Genome-resolved biogeography reveals multidimensional structuring of freshwater giant viruses across global deep lakes

Giant viruses (GV) have emerged as significant ecosystem regulators, yet the global distribution patterns of these individual species and the biogeographic processes driving these patterns remain largely unknown. To address this knowledge gap, researchers reconstructed metagenome-assembled genomes (MAGs) of GV from 35 deep freshwater lakes spread across five continents.

The analysis revealed a diverse array of 1663 non-redundant MAGs, with approximately 84% of these MAGs not previously associated with a known species, significantly broadening our understanding of freshwater GV diversity.

These MAGs were categorized into two main groups: cosmopolitan species, which exhibit a global distribution across multiple viral lineages, and geographically restricted lineages that are confined to specific regions. The cosmopolitan species, identified to include families of Imitervirales, Pimascovirales, and Styxvirales order mirusviruses, are characterized by larger genomes and expanded gene repertoires involved in host interactions.

These traits may enhance their ability to engage with a variety of hosts, thereby contributing to their widespread presence across the globe.

Interestingly, the geographical distribution of these GV species appears to be influenced by their vertical partitioning within the lake's water column. MAGs were predominantly found in either the epilimnion (upper layer) or hypolimnion (lower layer), with a clear preference for one layer over the other. This vertical segregation was observed consistently across different lakes, indicating a conserved pattern possibly linked to the water column's thermal stratification.

This finding suggests that physical connectivity between ecosystems may play a crucial role in the dispersal and distribution of GV, as it would limit horizontal movement across different lake environments. Overall, the study underscores the complex interplay of horizontal dispersal limitations, vertical partitioning, and lineage-specific evolutionary histories in shaping the biogeography of giant viruses in deep freshwater lakes.