DNA virus-host patterns in lake and marine environments over the last glacial cycle

Viruses are crucial to population control, biogeochemical cycling, and host evolution, making them essential for ecosystem function. Here, we explore long-term virus-host interactions in lake and marine environments across the late Pleistocene and Holocene. We analysed sedimentary ancient DNA (sedaDNA) from five Siberian lakes and four Subarctic/Antarctic marine cores to infer past DNA virus taxa from metagenomic sequences. Viruses accounted for 0.089% (357 161 reads) of mapped reads across 2084 taxa. Virus communities differ between lakes and marine sites, with lakes dominated by Caudoviricetes and marine environments featuring Caudoviricetes and Algavirales. Each time series shows compositional changes in virus communities from the Pleistocene to the Holocene, supporting the inference that sedaDNA can reconstruct time-resolved ancient viral assemblages. Among the most abundant viruses, we identified 83 virus-host pairs known from published literature to infect bacterial, archaeal, or eukaryotic hosts, and assessed their associations using co-variation patterns. Over millennia, virus-host co-variations are particularly stable in marine systems, especially for phytoplankton-infecting viruses. However, in the Bering Sea, we find a lack of virus-host correlation, likely because an Arctic Pelagibacter strain expanded rapidly after the Bering Strait opened, potentially due to absent viral infection. Antagonistic patterns also appear between bacteriophages and hosts, possibly linked to shifts between lytic and lysogenic cycles in response to environmental changes. This study shows that sedaDNA can reveal ancient viral community structures and long-term ecological patterns, highlighting the value of ancient viromes in understanding ecosystem- specific responses to environmental change.