Diverse microorganisms adapted to life at high salt concentrations are found in globally distributed hypersaline environments that comprise ~50% of continental waters. The abundance of prokaryotes increases with salinity, reaching values even higher than 108 cells per milliliter at salinities above 25%. These microbial communities are frequently dominated by members of the domain Archaea (both haloarchaea from the Euryachaeaota and nanohaloarchaea from the DPANN superphylum) along with Bacteria predominantly from the Salinibacter genus. These systems are also characterized by the presence of viral-like particles (VLP) that can reach up to 1010 VLP/ml (11), more than three orders of magnitude higher than estimates from surface marine communities. Measured ratios of viruses to microbes increase with salinity (from seawater to highly salt-saturated ponds) with values between 10 and 100 VLPs per cell, and can even reach 300 VLPs per cell. Hypersaline environments at close-to-saturation salinities are typically inhospitable to bacterivorous organisms found in other aquatic habitats, including protists and heterotrophic nanoflagellates. Unusually high viral abundances and virus-to-cell ratios along with reduced bacterivory in hypersaline environments suggest that viral infections and the subsequent modulation of microbial cell fate have a significant role in shaping prokaryotic population dynamics.

In this talk, we will be presenting an overview of how the combination of cultivation and culture independent techniques (single cell genomics, microarrays, dissolved DNA, viral and cellular metagenomics) has allowed the assignment of virus to three of the main prokaryotic groups in close to saturation systems, namely, Haloquadratum, the nanohaloarchaea and the extremely halophilic bacterium Salinibacter ruber. Then, we will show how temporal tracking of cultures and natural and manipulated salter crystallizer ponds unveils the tempo and modo of evolution of viral assemblages and can also be used to explore the relationship between intra and extracellular virus abundance and activity.

Solar salters have been proposed as model systems to study the units of bacterial diversity that matter for ecosystem functioning. They are also a tractable yet privileged scenario for the study of virus-host interactions within an ecological context.