Abstract
Little is known about viruses in oxygen-deficient water columns (ODWCs). In surface ocean waters, viruses are known to act as gene vectors among susceptible hosts. Some of these genes may have metabolic functions and are thus termed auxiliary metabolic genes (AMGs). AMGs introduced to new hosts by viruses can enhance viral replication and/or potentially affect biogeochemical cycles by modulating key microbial pathways. Here we identify 748 viral populations that cluster into 94 genera along a vertical geochemical gradient in the Cariaco Basin, a permanently stratified and euxinic ocean basin. The viral communities in this ODWC appear to be relatively novel as 80 of these viral genera contained no reference viral sequences, likely due to the isolation and unique features of this system. We identify viral elements that encode AMGs implicated in distinctive processes, such as sulfur cycling, acetate fermentation, signal transduction, [Fe–S] formation, and N-glycosylation. These AMG-encoding viruses include two putative Mu-like viruses, and viral-like regions that may constitute degraded prophages that have been modified by transposable elements. Our results provide an insight into the ecological and biogeochemical impact of viruses oxygen-depleted and euxinic habitats.
Highlights
1234567890();,: 1234567890();,: IntroductionViral infections can exert controls on species composition and activities of microorganisms [3] and can indirectly influence microbial metabolic fluxes, energy homeostasis, and metabolic reprogramming of the host cells [4]
These authors contributed : Paraskevi Mara, Dean Vik
From all six samples we sequenced a total of 1.5 M reads, 2 orders of magnitude more sequencing depth than previously derived from any other oxygen-deficient water columns (ODWCs) viromes [22] and ~70% of sample sequencing depth for recent surface ocean viromes [11, 47]
Summary
Viral infections can exert controls on species composition and activities of microorganisms [3] and can indirectly influence microbial metabolic fluxes, energy homeostasis, and metabolic reprogramming of the host cells [4]. Virus-encoded AMGs are known to include genes involved with most of central carbon metabolism [7], nitrogen [8], phosphorus [9] and sulfur cycling [10, 11], nucleotide metabolism [12,13,14], oxidative stress responses [15] and methane oxidation [16]. We explore the diversity of viruses detected in Cariaco Basin, as well as the variety of genetic elements detected within viral metagenomes prepared from water samples collected through the water column (ranging from fully oxygenated to euxinic) that may play roles in shaping prokaryotic metabolic activities
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