Scheme: University Research Fellowship
Organisation: University of Oxford
Dates: Oct 2001-Sep 2009
Summary: Many bacteria that cause diseases of plants and animals use a molecular syringe known as a type III protein secretion system (T3SS) to inject proteins inside the cells of their host. These injected proteins disable the host immune system and allow bacteria to colonise host tissues. However, although T3SSs have primarily been studied in a clinical or agricultural context, it is increasingly evident that T3SSs are also present in environmental bacteria found in soil, water and on plant surfaces. Importantly, although these bacteria are typically non-pathogenic, the microbial community they belong to is an important source of bacterial pathogens that cause opportunistic infections of immune-suppressed patients. Thus, understanding the distribution and function of T3SS genes in environmental bacteria, and the ability of the proteins secreted by these bacteria to contribute to bacterial infection of plants or animals is of clinical, agricultural and scientific interest. We have studied the distribution and function of T3SSs in a group of bacteria known as the Pseudomonas fluorescens complex, which includes environmental bacteria and mushroom pathogenic bacteria. T3SS genes were observed to be present in many bacteria in the P. fluorescens complex, which was not surprising as we had previously detected T3SS genes in strains of P. fluorescens shown to have plant growth-promoting activity. However, unexpectedly, some mushroom pathogenic strains of P. fluorescens were found to contain as many as two or three different T3SS, resembling T3SS previously described in environmental, animal pathogenic and plant pathogenic bacteria, along with T3SS secreted proteins previously shown to be involved in bacterial infection of plants and animals. This suggests that P. fluorescens strains use T3SS-secreted proteins during infection of mushrooms, and during interactions with other organisms, and demonstrates that T3SSs are associated with a wide range of bacterial lifestyles.