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

细菌环境适应是细菌适应不同生态位并在其中生存的过程。钩端螺旋体细菌是研究环境适应过程的理想模式生物，因为已经鉴定了300多种不同的钩端螺旋体菌株。其中一些菌株只存在于水生场所，另一些是能够在动物宿主和水环境中生存的致病菌株。尽管生长位置存在差异，但编码细菌外膜上蛋白质的大多数基因在病原菌和环境物种之间是保守的，这表明除了蛋白质的存在或不存在外，其他因素决定了该细菌在环境中的生存能力。在我之前的NSERC发现拨款期间，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，我们发现蛋白质中的谷氨酸残基上添加了一个甲基，以响应细菌在不同环境条件下的生长。进一步的研究表明，在我们的研究中鉴定的钩端螺旋体外膜蛋白中，超过40%的蛋白含有甲基，以响应环境条件的变化。我们的数据显示，当这种细菌在动物宿主内生长时，甲基掺入外膜蛋白的频率较高，我们认为这种能力通过改变细菌表面的外观使其能够在宿主内生存，从而不再被宿主的免疫系统识别和靶向。这些研究将探索一种新的细菌环境适应机制，该机制可能构成细菌在多个环境地点生存的一般机制。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是一种可以特定靶向抑制的机制，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.