Studies on Physiological Ecology and Genetics of Hydrothermal Vent Sulfur Bacteria

最近发现的深海热液喷口（深度2000米）的动物群落表现出的生物量密度可能与地球上任何生态系统一样高。在这样的深度到达海底（苏斯，1980）。相反，化学自养细菌在当地生产的有机碳被认为形成了这些喷口的大部分或全部营养基础。在喷口，这些细菌中的一些是自由生活的，要么悬浮在热液羽流中，要么附着在表面上（Jannasch和Mottl, 1985; Jannasch, 1989）。它们为滤食动物和地表食草动物提供了食物来源。然而，在这种永久黑暗的环境中，细菌和动物之间维持生命的相互作用的主要部分发生在内共生关系中（由Childress等人回顾，1987）。在迄今为止研究的大多数例子中，共生体是某种类型的趋化自养硫细菌，但也已知甲烷氧化共生体（Cavanaugh等人，1987；Childress等人，1986）。化学自养硫细菌通过还原硫化合物（硫化物、单质硫、硫代硫酸盐等）的氧化产生能量（ATP或质子动力），通常通过卡尔文-本森循环固定二氧化碳，绿色植物和藻类也采用卡尔文-本森循环。共生体为其宿主提供营养的一般方式有两种。共生体可能保持完整，但过量产生某些有机物，这些有机物从共生体中泄漏出来或沉积在细胞外。或者，寄主可能使用溶酶降解一部分细菌，可能定位在液泡中。几乎没有证据表明这两种机制都在起作用。

Animal communities at the recently discovered deep Sea hydrothermal vents (depth 2000 m) exhibit biomass densities which are probably as high as any ecosystem on earth. As a matter reaches the sea floor at such depths (Suess, 1980). Instead, local production of organic carbon by chemoautotrophic bacteria is believed to form much or all of the nutritional base at these vents. At the vents some of these bacteria are free-living either suspended in hydrothermal plumes or attached to surfaces (Jannasch and Mottl, 1985; Jannasch, 1989). These offer food sources for filter feeding and surface grazing vent animals. In this permanently dark environment, however, the major portion of life-supporting interactions between bacteria and animals occurs in endosymbiotic associations (reviewed by Childress et al., 1987). In most examples studied to date the symbiont is some type of chemoautotrophic sulfur bacterium, but methane oxidizing symbionts are also known (Cavanaugh et al., 1987; Childress et al., 1986). Chemoautotrophic sulfur bacteria generate energy (ATP or a proton motive force) by the oxidation of reduced sulfur compounds (sulfide, elemental sulfur, thiosulfate, etc.) and usually fix CO2 via the Calvin- Benson cycle also employed by green plants and algae, There are two general ways a symbiont might provide nutrients to its host. The symbiont might remain intact but overproduce certain organics which leak out of the symbiont or be deposited extracellularly. Alternatively, the host might degrade a fraction of the bacteria using lytic enzymes, possibly localized in vacuoles. There is little evidence pointing to the operation of either mechanism.