Molecular identification and biological activity of three Bacillus strains isolated from an alpine meadow rhizosphere in Qinghai Province

For the purpose of restoring degraded vegetation and improving the aboveground biomass of grassland, the biological activity of three strains of Bacillus spp. bio-control agents were isolated and screened. Three strains isolated from an alpine meadow (Kobresia pygmaea) rhizosphere in Huangnan Autonomous Prefecture, Qinghai Province, were identified by 16S rDNA and gyrB partial sequence analyses. Antagonistic activity of strains to pathogenic fungi were determined by the flat confrontation test, and the growth-promoting activities of strains were checked by soaking plant seeds in strain suspension (106 cfu·mL-1 of cell concentration). In addition, cellulose-degrading activities of strains were checked with carboxymethylcellulose (CMC) plate test, Gram staining, and 3,5-dinitrosalicylic acid (DNS) methods; moreover, cellulase coding genes of the strains were amplified and analyzed. The results showed that the isolate of HNC3 was identified as Bacillus pumilus, and isolates of HNC8 and HNC11 were identified as B. thuringiensis. The three strains presented distinct antagonistic activity to Fusarium graminearum S and Fusarium oxysporum (inhibition zone diameter ≥ 11 mm). Furthermore, the strains showed obvious germination and growth-promoting activity after soaking the wheat seeds in Bacillus suspension. The effect of the isolate of HNC3 on the growth of wheat seedlings was significant; the rate of bud and root length growth increased by 55% and 80%, respectively. The cellulase activity of the isolate of HNC3 reached 367.51 U·mL-1, and its cellulase coding genes could be amplified including lichenase (blg1S), mannosidase (ManSig), and xylanase (xynD, xynB). The three Bacillus strains used as bio-control agents all showed antagonistic, plant growth-promoting, and cellulose-degrading activities, which present future research opportunities into the potential of their application in the recovery of plateau grassland vegetation, as well as in the field of ecological animal husbandry.