Single-Stranded DNA Viruses in Antarctic Cryoconite Holes

Abstract

Antarctic cryoconite holes, or small melt-holes in the surfaces of glaciers, create habitable oases for isolated microbial communities with tightly linked microbial population structures. Viruses may influence the dynamics of polar microbial communities, but the viromes of the Antarctic cryoconite holes have yet to be characterized. We characterize single-stranded DNA (ssDNA) viruses from three cryoconite holes in the Taylor Valley, Antarctica, using metagenomics. Half of the assembled metagenomes cluster with those in the viral family Microviridae (n = 7), and the rest with unclassified circular replication associated protein (Rep)-encoding single-stranded (CRESS) DNA viruses (n = 7). An additional 18 virus-like circular molecules encoding either a Rep, a capsid protein gene, or other unidentified but viral-like open reading frames were identified. The samples from which the genomes were identified show a strong gradient in microbial diversity and abundances, and the number of viral genomes detected in each sample mirror that gradient. Additionally, one of the CRESS genomes assembled here shares ~90% genome-wide pairwise identity with a virus identified from a freshwater pond on the McMurdo Ice Shelf (Antarctica). Otherwise, the similarity of these viruses to those previously identified is relatively low. Together, these patterns are consistent with the presence of a unique regional virome present in fresh water host populations of the McMurdo Dry Valley region.

Taxonomy of prokaryotic viruses: 2018-2019 update from the ICTV Bacterial and Archaeal Viruses Subcommittee

“…The case is well illustrated by the families Microviridae and Leviviridae, which have received relatively little attention from the ICTV (i.e., two subfamilies, six genera and 21 species versus two genera and four species, respectively). Environmental studies have indicated that the family Microviridae contains at least five unclassified subfamilies [40][41][42][43][44][45][46][47]. Recently, Callanan et al [48] predicted 331 species and 247 genera among the single-stranded RNA phages, potentially leading to a significant expansion of the family Leviviridae.…”

Flexible genes establish widespread bacteriophage pan-genomes in cryoconite hole ecosystems

“…Cryoconite holes possess abundant and active virus communities, with circa 10 8 virus-like particles (VLP) g −1 of sediment and new virus production rates in the order of 10 7 VLP g −1 h −1 33 . A broad range of novel viruses have been described in these habitats 34 , 35 . Across Earth’s glaciated regions, cryoconite holes typically experience near-freezing temperatures, nutrient limitation and possess a highly truncated food web 36 .…”

Cryoconite Hole Location in East-Antarctic Untersee Oasis Shapes Physical and Biological Diversity

“…CHs are currently perceived as microbial hotspots (Edwards et al, 2013;Weisleitner et al, 2019a) because their biodiversity and productivity are much higher than in other supraglacial zones (Anesio et al, 2009;Cook et al, 2016). The presence of viruses, bacteria, micro-algae, fungi, protozoa, and sometimes metazoans indicate that CHs are simple trophic systems (Mueller et al, 2001;Mueller and Pollard, 2004;Porazinska et al, 2004;Hodson et al, 2008;Sommers et al, 2019). Primary producers such as cyanobacteria fix inorganic carbon via photosynthesis and provide nutrients for the heterotrophic fraction of the community (Mueller et al, 2001;Morgan-Kiss et al, 2006;Bagshaw et al, 2016).…”