To do so, we collected 111 deep-sea sediment samples and applied and compared three different approaches based on virus counts during time-course experiments. We conducted a study over a large spatial scale to investigate virus decomposition rates in benthic deep-sea ecosystems. Although the impact of viral infections on the functioning of benthic deep-sea ecosystems has been recognized recently ( 13), the extent to which virus decomposition influences the functioning and biogeochemical processes of the deep-sea floor is completely unknown. Indeed, virus decomposition provides labile organic compounds (i.e., proteins and nucleic acids) and the associated key elements (N, P) ( 21) and represents an important process for sustaining microbial food webs, especially in highly oligotrophic ecosystems, such as the deep-sea floor, that are characterized by very low inputs of organic material ( 22). Virus decomposition can have important consequences on both the composition of viral assemblages and the flow of energy and nutrients in aquatic ecosystems ( 2, 20). The information presently available suggests that sunlight, UV radiation, temperature, salinity, and different extracellular organic compounds (such as proteases and nucleases) can promote virus decomposition in oceanic waters ( 14– 19). These findings have provided clues to explain why benthic deep-sea ecosystems can sustain relatively high prokaryotic biomass and turnover despite their food limitations ( 7, 11, 12).Īfter cell lysis, the viruses released can either infect other hosts or undergo decay and/or decomposition ( 2, 3). Previous studies carried out in deep-sea sediments worldwide have shown that nearly all the prokaryotic C production is transformed into organic detritus by viral lysis, thus representing an additional important trophic resource for the metabolism of noninfected microbes ( 13). The inputs of organic matter that reach the ocean floor sustain the metabolism of benthic food webs, which are largely dominated by prokaryotic biomass ( 11, 12).
Except for hydrothermal vents and cold seeps, where chemoautotrophic production represents the main engine that sustains the ecosystem functioning, life in deep-sea ecosystems is dependent on the input of organic matter produced by photosynthesis in the surface waters of the oceans ( 9, 10).
They thus provide essential “goods and services” for the entire biosphere ( 7, 8). 65% of the earth’s surface and have key roles in biomass production and biogeochemical cycles ( 6, 7). Our data indicate that the decomposition of viruses provides an important, previously ignored contribution to deep-sea ecosystem functioning and has an important role in nutrient cycling within the largest ecosystem of the biosphere.ĭeep-sea ecosystems cover ca. Organic material released from decomposed viruses is equivalent to 3 ± 1%, 6 ± 2%, and 12 ± 3% of the input of photosynthetically produced C, N, and P supplied through particles sinking to bathyal/abyssal sediments. We estimate that on a global scale the decomposition of benthic viruses releases ∼37–50 megatons of C per year and thus represents an important source of labile organic compounds in deep-sea ecosystems. Virus decomposition rates in deep-sea sediments are high even at abyssal depths and are controlled primarily by the extracellular enzymatic activities that hydrolyze the proteins of the viral capsids. Here, using various independent approaches, we show that in deep-sea sediments an important fraction of viruses, once they are released by cell lysis, undergo fast decomposition. However, the extent to which the decomposition of viral particles (i.e., organic material of viral origin) influences the functioning of benthic deep-sea ecosystems remains completely unknown. Viruses are key biological agents of prokaryotic mortality in the world oceans, particularly in deep-sea ecosystems where nearly all of the prokaryotic C production is transformed into organic detritus.
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