BacterioChlorophyll A in the Open Ocean - Do We Need to Reassess its Role as a Biomarker?

细菌叶绿素A（bChla）是一种光合色素，以前被认为是缺氧光合异养细菌的独特分子生物标志物。虽然生活在好氧沃茨中的缺氧光合异养细菌是在20年前发现的，但bChl a被认为仅在缺氧细菌光合作用期间表达，因此是缺氧细菌光合作用的诊断。这些细菌需要缺氧条件来合成它们的细菌叶绿素，并且在光的存在下，使用除水以外的分子（例如硫化物、硫化合物、氢、Fe等）作为光合电子供体。这与蓝细菌和真核生物的存在模式形成对比，蓝细菌和真核生物的主要色素叶绿素a（或其密切衍生物之一）使水能够充当光合作用的电子供体，顺便形成分子氧作为废物。 最近的生物物理方法，检测bChl a表明，有氧细菌光合作用可能是更普遍的在世界的海洋表面，也不限于生态位（缺氧微带）的环境。以及限制使用bChl a作为缺氧环境的古生态生物标志物（本研究的一个主题），确认在全球表层海洋中存在显著浓度的bChl a意味着一个显着的生物量和光合能通量，由于有氧缺氧光养生物。这可能会或可能不会有重要的影响，碳固定和海洋碳运输，但肯定是重要的，在解释海洋生态的好氧无氧光合细菌与非光合细菌，特别是在贫营养沃茨。为了系统地确认bChl a信号在含氧海水中的重要性，本研究将在几个地点的水样中进行：i）严格化学鉴定色素bChla及其相关形式，ii）研究其出现的相关粒度关系iii）对其在可能的目标微生物中的发生进行初步微生物学研究（如蔷薇枝）培养研究了bChla在水体和沉积环境中的生物地球化学转化。

ABSTRACTOCE-0118045Bacteriochlorophyll A (bChl a) is a photosynthetic pigment which has been formerly considered a unique molecular biomarker for the anoxic photoheterotrophic bacteria. Although anoxygenic photoheterotrophic bacteria which live in oxic waters were discovered some 20 years ago, bChl a was considered to be expressed solely during, and thus diagnostic of, anoxygenic bacterial photosynthesis. These bacteria require anoxic conditions to synthesize their bacteriochlorophylls and, in the presence of light, use molecules other than water (e.g. sulfide, sulfur compounds, hydrogen, Fe etc) as photosynthetic electron donors. This is to be contrasted to the mode of existence of cynanobacteria and eukaryotes whose primary pigment, chlorophyll a (or one of its close derivatives), enables water to serve as the electron donor for photosynthesis, incidentally forming molecular oxygen as a waste product. Recent biophysical methods that detect bChl a have suggested that aerobic bacterial photosynthesis may be much more prevalent in the world's surface ocean, and also not limited to niche (anoxic microzonal) environments. As well as limiting the use of bChl a as a paleoecological biomarker for anoxic environments (a subject of this study), confirmation of the presence of a significant concentration of bChl a in the global surface ocean implies a significant biomass and photosynthetic energy flux due to aerobic anoxygenic phototrophs. This may or may not have important implications to carbon fixation and ocean carbon transport, but certainly is important in explaining the marine ecology of aerobic anoxygenic phototrophs in relation to non-phototrophic bacteria, especially in oligotrophic waters. In order to systematically confirm the importance of the bChl a signal in oxic seawater, this study will, in water samples from several sites: i) rigorously chemically identify the pigment, bChla, and its related forms, ii) investigate associated particle size relationships of its occurrence (indicative of microzonal anoxia) iii) conduct preliminary microbiological studies of its occurrence in likely target microbial (e.g Roseobacter clade) culturesiv) investigate the biogeochemical transformation of bChla in water columns and sedimentary environments.