Evaluation of Cellulolytic Gut Bacteria Isolated from White Grubs (Holotrichia serrata and Leucopholis coneophora) and Their Utilization in Lignocellulose Degradation

Abstract The gut microbiota of insects plays a crucial role in digesting food, providing nutrients, and synthesizing enzymes. This approach is particularly relevant for degrading lignocellulosic biomass and managing waste. In Karnataka, the larvae of Holotrichia serrata and Leucopholis canephora are major crop pests, but the role of their bacterial communities in lignocellulose degradation has not been well studied. This study aimed to isolate and evaluate bacteria from these larvae for their ability to degrade lignocellulose.Approximately seventeen cellulolytic bacterial strains were isolated from the fermentation chamber of white grubs, primarily from the Firmicutes and γ-proteobacteria classes. Notable species included Bacillus, Enterobacter, and Klebsiella. Bacillus toyonensis strain LC3B1 demonstrated significant cellulolytic activity, with a cellulolytic index of 1.93 ± 0.037. The degradation of corncob powder was the highest (28.15 ± 1.56%), followed by that of paddy straw powder (31.45 ± 0.608%) and groundnut husk powder (33.25 ± 0.823%), indicating the strong ability of these powders to degrade agricultural residues. FTIR analysis of the substrate carboxymethyl cellulose (CMC) hydrolyzed by LC3B1 revealed decomposition products such as ketones, aldehydes, alcohols, and carboxylic acids. Scanning electron microscopy (SEM) revealed significant morphological changes and the formation of pores and tunnels in the treated biomass.The diverse cellulolytic capabilities of gut bacteria from white grubs, including those of the Bacillaceae, Enterobacteriaceae, and Pseudomonadaceae families, offer promising opportunities for lignocellulosic biomass degradation, biofuel production, and sustainable waste management.