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

细菌-叶绿素A(BCHL A)是一种光合色素，以前被认为是缺氧光异养细菌唯一的分子生物标志物。尽管生活在含氧水中的产氧光异养细菌早在20年前就被发现，但Bchl a被认为只在产氧细菌光合作用期间表达，因此被诊断为产氧细菌光合作用。这些细菌需要缺氧条件来合成它们的细菌-叶绿素，并且在光存在的情况下，使用水以外的分子(如硫化物、硫化物、氢、铁等)作为光合作用的电子供体。这与蓝藻和真核生物的生存方式形成了鲜明的对比，它们的主要色素，叶绿素a(或其密切的衍生物)，使水成为光合作用的电子供体，顺便形成分子氧作为废物。最近检测Bchl a的生物物理方法表明，好氧细菌光合作用可能在世界表层海洋中更为普遍，而且也不仅限于生态位(缺氧微区)环境。除了限制Bchl a作为缺氧环境古生态生物标志物的使用(本研究的主题)外，证实全球表层海洋中存在显著浓度的Bchl a意味着由于好氧产氧光营养生物的显著生物量和光合能通量。这可能对碳固定和海洋碳运输有重要的影响，但对于解释好氧厌氧光营养细菌与非光营养细菌的海洋生态，特别是在贫营养水域中，肯定是重要的。为了系统地确认BChL a信号在含氧海水中的重要性，这项研究将在几个地点的水样中进行：i)严格的化学鉴定色素bChla及其相关形式，ii)调查其存在的相关颗粒大小关系(指示微区缺氧)III)对其在可能的目标微生物(例如，红杆菌)培养物中的存在进行初步的微生物学研究)调查bChla在水柱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.