Bacillus velezensis SH-1471: optimization of fermentation conditions and evaluation of the biocontrol effect on tomato Fusarium wilt

Abstract:

[Objective] Bacillus velezensis SH-1471 (CCTCC No. M 2022923, Patent No. ZL 2022 1 1479280.X) is a strain that can control soil-borne diseases of crops and promote soil nutrient conversion and crop growth. This study aims to explore its potential biological activity and the optimum fermentation conditions, so as to promote the industrialization and commercial development of this strain.[Methods] A strain SH-1471 was identified based on the morphological, physiological, and biochemical characteristics and the 16S rRNA gene and gyrB-based phylogenetic trees. PCR was carried out to detect antibiotic synthesis genes in the strain. The inhibitory spectrum of the strain was measured by the plate confrontation assay and the fermentation liquid inhibition test. The abilities of the strain to produce enzymes, solubilize phosphorus and potassium, fix nitrogen, and secrete siderophores in vitro were measured. The fermentation conditions were optimized by single factor tests and response surface methodology with OD₆₀₀ value and inhibition rate as indicators. The growth-promoting effect of the fermentation liquid on tomato plants and the control effect of the fermentation liquid on tomato Fusarium wilt before and after optimization were determined by indoor pot experiments. [Results] Strain SH-1471 was identified as B. velezensis, carrying the antibiotic synthesis genes srfA, fenB, ituA, ituD, and bymA. It had strong antagonistic effects on 8 pathogenic microorganisms such as Fusarium oxysporum, Alternaria alternate, and Exserohilum turcicum. Moreover, the strain was capable of producing protease and cellulase, solubilizing phosphorus, fixing nitrogen, and secreting siderophores. The optimal medium formula for the fermentation of SH-1471 was composed of 17.92 g/L sucrose, 16.95 g/L soybean powder, 2.88 g/L magnesium sulfate, and 5.0 g/L yeast extract. The optimum fermentation conditions were pH 7.5, 33 ℃, 220 r/min, and 20–24 h. After optimization, the inhibition rate, OD₆₀₀, and potted control efficiency of the fermentation liquid reached 94.08% (increasing by 15.6%), 3.28 (increasing by 36.7%), and 93.8%, respectively. Moreover, strain SH-1471 significantly improved plant height, stem circumference, root length, root weight, and fresh weight and dry weight of the aboveground part of tomato seedlings. [Conclusion] B. velezensis SH-1471 carries rich genes for antibiotic synthesis, has the abilities of producing protease and cellulase, solubilizing phosphorus, fixing nitrogen, and secreting siderophores, and demonstrates strong inhibitory effects on a variety of pathogens. It can significantly reduce the incidence of tomato Fusarium wilt and improve the agronomic traits of tomato seedlings. Therefore, the strain has broad application prospects in the biocontrol of plant diseases and the promotion of plant growth.