Isolation and Functional Analysis of Rice Straw-Degrading Bacteria

Aiming at bottlenecks restricting straw-return resource utilization in global rice-planting regions, this study investigated soil microbial community structures of typical farmland soils from Guangdong Province in China. Proteobacteria, Acidobacteria and Bacillota were the dominant bacterial phyla, and Clostridium was the predominant genus. Predicted abundant glycoside hydrolase families (GH13, GH5, GH9) based on 16S rRNA gene sequencing provided an inherent microbial basis for lignocellulose degradation. Redundancy analysis and Linear Discriminant Analysis Effect Size (LEfSe) identified available phosphorus and total nitrogen as key environmental drivers, with Bacillus and Sphingomonas as habitat-indicator genera. Ten cellulose-degrading strains were isolated and taxonomically identified; Bacillus velezensis G-6 exhibited the highest carboxymethyl cellulase (CMCase) activity, and Bacillus licheniformis G-8 possessed the highest filter paper enzyme (FPase) activity. The majority of strains possessed multiple plant-growth-promoting characteristics, including the ability to synthesize siderophores and indole-3-acetic acid (IAA) and to solubilize phosphate. A 30-day straw-degradation assay indicated that compound microbial inoculant 2 with urea achieved the highest total straw degradation rate, while compound microbial inoculant 1 with urea showed the greatest cellulose degradation efficiency. This study supplies promising microbial resources and offers theoretical references for efficient rice straw incorporation, as well as the integrated application of microbial inoculants and nitrogen fertilization management within farmland ecosystems.