Bacterial volatile organic compounds attenuate pathogen virulence via evolutionary trade-offs

Abstract

Volatile organic compounds (VOCs) produced by soil bacteria have been shown to exert plant pathogen biocontrol potential owing to their strong antimicrobial activity. While the impact of VOCs on soil microbial ecology is well established, their effect on plant pathogen evolution is yet poorly understood. Here we experimentally investigated how plant-pathogenic Ralstonia solanacearum bacterium adapts to VOC-mixture produced by a biocontrol Bacillus amyloliquefaciens T-5 bacterium and how these adaptations might affect its virulence. We found that VOC selection led to a clear increase in VOC-tolerance, which was accompanied with cross-tolerance to several antibiotics commonly produced by soil bacteria. The increasing VOC-tolerance led to trade-offs with R. solanacearum virulence, resulting in almost complete loss of pathogenicity in planta. At the genetic level, these phenotypic changes were associated with parallel mutations in genes encoding lipopolysaccharide O-antigen (wecA) and type-4 pilus biosynthesis (pilM), which both have been linked with outer membrane permeability to antimicrobials and plant pathogen virulence. Reverse genetic engineering revealed that both mutations were important, with pilM having a relatively larger negative effect on the virulence, while wecA having a relatively larger effect on increased antimicrobial tolerance. Together, our results suggest that microbial VOCs are important drivers of bacterial evolution and could potentially be used in biocontrol to select for less virulent pathogens via evolutionary trade-offs.

Broad‐spectrum antagonistic potential of Bacillus spp. volatiles against Rhizoctonia solani and Xanthomonas oryzae pv. oryzae

“…The Bacillus VOCs assay showed that these strains, FZB42, NMTD17, and LLTC93‐VOCs, had higher antifungal activity against R. solani and antibacterial activity of Xoo compared to control. Similarly, certain VOCs against R. solani and R. solanacearum were evaluated using the Bacillus VOCs previously identified through GC–MS (Guo et al, 2023; Wang et al, 2023). The synthetic VOCs, PDC, BDH, 1,2‐BIT, and MIX‐VOCs were explored, indicating strong antimicrobial activity against R. solani and Xoo diseases.…”

“…Briefly, the VOC mixture was prepared by mixing three individual VOC compounds in the same ratio as they are produced by selected Bacillus spp. after 3 days of growth in the LB (Wang et al, 2023). Different concentrations (5, 10, 20, 40, and 80 μg mL −1 ) of synthetic VOCs were prepared from their respective stock solutions (1 mg mL −1 ) for their antimicrobial potential.…”

“…Briefly, the VOC mixture was prepared by mixing three individual VOC compounds in the same ratio as they are produced by selected Bacillus spp. after 3 days of growth in the LB (Wang et al, 2023). Different concentrations (5, 10, 20, 40, and et al 2021).…”

“…Pentadecane (PDC) produced by Bacillus zhangzhouensis LLTC93, Benzaldehyde (BDH), emitted by B. velezensis FZB42, and 1,2-Benz isothiazol-3(2H)-one (1,2-BIT) produced by Bacillus artrophaeus LSSC22, and MIX-VOCs were used to determine antimicrobial activity. The selected VOCs were used to prepare the VOC mixture according to the previously described by (Wang et al 2023). Briefly, the VOC mixture was prepared by mixing three individual VOC compounds in the same ratio as they are produced by selected Bacillus spp.…”

Microbial Consortia for Plant Protection against Diseases: More than the Sum of Its Parts

“…Interestingly, the activity of these volatile compounds extends beyond growth inhibition, as they can modulate Ralstonia metabolism to suppress virulence [108]. Furthermore, it has been observed that R. solanacearum could acquire resistance to the volatiles produced by Bacillus amyloliquefaciens T-5 but will lose the virulence factors responsible for its pathogenicity [109]. This phenomenon can alter the plant pathogen evolution toward decreased virulence.…”