Rhythms of lysis: viral regulation of prokaryotic turnover across diel cycles

Diel rhythms structure microbial activity in the ocean, yet the role of
viral lysis in driving short-term community dynamics remains poorly
understood. Here, we combined dilution experiments, high-resolution
microbiome sampling, and extracellular ribosome sequencing to investigate
diel virus–host interactions in the South China Sea. Viral lysis accounted
for an average of 41% of Synechococcus and 24% of heterotrophic bacterial
mortality at night. Overall, 74% of amplicon sequence variants (ASVs)
showed lysis signals, with many displaying significant diel fluctuations.
Notably, rare taxa comprised a large fraction of diel-responsive ASVs,
indicating high turnover among low-abundance populations. Synechococcales
exhibited tightly coupled nighttime peaks in abundance and lysis, while
SAR11 and Flavobacteriales showed delayed lysis after late-day growth. In
addition, virus-mediated mortality had a stronger influence on
metabolically active and diel-responsive ASVs. These findings highlight
viral lysis as a temporally structured and taxon-specific force sustaining
microbial turnover and diversity in oligotrophic waters.