Who are the ubiquitous, biomass-significant red fluorescent picoplanktonic cells in temperate and polar surface oceans?

该提案的目的是识别包含额外红色荧光的大型浮游细菌群的细胞，并确定它们的代谢潜力。我们提出验证一个假设，即这些红色荧光细胞是含细菌叶绿素的有氧无氧光养浮游细菌（AAPs）。先前的研究表明，AAPs缺乏自养无机碳同化途径，不能进行光自养，其大部分细胞能量依赖异养。然而，我们对红色荧光细胞的3h -亮氨酸和35s -蛋氨酸摄取的临时测量表明，这些细胞对这两种氨基酸的摄取率虽然高于光合蓝藻聚球菌的摄取率，但明显低于平均异养浮游细菌细胞的氨基酸摄取率。因此，红色荧光细胞可能会收集光来光化学氧化有机分子，以维持它们在光温带和极地海洋中无处不在的庞大种群。该项目建议(i)采用流式细胞术从大型浮游细菌的额外红色荧光组中分选系统发育相关细胞；（ii）设计和测试特定的寡核苷酸探针，以鉴定流动分选细胞；检测流动分选细胞中细菌叶绿素基因的存在；（iii）检查红色荧光组系统发育组成的纬度变化。为了实现上述目标，我们将把重点放在对首次观察到这些微生物的大西洋收集的样品进行分子分析上。我们的最终目标是解释它们在海洋生态系统中的生态作用。

The aim of the proposal is to identify the cells comprising the extra red fluorescence group of large bacterioplankton and to ascertain their metabolic potential. We propose to test a hypothesis that these red fluorescent cells are aerobic anoxygenic phototrophic bacterioplankton (AAPs) containing bacteriochlorophylls. Previous studies show that AAPs lack autotrophic inorganic carbon assimilation pathways and are incapable of photoautotrophy, relying on heterotrophy for the majority of their cellular energetics. However, our provisional measurements of 3H-leucine and 35S-methionine uptake by the red fluorescent cells suggested that the uptake rates of both amino acids by these cells, although being higher than the uptake rates by Synechococcus phototrophic cyanobacteria, are considerably lower than the amino acid uptake rates by mean heterotrophic bacterioplankton cells. Therefore, the red fluorescent cells probably harvest light to photochemically oxidise organic molecules in order to sustain their sizeable ubiquitous population in the photic temperate and polar ocean. The project proposes (i) to phylogenetically affiliate cells, flow cytometrically sorted from the extra red fluorescence group of large bacterioplankton; (ii) to design and test specific oligonucleotide probes for identification of flow sorted cells; to examine the presence of bacteriochlorophyll genes in flow sorted cells; (iii) to examine latitudinal variations in phylogenetic composition of the red fluorescence group. In order to meet the above objectives we will focus on molecular analysis of samples collected in the Atlantic Ocean, where these microorganisms were first observed. Our ultimate goal is to explain their ecological role in oceanic ecosystems.