Molecular Analyses of the Population Dynamics and Activity of a Newly Identified Bacterioplankton Group: The SAR11 Cluster

在过去的十年中，浮游细菌对浮游生物系统的生物量和生物地球化学活动的显著贡献已经变得很明显。直到最近，在确定构成这些群落的微生物种类方面进展缓慢，因为大多数存在的微生物（直接计数）不能在培养中恢复。近年来引入的分子技术为研究未培养微生物物种的种群动态提供了手段。该项目基于分子数据，证明了一种新的微生物类群SAR11的存在，并表明该类群约占马尾藻海非蓝藻微生物活动的20%。SAR11集群是通过克隆天然马尾藻浮游细菌种群的16S核糖体DNA遗传标记检测到的亲缘类群。这项研究将通过在马尾藻海的BATS站提供这些生物分布的时间序列和深度剖面信息来扩展早期的观察。利用SAR11簇（SAR11R）和海洋聚球菌（SYNF）的特异性DNA探针，以及真细菌、真核生物和通用小亚基核糖体rna的通用探针，将测量马尾藻海浮游细菌群落的季节性变化动态。该项目的具体目标是：1)验证SAR11群集种群在夏季分层期间达到数值最大值的假设；2)验证了SAR11集群广泛分布于少营养海洋区域高营养区的假设；3)验证SAR11簇分布与有氧光异养活性相关的假设；4)提供其他浮游细菌群分布的平行时间序列信息，这些信息是由接近完成的进一步遗传研究揭示的。细菌光异养是开放海洋中一个活跃过程的理论可能对通过微生物环的碳通量的计算产生巨大影响。“异养”浮游细菌的现有产量太大，无法用标准的0.6呼吸转换因子来解释初级生产力估计，但可以更好地解释与光异养相关的更高的生长效率。

Within the past decade it has become evident that bacterioplankton contribute significantly to biomass and biogeochemical activity in planktonic systems. Until recently progress in identifying the microbial species which constitute these communities was slow because the majority of the organisms present (direct counts) could not be recovered in culture. Recently introduced molecular techniques are providing the means to study the population dynamics of uncultivated microbial species. This project is based on molecular data which demonstrates the existence of a novel microbial group, the SAR11 cluster, and indicates that this group accounts for about 20% of the non- cyanobacterial microbial activity in the Sargasso Sea. The SAR11 cluster is a related group of species which were detected by cloning 16S ribosomal DNA genetic markers from a natural Sargasso Sea bacterioplankton population. This research will extend earlier observations by providing time-series and depth profile information on the distribution of these organisms at the BATS station in the Sargasso Sea, where they were first observed. The dynamics of seasonal changes in the Sargasso Sea bacterioplankton community will be measured using specific DNA probes for the SAR11 cluster (SAR11R) and marine Synechococcus (SYNF), as well as general probes for eubacterial, eukaryotic and universal small subunit ribosomal RNAs. The specific goals of the project are: 1) to test the hypothesis that the SAR11 cluster population reaches a numerical maximum during summer stratification; 2) to test the hypothesis that the SAR11 cluster is distributed widely in the upper euphotic zone ofoligotrophic oceanic regions; 3) to test the hypothesis that the distribution of the SAR11 cluster is correlated with aerobic photoheterotrophic activity; 4) to provide parallel time series information on the distribution of other planktonic bacterial groups which are being revealed by further genetic studies nearing completion. The theory that bacterial photoheterotrophy is an active process in the open ocean can potentially have a dramatic influence on calculations of carbon flux through the microbial loop. The standing crop of "heterotrophic" bacterioplankton is too large to be explained form primary productivity estimates using a standard 0.6 respiratory conversion factor, but could be better explained using the higher growth efficiencies associated with photoheterotrophy.