Identification of genetic factors affecting the survival of Legionella pneumophila in water systems

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Legionella pneumophila (Lp) causes the pneumonia Legionnaires' disease (LD). Incidence of LD is rather low, but it is increasing, and large outbreaks occur periodically in major cities worldwide during which hundreds of people can be infected. The mortality rate is typically around 10%. Lp is found in hot water distribution systems and cooling towers where it grows inside phagocytic protozoans. Transmission to humans occurs via aerosols. My long-term goals are to understand the genetic and environmental factors affecting the survival of bacterial pathogens in water systems and to develop strategies to enhance control of water-borne bacterial pathogens. Currently, chlorine and thermal treatments are used to control Lp in water systems. These treatments help reduce momentarily the population of Lp, and hence the transmission to humans, but fail to eliminate Lp. Presumably, Lp possesses response systems to survive such treatments, but not much is know about Lp's response to heat shock and chlorine. In addition, high level of genetic diversity between isolates and changes in Lp population structure in water systems over time suggest adaptation of Lp to specific conditions present in water systems and the treatment used. This is likely driven by point mutations and by acquisition of genes from resident microorganisms. Therefore, my short-term objectives for the next five years are to: 1) determine the transcriptional response of Lp to heat shock, 2) identify genes involved in the response of Lp to chlorine and heat shock, and 3) identify genetic adaptation of Lp during growth in complex water system undergoing periodic treatment.For the first objective, we will use a transcriptomic approach to study the role of regulators that we have previously identified to play a role in heat shock response. For the second objectives, a transposon-based approach will be used to identify genes required for surviving thermal treatment and chlorine disinfection. For the third objective, evolution experiments will be performed in pure water and in cooling tower microbiota to produce clones highly resistant to thermal treatment and chlorine compare to the ancestor strain. Genetic mutations and gene acquisitions associated with increased resistance will be identified by whole genome sequencing. My research plan describes a powerful approach that should shed lights on the genetic factors enabling Lp to resist control measures. This should help refine the strategies used to control the replication of Lp and other bacterial pathogens inside man-made water systems to prevent human infections. In addition, this work will contribute to our understanding of the evolution of Lp and other water-borne pathogens, particularly the role of horizontal gene transfer. During this research program, one MSc, 3 PhD and at least 5 undergraduate students will be trained in microbiology, molecular genetics, and bioinformatics.