermentation. Most of the previous studies have focused on the use of purified enzymes for the release of reducing sugars from biomass, while this study intends to use the lignocellulolytic microorganisms as such. Physicochemical analysis of the paddy straw revealed a neutral detergent fiber (NDF) content of 71.5%, an acid detergent fiber (ADF) content of 51.2%, a bulk density of 0.16 g cc⁻¹ and a moisture content of 3%. Among the pretreatments, alkaline-assisted hydrothermal pretreatment resulted in the highest total reducing sugars (TRS) yield, reaching 2,695 µg g⁻¹ biomass after 3 h of incubation. Scanning electron microscopy (SEM) and fourier-transform infrared spectroscopy (FTIR) confirmed significant structural changes in the biomass, enhancing its enzyme accessibility. Simultaneous saccharification and fermentation (SSF) was employed to convert these sugars into ethanol. The highest ethanol yield of 2.12% was achieved using a microbial consortium of Zymomonas mobilis and lignocellulolytic organisms after 120 h of fermentation. These findings highlight the potential of paddy straw as a sustainable bioethanol feedstock, contributing to environmental sustainability and reducing reliance on fossil fuels.

Graphical Abstract