Characterization of lignin and hemicellulose degrading bacteria isolated from cow rumen and forest soil: Unveiling a novel enzymatic model for rice straw deconstruction.

Application of greener pretreatment technology using robust ligninolytic bacteria for short duration to deconstruct rice straw and enhance bioethanol production is currently lacking. The objective of this study is to characterize three bacterial strains isolated from the milieux of cow rumen and forest soil and explore their capabilities of breaking down lignocellulose - an essential process in bioethanol production. Using biochemical and genomic analyses these strains were identified as Bacillus sp. HSTU-bmb18, Bacillus sp. HSTU-bmb19, and Citrobacter sp. HSTU-bmb20. Genomic analysis of the strains unveiled validated model hemicellulases, multicopper oxidases, and pectate lyases. These enzymes exhibited interactions with distinct lignocellulose substrates, further affirmed by their stability in molecular dynamic simulations. A comprehensive expression of ligninolytic pathways, including ß-ketoadipate, phenyl acetate, and benzoate, was observed within the HSTU-bmb20 genome. The strains secreted approximately 75-82 U/mL of cellulase, xylase, pectinase, and lignin peroxidase. FT-IR analysis of the bacterial treated rice straw fibers revealed that the intensity of lignin-related peaks decreased, while cellulose-related peaks sharpened. The values of crystallinity index for the untreated control and the treated rice straw with either HSTU-bmb18, or HSTU-bmb19, or HSTU-bmb20 were recorded to be 34.48, 28.49, 29.36, 31.75, respectively, which are much higher than that of 13.53 noted for those treated with the bacterial consortium. The ratio of fermentable cellulose in rice straw increased by 1.25-, 1.79-, 1.93- and 2.17-fold following treatments with HSTU-bmb18, HSTU-bmb20, HSTU-bmb19, and a mixed consortium of these three strains, respectively. These aggregative results suggested a novel model for rice straw deconstruction utilizing hydrolytic enzymes of the consortium, revealing superior efficacy compared to individual strains, and advancing cost-effective, affordable, and sustainable green technology.

Unveiling lignocellulolytic trait of a goat omasum inhabitant Klebsiella variicola strain HSTU-AAM51 in light of biochemical and genome analyses.

Klebsiella variicola is generally known as endophyte as well as lignocellulose-degrading strain. However, their roles in goat omasum along with lignocellulolytic genetic repertoire are not yet explored. In this study, five different pectin-degrading bacteria were isolated from a healthy goat omasum. Among them, a new Klebsiella variicola strain HSTU-AAM51 was identified to degrade lignocellulose. The genome of the HSTU-AAM51 strain comprised 5,564,045 bp with a GC content of 57.2% and 5312 coding sequences. The comparison of housekeeping genes (16S rRNA, TonB, gyrase B, RecA) and whole-genome sequence (ANI, pangenome, synteny, DNA-DNA hybridization) revealed that the strain HSTU-AAM51 was clustered with Klebsiella variicola strains, but the HSTU-AAM51 strain was markedly deviated. It consisted of seventeen cellulases (GH1, GH3, GH4, GH5, GH13), fourteen beta-glucosidase (2GH3, 7GH4, 4GH1), two glucosidase, and one pullulanase genes. The strain secreted cellulase, pectinase, and xylanase, lignin peroxidase approximately 76-78 U/mL and 57-60 U/mL, respectively, when it was cultured on banana pseudostem for 96 h. The catalytically important residues of extracellular cellulase, xylanase, mannanase, pectinase, chitinase, and tannase proteins (validated 3D model) were bound to their specific ligands. Besides, genes involved in the benzoate and phenylacetate catabolic pathways as well as laccase and DiP-type peroxidase were annotated, which indicated the strain lignin-degrading potentiality. This study revealed a new K. variicola bacterium from goat omasum which harbored lignin and cellulolytic enzymes that could be utilized for the production of bioethanol from lignocelluloses.