CNRS, UMR 7144, Adaptation et Diversité en Milieu Marin, Station Biologique de Roscoff, 29682 Roscoff, France.
BMC Genomics. 2011 Oct 28;12:530. doi: 10.1186/1471-2164-12-530.
The deep-sea hydrothermal vent mussel Bathymodiolus azoricus harbors thiotrophic and methanotrophic symbiotic bacteria in its gills. While the symbiotic relationship between this hydrothermal mussel and these chemoautotrophic bacteria has been described, the molecular processes involved in the cross-talking between symbionts and host, in the maintenance of the symbiois, in the influence of environmental parameters on gene expression, and in transcriptome variation across individuals remain poorly understood. In an attempt to understand how, and to what extent, this double symbiosis affects host gene expression, we used a transcriptomic approach to identify genes potentially regulated by symbiont characteristics, environmental conditions or both. This study was done on mussels from two contrasting populations.
Subtractive libraries allowed the identification of about 1000 genes putatively regulated by symbiosis and/or environmental factors. Microarray analysis showed that 120 genes (3.5% of all genes) were differentially expressed between the Menez Gwen (MG) and Rainbow (Rb) vent fields. The total number of regulated genes in mussels harboring a high versus a low symbiont content did not differ significantly. With regard to the impact of symbiont content, only 1% of all genes were regulated by thiotrophic (SOX) and methanotrophic (MOX) bacteria content in MG mussels whereas 5.6% were regulated in mussels collected at Rb. MOX symbionts also impacted a higher proportion of genes than SOX in both vent fields. When host transcriptome expression was analyzed with respect to symbiont gene expression, it was related to symbiont quantity in each field.
Our study has produced a preliminary description of a transcriptomic response in a hydrothermal vent mussel host of both thiotrophic and methanotrophic symbiotic bacteria. This model can help to identify genes involved in the maintenance of symbiosis or regulated by environmental parameters. Our results provide evidence of symbiont effect on transcriptome regulation, with differences related to type of symbiont, even though the relative percentage of genes involved remains limited. Differences observed between the vent site indicate that environment strongly influences transcriptome regulation and impacts both activity and relative abundance of each symbiont. Among all these genes, those participating in recognition, the immune system, oxidative stress, and energy metabolism constitute new promising targets for extended studies on symbiosis and the effect of environmental parameters on the symbiotic relationships in B. azoricus.
深海热液喷口贻贝 Bathymodiolus azoricus 的鳃中栖息着硫氧化和甲烷氧化共生细菌。虽然这种热液贻贝与其化能自养细菌之间的共生关系已被描述，但共生体之间的分子相互作用过程、共生体的维持、环境参数对基因表达的影响以及个体之间的转录组变化仍知之甚少。为了了解这种双重共生关系是如何以及在多大程度上影响宿主基因表达，我们使用转录组学方法来鉴定可能受共生体特征、环境条件或两者共同调控的基因。这项研究是在来自两个截然不同种群的贻贝上进行的。
消减文库鉴定出约 1000 个可能受共生和/或环境因素调控的基因。微阵列分析显示，120 个基因（所有基因的 3.5%）在梅内兹·格温（MG）和彩虹（Rb）喷口场之间存在差异表达。在共生体含量高的贻贝和共生体含量低的贻贝之间，受调控基因的总数没有显著差异。就共生体含量的影响而言，MG 贻贝中只有 1%的基因受硫氧化（SOX）和甲烷氧化（MOX）细菌含量的调控，而在 Rb 贻贝中则有 5.6%的基因受调控。在两个喷口场中，MOX 共生体也比 SOX 调控更多比例的基因。当根据共生体基因表达分析宿主转录组表达时，它与每个喷口场中的共生体数量有关。
我们的研究初步描述了热液喷口贻贝宿主中同时存在硫氧化和甲烷氧化共生细菌的转录组反应。该模型有助于鉴定参与共生体维持或受环境参数调控的基因。我们的结果提供了共生体对转录组调控影响的证据，并且差异与共生体类型有关，尽管涉及的基因比例仍然有限。在喷口场之间观察到的差异表明，环境强烈影响转录组调控，并且影响每个共生体的活性和相对丰度。在所有这些基因中，那些参与识别、免疫系统、氧化应激和能量代谢的基因构成了对 B. azoricus 共生关系以及环境参数对共生关系影响的进一步研究的新的有希望的靶标。
