Virus‐induced spore formation as a defense mechanism in marine diatoms

Abstract

Algal viruses are important contributors to carbon cycling, recycling nutrients and organic material through host lysis. Although viral infection has been described as a primary mechanism of phytoplankton mortality, little is known about host defense responses. We show that viral infection of the bloom-forming, planktonic diatom Chaetoceros socialis induces the mass formation of resting spores, a heavily silicified life cycle stage associated with carbon export due to rapid sinking. Although viral RNA was detected within spores, mature virions were not observed. 'Infected' spores were capable of germinating, but did not propagate or transmit infectious viruses. These results demonstrate that diatom spore formation is an effective defense strategy against viral-mediated mortality. They provide a possible mechanistic link between viral infection, bloom termination, and mass carbon export events and highlight an unappreciated role of viruses in regulating diatom life cycle transitions and ecological success.

Deep particle stocks following the summer bloom around the Kerguelen islands: Insights into diatoms physiological state, community structure and mortality modes

“…These observations are congruent with previous reports of increased dominance of Chaetoceros Hylaochaete resting spores (CRS) in trap samples (Rembauville et al, 2016) and of dominance of CRS together with E. antarctica in sediments over the Kerguelen plateau (Armand et al, 2008b). New findings also show that viral infection of the bloom-forming genus Chaetoceros could induce mass formation of resting spores as a defense strategy (Pelusi et al, 2020), which is yet another mecanism that could lead to mass carbon export events by diatom spores.…”

Trade-off between sex and growth in diatoms: Molecular mechanisms and demographic implications

“…The heterogeneous capacity to proceed to meiosis can be attributed to physiological, genetic, and/or epigenetic differences in the cell population. One example of this heterogeneity in diatom cell populations is the formation of resting stages, which are produced only by a subset of the population ( 29 , 30 ). Heterogeneity has also been demonstrated by studies of gene expression ( 31 ) and chloroplast redox state measurements on individual diatom cells ( 32 ).…”

Controls on the Silicon Isotope Composition of Diatoms in the Peruvian Upwelling

“…So far, the δ 30 Si signal in resting spores has not been investigated in detail. There are many uncertainties, including the 1) exact formation mechanism of resting spore, which can form under nutrient depletion or viral attack (Oku and Kamatani, 1997;Pelusi et al, 2020) and 2) the question if the fractionation factor is comparable to vegetative cell formation.…”