Abstract:
In recent years, remarkable progress has been made in the field of virus environmental
ecology. In marine ecosystems for example, viruses are now thought to play pivotal roles in
the biogeochemical cycling of nutrients and to be mediators of microbial evolution through
horizontal gene transfer. In soils, the diversity and ecology of viruses is poorly understood,
but evidence supports the view that these differ substantially from aquatic systems. Desert
biomes cover ~33% of global land masses, yet the diversity and roles of viruses in these
dominant ecosystems remain poorly understood. There is evidence that hot hyperarid desert
soils are characterised by high levels of bacterial lysogens and low extracellular virus counts.
In contrast, cold desert soils contain high extracellular virus titres. We suggest that the
prevalence of microbial biofilms in hyperarid soils, combined with extreme thermal regimes,
constitute strong selection pressures on both temperate and virulent viruses. Many desert soil
virus sequences show low identity values to virus genomes in public databases, suggesting
the existence of distinct and as yet uncharacterised soil phylogenetic lineages (e.g.
cyanophages). We strongly advocate for amplification-free metavirome analyses while
encouraging the classical isolation of phages from dominant and culturable microbial isolates
in order to populate sequence databases. This review provides an overview of recent
advances in the study of viruses in hyperarid soils, the factors that contribute to viral abundance and diversity in hot and cold deserts and suggests technical recommendations for
future studies.
