However, more studies are needed to support this statement. Among the cross-inoculation experiments, only the production of marine prokaryotes was stimulated by the supplementation of allochtonous viruses. The IE in PHP averaged 198.1 ± 20.9% and 292.4 ± 42.2% with freshwater and hypersaline viruses, respectively PLX4032 purchase (Fig. 2m and n). In this coastal marine station, the addition of presumably
uninfectious viruses (as demonstrated above, Fig. 2e and f) might have been of nutritional benefit for the native prokaryotes in this environment. Auguet et al. (2008) have shown that the amendment of heat-inactivated viruses from the Charente Estuary (France) also resulted in a significant stimulation of bacterial heterotrophic production. Z-VAD-FMK nmr We know that free viruses cannot survive for extended periods (Wilhelm et al., 1998) and that most
viruses are inactive in water (Suttle & Chen, 1992). Then, a substantial fraction of the transplanted planktonic viruses, under the degradative effects of ambient proteases, UV radiation and temperature (Bettarel et al., 2009), could have also entered the available DOM pool. Although dissolved free and combined amino acids represent the majority of the total virus-mediated release of organic carbon, we now know that viruses themselves can contribute to the DOM pool available for prokaryotes. Indeed, viral particles have been reported to constitute up to 6% of the released organic carbon (Middelboe & Jørgensen, 2006). However, such estimates have been Paclitaxel nmr addressed only on rare occasions and thus more studies are needed to elucidate the direct
nutritional role of viruses for prokaryotic cells. Clearly, we cannot rule out that some bioavailable, nonviral DOM was added to the incubations in the neoconcentrate. However, the final concentration factor of this size fraction was only three- to fourfold, as determined from the VPR in the incubations. Furthermore, the lack a of uniform response in PHP in the treatments also supports the hypothesis that the DOM in the neoconcentrate was a minor source of bioavailable carbon (e.g. Fig. 2k, n and p). For example, it is probable that DOC concentrations were the highest in the hypersaline environment, and yet we only observed an increase in PHP in the marine station with the hypersaline viral addition and not in the two other sites. It is therefore probable that another mechanism, such as the supply of highly bioavailable organic carbon of viral origin, is also stimulating PHP. Finally, we suggest that the addition of a large number of probably uninfectious (freshwater and hypersaline) viruses might have been responsible for the sharp increase in the production of marine prokaryotes. Interestingly, we already know that viruses are of nutritional value for protists (Gonzàlez & Suttle, 1993; Bettarel et al.