Role of outer membrane protein methylation in the process of bacterial environmental adaptation

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Bacterial environmental adaptation is a process whereby bacteria adapt to and survive within differing ecological niches. The bacterium Leptospira is a perfect model organism for studying the process of environmental adaptation, since more than 300 different strains of this bacterium have been identified. Some of these strains exist solely within aquatic locales and some are pathogenic strains that are able to survive within both animal hosts and aquatic environments. Despite this difference in growth location, most of the genes that encode proteins found on the outer membrane of the bacterium are conserved between pathogenic and environmental species, suggesting that factors other than protein presence or absence determine the environmental survival capability for this bacterium. During my previous NSERC Discovery grant we discovered a new outer membrane protein within Leptospira, which we designated OmpL32. To our surprise, we found that a methyl group was added to the glutamic acid residues within the protein in response to growth of the bacterium in different environmental conditions. Further exploration revealed that, of the Leptospira outer membrane proteins we identified in our studies, over 40% incorporated methyl groups in response to growth in changing environmental conditions. Our data show that the frequency of incorporation of methyl groups into outer membrane proteins is higher when this bacterium is growing within an animal host, and we suggest that this capability allows its survival within the host by changing the appearance of the bacterial surface so it is no longer recognized, and targeted, by the host's immune system. These studies will investigate a new mechanism of bacterial environmental adaptation that may constitute a general mechanism used by bacteria to enable survival in multiple environmental locales. These studies will therefore enhance our current understanding of the process of bacterial environmental adaptation and may reveal outer membrane protein methylation as a mechanism that could be specifically targeted for inhibition to prevent bacterial establishment within a particular environment.