Screening, identification, and genome-wide analysis of a straw-degrading strain of Bacillus subtilis

Abstract:

[Background] Increasing the straw degradation efficiency is a key path to improve soil quality and curbing soil degradation. [Objective] To screen out the strains with strong degradation effect on straw, optimize the culture conditions and mine the functional genes of the strain. [Methods] Soil samples were collected from a low-temperature and arid area in northern China. The hydrolysis circle assay, cell density assay, and enzyme activity measurement were employed to screen the isolates and characterize the strain screened out. Field degradation experiments were carried out, and functional genes of the strain were mined by whole genome sequencing. [Results] Bacillus stercoris HS6-2 with strong stress tolerance was isolated. In the field, this strain showed the straw degradation rates of 55.74% and 84.77% after rooting for 30 and 180 days, respectively, which were 25.2% and 11.99% higher than those in the control. Under the optimized conditions, the strain showed the endo-cellulase, exo-cellulase, and filter paper enzyme activities of 3.63, 12.27, and 3.48 U/mL, respectively. The results of whole genome sequencing showed that the CAZy family members were encoded by 189 genes, including 71 glycoside hydrolases, some of which were involved in lignocellulose degradation. [Conclusion] HS6-2 as a mildly halophilic and basophilic strain with tolerance to drought and low temperatures demonstrates good application potential in straw degradation, which provides technical support for the research and development of microbial agents serving straw returning.

Key words:straw-degrading microorganisms;Bacillus subtilis;stress tolerance;fermentation optimization;whole genome