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

细菌的环境适应是细菌适应并生存于不同生态位的过程。 钩端螺旋体是研究环境适应过程的理想模式生物，因为已经鉴定了300多种不同的这种细菌菌株。 这些菌株中的一些仅存在于水生环境中，而一些是能够在动物宿主和水生环境中存活的致病菌株。 尽管在生长位置上存在这种差异，但在细菌外膜上发现的编码蛋白质的大多数基因在致病性和环境物种之间是保守的，这表明蛋白质存在或不存在以外的因素决定了这种细菌的环境生存能力。 在我之前的NSERC发现资助期间，我们在钩端螺旋体中发现了一种新的外膜蛋白，我们将其命名为OmpL32。 令我们惊讶的是，我们发现蛋白质内的谷氨酸残基中添加了一个甲基，以响应细菌在不同环境条件下的生长。 进一步的探索表明，在我们的研究中鉴定的钩端螺旋体外膜蛋白中，超过40%的甲基结合在变化的环境条件下响应生长。 我们的数据表明，当这种细菌在动物宿主中生长时，甲基基团掺入外膜蛋白的频率更高，我们认为这种能力通过改变细菌表面的外观使其在宿主中存活，因此它不再被宿主的免疫系统识别和靶向。 这些研究将探讨细菌环境适应的新机制，这可能构成细菌在多个环境场所生存的一般机制。 因此，这些研究将增强我们目前对细菌环境适应过程的理解，并可能揭示外膜蛋白甲基化作为一种机制，可以特异性地靶向抑制，以防止细菌在特定环境中建立。

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.