Molecular mechanisms involved in Pseudomonas biocontrol

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Some bacteria naturally present in soil are able to inhibit the ability of fungi to cause disease in plants. As these bacteria do not cause disease in humans or other animals, they represent an environmentally friendly alternative to chemical pesticides. Sclerotinia sclerotiorum is a fungus that causes devastating losses in canola as well as over 400 other crop species. Work ongoing in the de Kievit laboratory is focused on a bacterium, Pseudomonas chlororaphis strain PA23 that it is able to control the growth of S. sclerotiorum and protect canola from the disease caused by this fungus. So far, the ability of biocontrol bacteria to act as substitutes for agrochemicals has not reached its full potential. Fluctuations in the expression of inhibitory compounds and failure of the introduced organism to establish itself in a given niche are two factors underlying poor performance. For biocontrol agents to be successful, we must understand the nature of the compound(s) required for disease inhibition as well as factors controlling their expression. In the research proposed, we will study how an essential regulator of gene expression, called PtrA, controls production of antibiotics and enzymes in PA23. Because several other bacteria contain ptrA-like genes, including bacteria that cause disease in humans, our findings are expected to have far-reaching implications. The ability of bacterial inoculants to cope with grazing predators is important for bacterial survival in the environment. Therefore, we will investigate how strain PA23 interacts with the bacterial-feeding roundworm, Caenorhabditis elegans. These studies will provide important information regarding bacteria-predator interactions.