Impact of salinity changes on viral production during the paleoenvironmental history of Baltic Sea sediments

波罗的海深层地下沉积物代表了这个大陆内盆地的古环境档案，该盆地在过去经历了湖泊、咸淡水和海洋环境的变化。IODP Exp. 347的目的是研究这些环境变化对底栖微生物群落的影响。由于病毒控制微生物种群，并通过感染细胞的裂解介导碳周转，它们对微生物和生物地球化学过程产生重大影响。在第一个资助期，我们已经开始分析病毒和它们的宿主细菌，它们是深层生物圈中数量众多且活跃的组成部分。为了快速准确地计数培养基中的病毒，我们已经开发了一种流式细胞术方案，现在可以用于大量样品，这将适用于沉积物中的病毒计数。从我们的培养实验中，我们获得了36株分离株；其中一些将被有效地描述为新种甚至属。生理分析显示，它们在耐盐性方面存在相当大的差异。在分离物中发现了不同的病毒，这些病毒要么是由抗生素丝裂霉素诱导的，要么是在细菌生长过程中大量产生的。在该项目中，我们将建立一个噬菌体基因组数据库，这可能会揭示深层生物圈中持久性的重要病毒特征，并减轻对深层生物圈中特定噬菌体的识别，例如宏基因组或单细胞基因组。此外，我们目前对渗透冲击作为病毒产生诱导剂的研究将从纯培养扩展到环境样品。分析细胞裂解过程中的微生物群落结构和有机碳组成，以及随后机会性细菌对细胞物质的摄取，将有助于了解病毒在波罗的海古环境史中的作用。

Deep subsurface sediments of the Baltic Sea represent a paleoenvironmental archive of this intra-continental basin which has undergone alterations between limnic, brackish and marine conditions in the past. The aim of IODP Exp. 347 has been to investigate the impact of these environmental changes on benthic microbial communities. As viruses control microbial populations and mediate carbon turnover due to lysis of infected cells, they have a major impact on microbial and biogeochemical processes. In the first funding period, we have started to analyze viruses and their host bacteria as numerous and active components of the deep biosphere. For fast and accurate counting of viruses in culture media, we have developed a protocol for flow cytometry that can now be used for a large number of samples which will be adapted for counting viruses in sediments. From our cultivation experiments, we have obtained 36 isolates; some of them will be validly described as new species or even genera. Physiological analysis revealed considerable differences in their salinity tolerance. Different viruses have been identified in the isolates, which are either induced by the antibiotic mitomycin or produced at high numbers during growth of the bacteria. In the proposed project, we will establish a database of phage genomes from our isolates which will possibly reveal viral features important for the persistence in the deep biosphere and alleviate the identification of specific phages in e.g. metagenomes or single-cell genomes from the deep biosphere. Furthermore, our current studies on osmotic shock as an inducer for virus production will be extended from pure cultures to environmental samples. Analyzing microbial community structures and organic carbon composition during cell lysis and subsequent uptake of cell material by opportunistic bacteria will help to understand the role of viruses during the paleoenvironmental history of the Baltic Sea.