A new study by Chernin et al. has found that volatile organic compounds produced by certain Plant Growth Promoting Rhizobacteria (PGPR) can disrupt bacterial cell-cell communication (quorum sensing) in a number of plant pathogens including Agrobacterium, Chromobacterium, Pectobacterium and Pseudomonas. Application of PGPRs could in future be used as a new disease management strategy.
Quorum sensing was first discovered in two marine bacteria Vibrio fischeri and Vibrio harveyi. Here, individual bacteria sense the presence of other members by secreting chemical molecules into the environment. Sufficiently high amounts of these molecules in the surrounding would thus suggest a high population and trigger certain population dependent activities. In these bio-luminous bacteria for example, the production of light is triggered at high population density.
Following this initial discovery, quorum-sensing was found to exist in many bacteria including animal and plant pathogens. In pathogens, processes critical for pathogenicity were found to be triggered in a population dependent manner. In Erwinia caratovora, the causal agent of soft rot in potato for example, the bacteria produce enzymes to macerate the host (and draw nutrients) only when present in sufficiently high numbers. This prevents early recognition of the bacteria by the plant’s defense systems which could have in turn prevented disease.
Chernin L. et al. recently showed that certain Plant Growth Promoting Rhizobacteria (PGPR) are capable of producing volatile compounds that can reduce (quench) the signal molecules of pathogens. Specifically, they found that volatile organic compounds produced by strains of Pseudomonas fluorescens and Serratia plymuthica can disrupt quorum sensing in a number of plant pathogens including Agrobacterium, Chromobacterium, Pectobacterium and Pseudomonas. Since PGPRs are used as agricultural inputs in many crops, ‘quorum-quenching’ could serve as a new disease management strategy.
The potential of this tool was further broadened when Gadoury et al., suggested a similar quorum-sensing mechanism to exist in the grape powdery mildew pathogen Erysiphe necator. Here, the authors indicate that production of spores (conidia) is triggered only after the fungus has grown some amount of mycelium and suggested the role of quorum sensing in triggering this conidiation. This is the first suggestion of quorum-sensing in fungal plant pathogens.
Although, the use of quorum sensing disruption techniques as a tool for disease management is still in its infancy, the potential applications of this idea are truly fascinating.
- Chernin, L., Toklikishvili, N., Ovadis, M., Kim, S., Ben-Ari, J., Khmel, I. and Vainstein, A. (2011), Quorum-sensing quenching by rhizobacterial volatiles. Environmental Microbiology Reports, 3: 698–704. doi: 10.1111/j.1758-2229.2011.00284.x
- Gadoury, D. M., Wakefield, L. M., Cadle-Davidson, L., Dry, I. B., and Seem, R. C. 2012. Effects of prior vegetative growth, inoculum density, light, and mating on conidiation of Erysiphe necator. Phytopathology 102:65-72. DOI: 10.1094/PHYTO-03-11-0085