Fonseca, A.; Middelboe, M.; Holmfeldt, K.; Bell, E.; Humborg, C.; Norkko, A.; Nascimento, F. J. A.

Viruses regulate microbial mortality and biogeochemical cycling in marine sediments; however, the ecological drivers of sediment viral communities remain unclear. Infauna, including sediment-dwelling meiofauna and macrofauna, are major ecosystem engineers that reshape sediment structures and microbial processes, but their influence on viruses is unknown. We combined infaunal gradient incubations with metagenomic and metatranscriptomic analyses to assess viral DNA and RNA responses. DNA viruses showed increased abundance (3-fold), diversity, richness, and transcriptional activity under higher infauna abundance conditions, whereas RNA viruses remained unaffected, revealing striking selectivity. This selectivity reflects an infauna-dependent component mediated by bacterial activity that cannot be explained by host abundance alone. Infection profiling revealed increased transcription of viral replication and structural genes, and lytic viruses under high infauna conditions. These findings establish infauna as a previously overlooked regulator of DNA virus dynamics, integrating viral ecology into faunal-microbial frameworks in benthic ecosystems and suggesting potential influences on geochemical cycles.