Bioethanol Production from Lignocellulosic Waste Without Pre-treatment Employing Vermicompost and Earthworm Gut-isolated Bacteria: Insights on Waste to Wealth Conversion Efficiency Towards Cleaner Lifestyle

Lignocellulosic wastes (LCW) have enormous potential to be recycled for bioethanol production. Although yeasts (Saccharomyces sp.) are commonly used bio-agents for fermentation, their efficiency is inhibited in cellulosic feedstocks. This study isolated novel ethanologenic bacteria from vermicomposting systems for bioenergy generation from fruit waste without pre-treatment. Initially, six strains out of 22, showing remarkable ethanol production ability, were characterized via 16S rRNA sequencing. Specifically, two strains (Bacillus alcalophilus C5 and Rhizobium spp. S10) produced more ethanol (5.5 and 15.7 g L⁻¹) than the yeast (5 g L⁻¹) from banana epicarps. These strains' dramatically high sedimentation rate and ethanol tolerance strongly justified their industrial applicability. Significant upregulation of alcohol dehydrogenase and acetyl CoA synthase endowed greater ethanol-producing capacity in C5 and S10 than in S. cerevisiae. The flow cytometry and confocal microscopy evidenced that ethanologenic bacteria uniquely defend the reactor-induced sugar and ethanol stresses through reverse/delayed apoptosis and robust membrane integrity. The waste-to-wealth conversion efficiency and cost–benefit analyses estimated that bacteria-mediated LCW-to-bioethanol conversion was a more profitable venture than vermicomposting or composting. Overall, this research demonstrated that the C5 and S10 isolates were more effective than widely used commercial yeast strains for bioethanol generation from LCW. Graphical Abstract: (Figure presented.)