High level of intergenera gene exchange shapes the evolution of haloarchaea in an isolated Antarctic lake

Significance Horizontal gene exchange across species boundaries is considered infrequent relative to vertical inheritance that maintains species coherence. However, haloarchaea living in hypersaline environments take a more relaxed approach to gene exchange. Here we demonstrate that in Deep Lake, Antarctica, haloarchaea exchange DNA between distinct genera, not just species, with some of the DNA being long (up to 35 kb) and virtually 100% conserved. With extremely low cell division rates in the cold (e.g., six generations per year), the remarkable extent of lateral exchange could conceivably homogenize the population. It is therefore equally notable that despite the demonstrated capacity for exchange, different genera are maintained, their coexistence being linked to genomic differences conferring ecotype distinctions that enable niche adaptation.