Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106, USA.
J Exp Biol. 2011 Jan 15;214(Pt 2):312-25. doi: 10.1242/jeb.049023.
While chemoautotrophic endosymbioses of hydrothermal vents and other reducing environments have been well studied, little attention has been paid to the magnitude of the metabolic demands placed upon the host by symbiont metabolism and the adaptations necessary to meet such demands. Here we make the first attempt at such an evaluation, and show that moderate to high rates of chemoautotrophic or methanotrophic metabolism impose oxygen uptake and proton equivalent elimination demands upon the hosts that are much higher than is typical for the non-symbiotic annelid, bivalve and gastropod lineages to which they are related. The properties of the hosts are described and compared to determine which properties are associated with and predictive of the highest rates. We suggest that the high oxygen demand of these symbionts is perhaps the most limiting flux for the symbioses. Among the consequences of such demands has been the widespread presence of circulating and/or tissue hemoglobins in these symbioses that are necessary to support high metabolic rates in thioautotrophic endosymbioses. We also compare photoautotrophic with chemoautotrophic and methanotrophic endosymbioses to evaluate the differences and similarities in physiologies. These analyses suggest that the high demand for oxygen by chemoautotrophic and methanotrophic symbionts is likely a major factor precluding their endosymbiosis with cnidarians.
虽然热液喷口和其他还原环境中的化能自养内共生体已经得到了很好的研究，但对于共生体代谢对宿主施加的代谢需求的大小以及满足这些需求所需的适应机制，关注甚少。在这里，我们首次尝试对此进行评估，并表明适度到高的化能自养或甲烷营养代谢会给宿主带来比相关的非共生环节动物、双壳类和腹足类更高的氧气摄取和质子当量消除需求。描述了宿主的特性并进行了比较，以确定哪些特性与最高速率相关并具有预测性。我们认为，这些共生体的高耗氧量可能是共生关系中最具限制的通量。这些需求的后果之一是，在这些共生体中广泛存在循环和/或组织血红蛋白，这对于支持硫自养内共生体中的高代谢率是必要的。我们还比较了光合作用与化能自养和甲烷营养内共生体，以评估它们在生理学上的差异和相似之处。这些分析表明，化能自养和甲烷营养共生体对氧气的高需求可能是阻止它们与刺胞动物共生的主要因素。
