Department of Medical Microbiology and Immunology, University of Wisconsin, Madison, WI 53706, USA.
Proc Natl Acad Sci U S A. 2010 Feb 2;107(5):2259-64. doi: 10.1073/pnas.0909712107. Epub 2010 Jan 19.
Mechanisms for controlling symbiont populations are critical for maintaining the associations that exist between a host and its microbial partners. We describe here the transcriptional, metabolic, and ultrastructural characteristics of a diel rhythm that occurs in the symbiosis between the squid Euprymna scolopes and the luminous bacterium Vibrio fischeri. The rhythm is driven by the host's expulsion from its light-emitting organ of most of the symbiont population each day at dawn. The transcriptomes of both the host epithelium that supports the symbionts and the symbiont population itself were characterized and compared at four times over this daily cycle. The greatest fluctuation in gene expression of both partners occurred as the day began. Most notable was an up-regulation in the host of >50 cytoskeleton-related genes just before dawn and their subsequent down-regulation within 6 h. Examination of the epithelium by TEM revealed a corresponding restructuring, characterized by effacement and blebbing of its apical surface. After the dawn expulsion, the epithelium reestablished its polarity, and the residual symbionts began growing, repopulating the light organ. Analysis of the symbiont transcriptome suggested that the bacteria respond to the effacement by up-regulating genes associated with anaerobic respiration of glycerol; supporting this finding, lipid analysis of the symbionts' membranes indicated a direct incorporation of host-derived fatty acids. After 12 h, the metabolic signature of the symbiont population shifted to one characteristic of chitin fermentation, which continued until the following dawn. Thus, the persistent maintenance of the squid-vibrio symbiosis is tied to a dynamic diel rhythm that involves both partners.
控制共生体种群的机制对于维持宿主与其微生物伙伴之间的联系至关重要。我们在这里描述了鱿鱼 Euprymna scolopes 和发光细菌 Vibrio fischeri 之间共生关系中存在的昼夜节律的转录、代谢和超微结构特征。这种节律是由宿主每天黎明时分从发光器官中排出大部分共生体种群驱动的。在这个每日周期的四个时间点，我们对支持共生体的宿主上皮组织和共生体种群本身的转录组进行了特征描述和比较。两个伙伴的基因表达最大波动发生在白天开始时。最值得注意的是，宿主中有>50 个与细胞骨架相关的基因在黎明前上调，随后在 6 小时内下调。通过 TEM 检查上皮组织，发现了相应的重构，其特征是顶端表面的消失和起泡。在黎明时排出后，上皮组织重新建立了极性，残留的共生体开始生长，重新填充发光器官。对共生体转录组的分析表明，细菌通过上调与甘油厌氧呼吸相关的基因来应对消失；支持这一发现的是，对共生体膜的脂质分析表明直接掺入了宿主来源的脂肪酸。12 小时后，共生体种群的代谢特征转变为特征性的几丁质发酵，一直持续到下一个黎明。因此，鱿鱼-弧菌共生关系的持续维持与涉及两个伙伴的动态昼夜节律有关。
