Microbial diversity and function within the salinity gradient of the Baltic Sea

波罗的海以其独特的水平和垂直盐度梯度为特征，其独特的特征是其62%的表面区域为微咸条件。众所周知，在半咸淡环境下，与盐度相关的分布模式和多样性最小值适用于高级底栖生物和远洋生物。在对微生物的首次分析中，基于细菌16S rRNA基因的焦磷酸测序，我们能够显示细菌群落沿着盐度梯度在不同的系统发育水平上经历了明显的变化。此外，有证据表明有一个适应的微咸水细菌群落，以Verrucomicrobia的一个系统发育成员为代表。本项目旨在测试浮游细菌群落组成从海洋到咸淡水和湖泊条件的转变如何影响细菌在远洋碳循环中的介导功能。这将通过两种不同的方法进行调查：(1)在不同盐度站点的船上实验调查中，我们将评估除原核生物多样性外，微生物功能涵盖与有机碳处理相关的广泛到高度特定的细菌活动；(2)盐度对中部咸淡波罗的海表面浮游细菌的组成和功能的直接影响将通过实验操纵盐度水平进行检查。在这里，除了底物利用之外，我们还将研究原核生物对捕食的反应以及原核生物与细菌捕食者之间的营养相互作用。

The Baltic Sea is characterized by its distinct horizontal and vertical salinity gradients, with the unique feature that 62% of its surface zone is represented by brackish conditions. Salinity-related distribution patterns and a diversity minimum at brackish conditions are known for higher benthic and pelagic organisms. In a first analysis for microorganisms, based on pyrosequencing of bacterial 16S rRNA genes, we were able to show that also bacterial communities experience distinct shifts at different phylogenetic levels along the salinity gradient. Moreover, there is evidence for an adapted brackish water bacterial community, represented by a phylogenetic member of the Verrucomicrobia. This project aims to test how the shift in bacterioplankton community composition from marine to brackish and limnic conditions affects bacterially mediated functions within the pelagic carbon cycle. This will be investigated by two different approaches: (1) in ship-board experimental investigations at stations of different salinity we will assess, besides prokaryotic diversity, microbial functionality covering broad to highly specific bacterial activities related to organic carbon processing, and (2) the direct impact of salinity on the composition and function of surface bacterioplankton in the central, brackish Baltic Sea will be examined by experimentally manipulating salinity levels. Here, as an additional functional factor besides substrate utilization, we will investigate also prokaryotic response towards predation and trophic interactions between prokaryotes and bacterivores.