Seasonal patterns in Arctic prasinophytes and inferred ecology of Bathycoccus unveiled in an Arctic winter metagenome

Prasinophytes occur in all oceans but rarely dominate phytoplankton populations. In contrast, a single ecotype of the prasinophyte Micromonas is frequently the most abundant photosynthetic taxon reported in the Arctic from summer through autumn. However, seasonal dynamics of prasinophytes outside of...

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Bibliographic Details
Published in:The ISME Journal
Main Authors: Joli, Nathalie, Monier, Adam, Logares, Ramiro, Lovejoy, Connie
Format: Text
Language:English
Published: Nature Publishing Group 2017
Subjects:
Original Article
Arctic
Amundsen Gulf
Beaufort Sea
Phytoplankton
Online Access:http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5437359/
http://www.ncbi.nlm.nih.gov/pubmed/28267153
https://doi.org/10.1038/ismej.2017.7
Description
Summary:Prasinophytes occur in all oceans but rarely dominate phytoplankton populations. In contrast, a single ecotype of the prasinophyte Micromonas is frequently the most abundant photosynthetic taxon reported in the Arctic from summer through autumn. However, seasonal dynamics of prasinophytes outside of this period are little known. To address this, we analyzed high-throughput V4 18S rRNA amplicon data collected from November to July in the Amundsen Gulf Region, Beaufort Sea, Arctic. Surprisingly during polar sunset in November and December, we found a high proportion of reads from both DNA and RNA belonging to another prasinophyte, Bathycoccus. We then analyzed a metagenome from a December sample and the resulting Bathycoccus metagenome assembled genome (MAG) covered ~90% of the Bathycoccus Ban7 reference genome. In contrast, only ~20% of a reference Micromonas genome was found in the metagenome. Our phylogenetic analysis of marker genes placed the Arctic Bathycoccus in the B1 coastal clade. In addition, substitution rates of 129 coding DNA sequences were ~1.6% divergent between the Arctic MAG and coastal Chilean upwelling MAGs and 17.3% between it and a South East Atlantic open ocean MAG in the B2 Clade. The metagenomic analysis also revealed a winter viral community highly skewed toward viruses targeting Micromonas, with a much lower diversity of viruses targeting Bathycoccus. Overall a combination of Micromonas being relatively less able to maintain activity under dark winter conditions and viral suppression of Micromonas may have contributed to the success of Bathycoccus in the Amundsen Gulf during winter.

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