Optimization of fermentation conditions for Bacillus velezensis TCS001 and evaluation of its growth promotion and disease prevention effects on strawberries

Abstract

• Optimized fermentation medium with carbon and nitrogen sources: 2.89% peanut cake powder, 3.0% glucose, and 3.0% soluble starch. • Optimized cultural conditions: temperature 28 °C, rotation speed 173 r/min, inoculation volume 1 %, filling volume 31 % (77.5 mL / 250 mL), pH 7.0. • B. velezensis TCS001 was shown to have promoted the growth of strawberry plants and exhibited effective control over anthracnose. Bacillus velezensis TCS001 is a novel biocontrol bacterium with broad-spectrum antimicrobial activity and plant growth-promoting effects, holding great potential for development in agricultural production. This study optimized the fermentation conditions for B. velezensis TCS001 through single-factor experiments combined with response surface methodology, and developed a formulation for TCS001 suspension concentrate (TCS001-SC). The efficacy of TCS001-SC to promote the growth of strawberries and to prevent and control strawberry anthracnose was evaluated. The optimal liquid fermentation condition for TCS001 was determined to be 2.89 % soluble peanut meal powder, 3.0 % glucose, 3.0 % soluble starch, 0.002 % FePO 4 , 0.006 % KCl, 0.6 % NaCl, 0.05 % MgCl 2 ·6H 2 O, 0.3 % K 2 HPO 4 , 0.15 % KH 2 PO 4 , 0.05 % CaCO 3 , 0.005 % MnSO 4 , a working volume of 31 % (77.5 mL/250 mL), a rotation speed of 173 r/min, a cultivation temperature of 28°C, an inoculation volume of 1.0 %, and a pH of 7.0. Under which, the spore counts in the shake flask and 15 L fermenter fermentation broth were 6.70 × 10 9 CFU/mL and 9.46 × 10 9 CFU/mL, respectively, which were 1.48 and 2.01 times the spore count of 4.70 × 10 9 CFU/mL before optimization, utilizing a 15 L fermenter, the fermentation process was completed, and the resulting broth was preliminarily formulated into TCS001-SC. TCS001 live culture inhibited the mycelial growth of five different anthracnose fungi significantly with inhibition rates ranged from 70.3 % to 87.2 %. TCS001-SC promoted the growth of strawberries and induced rapid production of defensive enzymes in the leaves, enhancing plant resistance to pathogens. Specifically, after a 300-fold dilution spray treatment, the number of leaves, fresh weight of stems and leaves, fresh weight of roots, POD activity, and GA content of individual strawberry plants increased by 26.5 %, 79.4 %, 120 %, 23.24 %, and 32.61 %, respectively, compared to the control. After a 300-fold dilution root drench treatment, the leaf area, plant height, SOD activity, CAT activity, IAA content, and ABA content of strawberries increased by 68.41 %, 29.68 %, 21.49 %, 21.22 %, 38.64 %, and 36.04 %, respectively. The treatment also showed good prevention and control effects against anthracnose disease in strawberries, with the efficacy increasing as the number of spray applications increased. The control efficacy after five applications of TCS001-SC at a concentration of 2 × 10 7 CFU/mL was 60.45 %, which was comparable to the commercial wettable powder of B. subtilis , subsequent field trials will be conducted to determine its potential as a microbial pesticide. This study provides important support for the future industrial production and application of the strain TCS001.

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