Diversity and ecology of viruses in hyperarid desert soils

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.