Ecophysiology and Phylogeny of Diverse Beggiatoa Species, Bacterial Specialists of the Sulfide-Oxygen Interface

9513962 Nelson各种海洋沉积物的表面主要由无色的硫菌属和Beggiatoa属的硫菌组成。虽然这些细菌很少在纯培养物中生长，但最具特征的代表可以在氧-缺氧界面繁殖，那里有陡峭的硫化氢和氧梯度，硫化氢和氧分别可以作为它们的可氧化底物和氧化剂。有新的证据表明，这些细菌也是自养的，也就是说，它们可以以二氧化碳作为唯一的碳源合成细胞材料。在一些氧气很少或没有氧气的环境中，这些细菌的优势代表非常大，它们含有一个膜结合的中央液泡，大约占细胞体积的80%。这是唯一被报道具有这种结构的细菌。在来自三个不同地点的密集样本中，液泡形Beggiatoa和Thioploca最近被证明含有的硝酸盐浓度比其周围栖息地高10,000倍。该建议假设这些细菌使用这种内部硝酸盐作为终端电子受体，促进可溶性硫化物和/或有机化合物的呼吸。拟议的研究包括潜在电子供体（硫化物和有机物）和电子受体（硝酸盐和氧气）的原位消耗率的微电极和化学梯度分析。诊断酶的测定和使用放射性标记的有机和无机碳化合物的研究将有助于阐明这些化合物在其代谢中的相对作用。利用内部硝酸盐和产物的时间过程的研究，加上各种酶的测定，将测量这些细菌的反硝化能力。此外，在空间结构培养基中使用纯培养物，这些细菌利用有机和无机能量和碳源的相对比率仍有待评估。液泡状Beggiatoa被认为是富营养化海洋沉积物中剧烈的硫循环与氮循环之间重要联系的模型。如果它们和硫代菌被证明是反硝化菌，它们将成为第一个能够从海洋生态系统中去除组合氮的生态优势细菌。

9513962 Nelson The surfaces of a variety of marine sediments are dominated by colorless sulfur bacteria of the genera Thioploca and Beggiatoa. Although few of these bacteria have been grown in pure culture, the best characterized representatives can multiply at the oxic-anoxic interface where there are steep gradients of hydrogen sulfide and oxygen, which can serve as their oxidizable substrate and oxidant, respectively. There is emerging evidence that these bacteria are also autotrophs, i.e. they can synthesize their cell material starting with carbon dioxide as their sole carbon source. In some environments with little or no available oxygen, the dominant representatives of these bacteria are extremely large and they contain a membrane-bound central vacuole, comprising roughly 80% of cell volume. These are the only bacteria for which this structure has been reported. In dense samples from three different locations, vacuolate Beggiatoa and Thioploca were very recently demonstrated to contain nitrate in concentrations 10,000-fold higher than in their surrounding habitat. This proposal postulates that these bacteria use this internal nitrate as a terminal electron acceptor facilitating their respiration of soluble sulfide and/or organic compounds. Proposed studies include microelectrode and chemical gradient analysis of in situ consumption rates of potential electron donors (sulfide and organics) and electron acceptors (nitrate and oxygen). Assays of diagnostic enzymes and studies using radiolabelled organic and inorganic carbon compounds will help elucidate the relative roles of these compounds in their metabolism. Studies of the time-course of utilization of internal nitrate and the resultant products, coupled with various enzyme assays, will measure the capacity these bacteria have for denitrification. Additionally, using pure cultures in spatially structured cultu re media the relative rates by which these bacteria use organic and inorganic energy and carbon sources sill be assessed. Vacuolate Beggiatoa are proposed as a model of an important link between the vigorous sulfur cycle of eutrophic marine sediments and the nitrogen cycle. If they and Thioploca prove to be denitrifiers, they will be the first example of an ecologically dominant bacterium capable of removing combined nitrogen from a marine ecosystem.