Screening of intestinal cellulose-degrading bacteria and comparison of enzyme activity in the Allomyrina dichotoma

Cellulosic biomass is the most widely distributed renewable resource on earth, and the screening of efficient cellulose-degrading bacterial strains is of great significance for the development and utilization of cellulosic biomass resources. We screened 58 cellulose-degrading bacteria from the 3^rd instar larvae of Allomyrina dichotoma by Congo red staining method, and selected the strain with larger ratio of transparent circle diameter to strain diameter for enzyme activity determination. Bacterial strain M24 was the strongest cellulase-producing strain by combining the results of Congo red staining method and enzyme activity determination. The filter paper enzyme, endoglucosidase, exoglucosidase and β-glucosidase with high activities of bacterial strain M24 were 13.14 U/mL, 45.67 U/mL, 18.29 U/mL and 36.30 U/mL, respectively. It was identified as Bacillus velezensis by comparison and analysis of 16S rDNA sequence. The whole genome sequence of the strain was obtained by genome ONT sequencing technology, which was 4290258 bp in length, with a total of 15 cellulase-related genes annotated, including 4 endo-β-1,4 glucanase genes (EC 3.2.1.4), 9 β-glucosidase (EC 3.2.1.91)-related genes, and 2 exo β-1,4 glucanase (EC 3.2.1.91)-related genes. This result provides an important theoretical basis and test material for constructing cellulose degradation engineering bacteria.