Diatom viruses are an important driver of diatom cell lysis and the associated release of
various organic compounds into the environment. By infecting host cells, viruses
indirectly influence the composition and dynamics of microbial communities that inhibit
the vicinity of diatoms or are directly associated with them. These interactions remain
poorly understood, despite their potential importance for understanding carbon cycling
in marine ecosystems and their role in ecological processes such as phytoplankton
blooms. In this study we investigated how the diatom-infecting virus PnGalRNAV type
II affects cultures of Pseudo-nitzschia galaxiae and the associated microbial
community, including free-living and particle-associated microorganisms in the
phycosphere and detritosphere. We also examined how the dynamics of these microbial
fractions change during viral infection. Our results showed that viral infection
accelerates the demise of the diatom population and alters microbial community
structure by increasing microbial abundance, particularly within the free-living fraction.
Using a Fluorescence in situ hybridization protocol combined with epifluorescent
microscopy, we observed shifts in the dynamics of Alphaproteobacteria,
Gammaproteobacteria and Bacteroidota, with Bacteroidota becoming the dominant
group across all three fractions, likely due to their ability to degrade complex
polysaccharides. Our findings demonstrate that infection by PnGalRNAV type II affects
not only P. galaxiae itself but also indirectly reshapes the composition and dynamics of
the associated microbial community. Consequently, viral infection of this diatom may
have an important part in the cycling of the organic matter and carbon in marine
ecosystems.
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