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

波罗的海的特点是其明显的水平和垂直盐度梯度，其独特之处在于其62%的表面区域为半咸水。已知高等底栖和远洋生物的分布模式与盐度有关，微咸条件下的多样性最低。在微生物的第一次分析中，基于细菌16S rRNA基因的焦磷酸测序，我们能够表明细菌群落也经历了不同的系统发育水平沿着盐度梯度的明显变化。此外，有证据表明，一个适应的微咸水细菌群落，代表的Verrucomicrobia的系统发育成员。该项目旨在测试浮游细菌群落组成从海洋向半咸水和湖沼条件的转变如何影响浮游碳循环中细菌介导的功能。这将通过两种不同的方法进行研究：（1）在不同盐度的站点进行的船上实验调查中，除了原核生物多样性外，我们还将评估微生物的功能，包括与有机碳处理有关的广泛到高度特异性的细菌活动，以及（2）盐度对中部表层浮游细菌的组成和功能的直接影响，波罗的海将通过实验性地操纵盐度水平来研究。在这里，作为一个额外的功能因素，除了底物利用，我们也将研究原核生物对捕食和原核生物和噬菌体之间的营养相互作用的反应。

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.