Exploring the virioneuston: Viral-bacterial interactions between ocean and atmosphere (VIBOCAT)

海洋表面微层（SML）是海洋和大气之间小于1毫米的薄边界层，是海洋领域中尚未得到充分研究的组成部分。与底层水体相比，该生境中病毒的频繁富集，从淡水研究推断出的形成不同群落的趋势，以及它们在颗粒和海洋喷雾气溶胶上的出现，使我们可以得出这样的结论，即SML中的病毒可能在调节海气交换过程中发挥重要作用。我假设来自SML的噬菌体，属于所谓的vivioneuston，可以通过频繁的宿主细胞裂解（诱导病毒分流=细胞裂解导致的碳释放）影响生物地球化学碳循环，并从空气-海洋界面启动微生物循环，这与人们普遍认为微生物循环过程始于上层水柱的观点形成了对比。我试图通过使用最先进的组学，可视化和培养方法，提供对噬菌体在SML中的作用的见解。该项目的目的是研究SML中噬菌体（溶性或溶原性）的主要感染机制，从而判断它们诱导病毒分流的潜力。为此目的，将从波罗的海收集SML样本，并用于提取和至少三个噬菌体-宿主系统的基因组测序（首次用于海洋SML）和测序宏基因组（首次用于野外SML）。宏基因组的样本将从一个非常平静的海面收集，一个光滑的海面，通常富含有机物质，并与非光滑的SML和下面的水进行比较。通过尺寸分级过滤，颗粒或非颗粒相关的病毒-细菌群落将被调查，这意味着它们通过下沉颗粒到远洋区对微生物环的贡献。在病毒基因组和宏基因组的帮助下，我将研究基因组整合前噬菌体的存在，为SML的溶原性感染提供证据。此外，这些数据将用于研究宿主对抗病毒的防御系统（称为集群规则间隔短回文重复=CRISPR），揭示宿主对病毒压力的适应性，并帮助噬菌体与宿主连接（通过CRISPR-间隔器-病毒原间隔器匹配）。本提案未发表的初步数据中给出了SML细菌菌株携带前噬菌体和CRISPR系统的第一个证据。利用宏基因组数据，我将阐明病毒辅助代谢基因在感染过程中对宿主细胞代谢调节的重要性。培养实验和透射电镜分析将分别用于评估sml提取的噬菌体的裂解行为和形态。总之，VIBOCAT项目将有助于我们了解海洋-大气边界层中细菌-病毒的相互作用，并揭示病毒群对海洋微生物环和碳循环的可能影响。

Viruses in the sea-surface microlayer (SML), a <1 mm thin boundary layer between ocean and atmosphere, are highly understudied components in the marine realm. Frequent enrichment of viruses in this habitat compared to the underlying water, the tendency to form distinct communities as deduced from a freshwater study, and their appearance on particles and sea-spray aerosols allow to conclude that viruses in the SML could have an important role in the regulation of air-sea exchange processes. I hypothesize that bacteriophages from the SML, belonging to the so-called virioneuston, can affect biogeochemical carbon cycling by frequent host cell lysis (induction of the viral shunt=carbon release due to cell lysis) and jump-start the microbial loop from the air-sea interface in contrast to the common belief that processes of the microbial loop begin in the upper water column. I seek to provide insights into the role of bacteriophages in the SML by using state-of-the-art -omics, visualization, and cultivation methods. The objectives of the project are to study the prevailing infection mechanism of phages in the SML (lytic or lysogenic) and thus to judge their potential to induce the viral shunt. For this purpose, SML samples will be collected from the Baltic Sea and used for extraction and genome sequencing of at least three bacteriophage-host systems (first time for a marine SML) and for sequencing metagenomes (first time for a field SML). Samples for metagenomes will be collected from a very calm sea surface, a slick, usually enriched in organic material and compared to non-slick SML and the underlying water. By size-fractionated filtration, particle or non-particle associated viral-bacterial communities will be investigated implying their contribution to the microbial loop via sinking particles to the pelagic zone. With the help of the viral genomes and metagenomes, I will investigate the existence of genome-integrated prophages, providing evidence for lysogenic infections in the SML. Moreover, these data will be used to study defense systems (known as clustered regularly interspaced short palindromic repeat=CRISPR) of the host against viruses, revealing host adaptations to viral pressure and aid to link phages to their hosts (via CRISPR-spacer-viral protospacer matches). First evidence of a SML bacterial strain harboring prophages and a CRISPR system is given in the unpublished preliminary data of this proposal. Using the metagenomic data, I will elucidate the importance of viral auxiliary metabolic genes for modulation of host cell metabolism during infection. Cultivation experiments and transmission electron microscopy analysis will be used to estimate lytic behavior and morphology of SML-extracted phages, respectively. In summary, the project VIBOCAT will benefit our understanding of bacterial-viral interactions in the ocean-atmosphere boundary layer and reveal likely impacts of the virioneuston on microbial loop and carbon cycling in the ocean.