Prospecting cellulolytic bacteria from white grubs (Holotrichia serrata (F.) and Leucopholis coneophora Burmeister) native to Karnataka region.

Abstract

The gut microbiota of insects plays a pivotal role in digesting food, supplying nutrients, and synthesizing enzymes, particularly those capable of degrading lignocellulosic biomass-a key factor in waste management. In Karnataka, India, the larvae of Holotrichia serrata and Leucopholis coneophora are major crop pests. However, the potential of their gut bacterial communities to degrade lignocellulose has yet to be fully explored. This study aimed to isolate and evaluate lignocellulose-degrading bacteria from these larvae. Seventeen cellulolytic bacterial strains were successfully isolated from the fermentation chamber of white grubs, most of which belonged to the Firmicutes and γ-Proteobacteria classes. Notable genera included Bacillus, Enterobacter, and Klebsiella. Among these, Bacillus toyonensis strain LC3B1 exhibited remarkable cellulolytic activity, with a cellulolytic index of 1.93 ± 0.037. This strain demonstrated the highest degradation on groundnut husk powder (33.25 ± 0.823%), followed by paddy straw powder (31.45 ± 0.608%) and corncob powder (28.15 ± 1.56%), highlighting its potential for effective agricultural residue degradation. FTIR analysis of carboxymethyl cellulose (CMC) hydrolyzed by LC3B1 revealed various decomposition products, including ketones, aldehydes, alcohols, and carboxylic acids. Scanning electron microscopy (SEM) of the treated biomass revealed significant morphological changes, such as pore formation and tunneling within the substrate. The broad cellulolytic capabilities observed across bacteria from white grub gut microbiota, including members of the Bacillaceae, Enterobacteriaceae, and Pseudomonadaceae families, underscore their potential as valuable resources for lignocellulosic biomass degradation, biofuel production, and sustainable waste management strategies. This study highlights the promise of insect gut microbiota as a reservoir for environmentally beneficial microbial applications.