Ott Brittany M, Dacks Andrew M, Ryan Kenneth J, Rio Rita V M
Department of Biology, West Virginia University, Morgantown, West Virginia, USA.
Department of Statistics, West Virginia University, Morgantown, West Virginia, USA.
Appl Environ Microbiol. 2016 Apr 18;82(9):2644-55. doi: 10.1128/AEM.00185-16. Print 2016 May.
Transmission, critical to the establishment and persistence of host-associated microbiotas, also exposes symbionts to new environmental conditions. With horizontal transmission, these different conditions represent major lifestyle shifts. Yet genome-wide analyses of how microbes adjust their transcriptomes toward these dramatic shifts remain understudied. Here, we provide a comprehensive and comparative analysis of the global transcriptional profiles of a symbiont as it shifts between lifestyles during transmission. The gammaproteobacterium Aeromonas veronii is transmitted from the gut of the medicinal leech to other hosts via host mucosal castings, yet A. veronii can also transition from mucosal habitancy to a free-living lifestyle. These three lifestyles are characterized by distinct physiological constraints and consequently lifestyle-specific changes in the expression of stress-response genes. Mucus-bound A. veronii had the greatest expression in terms of both the number of loci and levels of transcription of stress-response mechanisms. However, these bacteria are still capable of proliferating within the mucus, suggesting the availability of nutrients within this environment. We found that A. veronii alters transcription of loci in a synthetic pathway that obtains and incorporates N-acetylglucosamine (NAG; a major component of mucus) into the bacterial cell wall, enabling proliferation. Our results demonstrate that symbionts undergo dramatic local adaptation, demonstrated by widespread transcriptional changes, throughout the process of transmission that allows them to thrive while they encounter new environments which further shape their ecology and evolution.
传播对于宿主相关微生物群的建立和持续存在至关重要，同时也使共生体暴露于新的环境条件中。通过水平传播，这些不同的条件代表了主要的生活方式转变。然而，关于微生物如何针对这些巨大转变调整其转录组的全基因组分析仍未得到充分研究。在这里，我们提供了对一种共生体在传播过程中生活方式转变期间的全球转录谱的全面比较分析。维氏气单胞菌这种γ-变形菌通过宿主黏膜排泄物从药用水蛭的肠道传播到其他宿主，但维氏气单胞菌也可以从黏膜栖息状态转变为自由生活方式。这三种生活方式具有不同的生理限制，因此应激反应基因的表达也会有特定于生活方式的变化。就应激反应机制的基因座数量和转录水平而言，与黏液结合的维氏气单胞菌表达量最高。然而，这些细菌仍能够在黏液中增殖，这表明该环境中有营养物质可供利用。我们发现维氏气单胞菌会改变一条合成途径中基因座的转录，该途径获取N-乙酰葡糖胺（NAG；黏液的主要成分）并将其整合到细菌细胞壁中，从而实现增殖。我们的结果表明，共生体在整个传播过程中经历了显著的局部适应，这通过广泛的转录变化得以证明，使它们能够在遇到新环境时茁壮成长，而新环境又进一步塑造了它们的生态和进化。
