It is important to study the response of plant pathogens to the antibiosis traits of biocontrol microbes to design the efficient biocontrol strategies. In this study, we evaluated the role of volatile organic compounds (VOCs) produced by a biocontrol strain Bacillus amyloliquefaciens SQR-9 on the growth and virulence traits of tomato wilt pathogen Ralstonia solanacearum (RS). The VOCs of SQR-9 significantly inhibited the growth of RS on agar medium and in soil. In addition, the VOCs significantly inhibited the motility traits, production of antioxidant enzymes and exopolysaccharides, biofilm formation and tomato root colonization by RS. The strain SQR-9 produced 22 VOCs, but only nine VOCs showed 1–11% antibacterial activity against RS in their corresponding amounts; however, the consortium of all VOCs showed 70% growth inhibition of RS. The proteomics analysis showed that the VOCs of SQR-9 downregulated RS proteins related to the antioxidant activity, virulence, carbohydrate and amino acid metabolism, protein folding and translation, while the proteins involved in the ABC transporter system, amino acid synthesis, detoxification of aldehydes and ketones, methylation, protein translation and folding, and energy transfer were upregulated. This study describes the significance and effectiveness of VOCs produced by a biocontrol strain against tomato wilt pathogen.
Cong Huang,Qian Liu,Zhi-Ling Li,Xiao-dan Ma,Ya-Nan Hou,Nan-Qi Ren,Ai-Jie Wang
The denitrification desulfurization system can be used to remediate wastewater containing carbon, nitrogen, and sulfur. However, the relationship between autotrophic and heterotrophic bacteria remains poorly understood. To better understand the roles and relations of core bacteria, an expanded granular sludge bed (EGSB) reactor was continuously operated under autotrophic (stage I), heterotrophic (stage II) and mixotrophic (stages III–VII) conditions with a 490-day period. Stage IV represented the excellent S 0 recovery rate (69.5%). The different trophic conditions caused the obvious succession of dominant bacterial genera. Autotrophic environment (stage I) enriched mostly Thiobacillus , and heterotrophic environment (stage II) was dominated with Azoarcus and Pseudomonas. Thauera, Arcobacter and Azoarcus became the predominant genera under mixotrophic conditions (stage III-VII). Strains belonged to these core genera were further isolated, and all seven isolates were confirmed with denitrifying sulfur oxidation capacity. Heterotrophic strain HDD1 (genus of Thauera ) possessed both the highest sulfide degradation and S 0 recovery rates. Expression levels of cbbM and gltA genes were positively related with the autotrophic and heterotrophic conditions, respectively. NirK gene was highly expressed between log 3.7–log 4.3 during the entire run. Expression of both sqr and soxB genes were closely related with sulfur conversion. More than 57.5% of S 0 recovery rate could be obtained as sqr gene expression was greater than log 3.2, and while, sulfate was the primary form as soxB gene expression higher than log 3.9. The correlation between core microbial genera was very low from network, indicating a complex and non-specific mutualistic network between bacterial functional groups under each nutrient condition, and a stable coexistence state was possibly formed through utilizing each the secondary or waste metabolites in the mixotrophic conditions. This relationship was beneficial to the stability of the microbial community structure in the denitrification desulfurization system.
W. Raza,J. Yuan,Y. C. Wu,F. U. Rajer,Q. Huang,S. Qirong
The aim of the present study was to investigate the effects of the phytotoxin fusaric acid (FA) on the biocontrol traits of two biocontrol strains Paenibacillus polymyxa WR-2 and SQR-21. The results showed that the growth of both WR-2 and SQR-21 decreased with increasing FA concentration, and at 70 and 80 μ g mL −1 FA, respectively, the strains were unable to grow. The biocontrol traits of both strains were negatively affected by FA concentration higher than 2·5 μ g mL −1 . However, at 2·5 μ g mL −1 FA, biofilm formation and root colonization were not affected and there was even a positive effect on the production of spores and hydrolytic enzymes (protease and β -l,3-glucanase). The production of fusaricidin-type antifungal compounds was increased with an increase in FA concentration up to 50 and 60 μ g mL −1 for WR-2 and SQR-21, respectively. The production of antifungal volatile organic compounds by WR-2 and SQR-21 was increased only at 2·5 μ g mL −1 FA. The effect of FA on the overall metabolic activity of WR-2 and SQR-21 was also determined. This study will help to understand the response of P. polymyxa strains to FA and will help to improve their biocontrol efficiency.
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