Elucidating Viral Communities During a Phytoplankton Bloom on the West Antarctic Peninsula.

Tomás Alarcón-Schumacher,Josefa Antón,Sergio Guajardo-Leiva,Beatriz Díez

doi:10.3389/fmicb.2019.01014

Abstract

In Antarctic coastal waters where nutrient limitations are low, viruses are expected to play a major role in the regulation of bloom events. Despite this, research in viral identification and dynamics is scarce, with limited information available for the Southern Ocean (SO). This study presents an integrative-omics approach, comparing variation in the viral and microbial active communities on two contrasting sample conditions from a diatom-dominated phytoplankton bloom occurring in Chile Bay in the West Antarctic Peninsula (WAP) in the summer of 2014. The known viral community, initially dominated by Myoviridae family (∼82% of the total assigned reads), changed to become dominated by Phycodnaviridae (∼90%), while viral activity was predominantly driven by dsDNA members of the Phycodnaviridae (∼50%) and diatom infecting ssRNA viruses (∼38%), becoming more significant as chlorophyll a increased. A genomic and phylogenetic characterization allowed the identification of a new viral lineage within the Myoviridae family. This new lineage of viruses infects Pseudoalteromonas and was dominant in the phage community. In addition, a new Phycodnavirus (PaV) was described, which is predicted to infect Phaeocystis antarctica, the main blooming haptophyte in the SO. This work was able to identify the changes in the main viral players during a bloom development and suggests that the changes observed in the virioplankton could be used as a model to understand the development and decay of blooms that occur throughout the WAP.

Highlights

The Southern Ocean (SO) is one of the world’s most productive marine regions
The Prymnesiovirus PaV related sequences, that form part of the extended Mimivirus group, are identified to be the most abundant community members. These results suggest that the structure and composition of the viral community in Chile Bay vary throughout the austral summer, can change from a bacterial-viruses dominated community to a eukaryotic-viruses dominated one, during periods of high productivity
Novel genomes belonging to the most abundant viruses were recovered, while genomic analyses revealed a new genus within the Myoviridae group, and the first virus (Phycodnavirus) described that can infect P. antarctica, an important primary producer in the Antarctic marine food webs

Summary

Introduction

The Southern Ocean (SO) is one of the world’s most productive marine regions. It plays a key role in carbon drawdown and contributes to an estimated 20% of global oceanic CO2 uptake (Takahashi et al, 2002). Seasonality in the SO leads to environmental variations; such as increased light availability and sea ice cover retreat along the summer, inputting metals and other nutrients to the surface waters and promoting water column stratification The latter leads to large phytoplankton blooms (Vernet et al, 2008; Giovannoni and Vergin, 2012; Mendes et al, 2012), resulting in increased carbon uptake in coastal waters (Bunse and Pinhassi, 2017). The West Antarctic Peninsula (WAP) blooms are acknowledged to be dominated first by large diatoms (>10 μm), followed by smaller flagellates such as haptophytes and cryptophytes (Ducklow et al, 2012; Schofield et al, 2017) These groups modulate carbon sinking, microbial community composition, strongly influence higher trophic levels and support food webs (Arrigo, 1999; Piquet et al, 2011)

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Discussion

Conclusion