Ecophysiology of Vacuolate Marine Sulfur Bacteria

大型的、真空的、积累硝酸盐的细菌，如Beggiatoa，可以氧化各种海洋生态位中产生的大部分硫化物。与硫磺细菌密切相关的细菌(液泡化附着的细丝或VAF)不积累硝酸盐，在海洋硫化物喷口的表面上大量存在。总体而言，这些在系统发育上一致的生物是已知的唯一含有液泡的变形杆菌，显然它们在各种海洋环境的氮和硫循环中发挥着重要作用。Beggiatoa物种也是被称为“黑带病”的细菌联合体的成员，这种细菌构成了一种广泛而致命的珊瑚疾病。首席研究人员从黑带病(菌株BBD)中分离出一株直径7微米的空泡状Beggiatoa菌株，该菌株积累硝酸盐，似乎能够固定氮素。该培养菌株以及VAF和积累硝酸盐的Beggiatoa的一些自然种群是该项目的重点。研究人员将使用微电极和分子分析来了解真空硫磺细菌亚群中基于硝酸盐的硫化物呼吸与基于氧气的硫化物呼吸的相对重要性。调查者将调查Beggiatoa spp的垂直分布和丰度。并确定液泡硝酸盐如何影响固氮，并将衍生和使用重要的氮循环基因(nifD、nifH和NRFA同系物)的探针。除了培养研究生，该项目还将通过与加州大学戴维斯分校生物学本科生计划的互动，专门针对弱势和代表性不足的本科生。

Large, vacuolate, nitrate-accumulating bacteria such as Beggiatoa can oxidize a majority of the sulfide produced in a variety of marine niches. Closely related sulfur bacteria (vacuolated attached filaments or VAF) that do not accumulate nitrate are abundant on surfaces at marine sulfidic vents. Collectively, these phylogenetically coherent organisms are the only Proteobacteria known to contain vacuoles and it is clear that they play a significant role in the nitrogen and sulfur cycles of a variety of marine environments. Beggiatoa species are also members of the bacterial consortium known as "black band disease" that constitutes a widespread and lethal disease of corals. The principal investigator has isolated a stable culture of a 7-micron diameter vacuolate Beggiatoa from black band disease (strain BBD) that accumulates nitrate and seems to be capable of dinitrogen fixation. This cultured strain and a number of natural populations of VAF and nitrate-accumulating Beggiatoa are the focus of this project. The investigator will use microelectrode and molecular analyses to understand the relative importance of nitrate- vs. oxygen-based respiration of sulfide in subgroups of vacuolate sulfur bacteria. The investigator will survey the vertical distribution and abundance of vacuolate Beggiatoa spp. and determine how vacuolar nitrate affects nitrogen fixation, and will derive and use probes of important nitrogen cycle genes (nifD, nifH and a nrfA homologue). In addition to training a graduate student, the project will specifically target disadvantaged and underrepresented undergraduates through interaction with the Biology Undergraduate Scholars Program at UC-Davis.