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

• Applicant: Dr. Janina Rahlff
• Subject Area: Microbial Ecology and Applied Microbiology
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 446702140

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.

• DFG Programme: WBP Fellowship
• International Connection: Sweden
• Host: Privatdozentin Karin Holmfeldt, Ph.D.