The addition of native viruses to the three different types of water consistently stimulated VP, the increase being significant in all except one case (i.e. with hypersaline water) (Fig. 1). In the lacustrine, marine and hypersaline

water, VP increased, respectively, by 53.4 ± 11.1%, 37.2 ± 8.7% and 20.3 ± 3.4% as compared with the control (Fig. 2a, d and g). Similar NVP-LDE225 order observations have been reported previously when the probability of the contact rate between viruses and their prokaryotic hosts is artificially accentuated by viral enrichment (Noble et al., 1999; Schwalbach et al., 2004; Bonilla-Findji et al., 2008). These results suggest that a larger number of susceptible hosts were infected, thus promoting viral proliferation. Such lytic ‘success’ indicates that the protocol for generating viral neoconcentrates did not alter viral integrity and infectivity considerably. In contrast, in all the cross-transplant experiments involving allochtonous (non-native) viruses, no additional

VP was observed (Fig. 2b, c, e, f, h and i). At most, VP increased by 5.3 ± 1.2% in the incubation with marine viruses and hypersaline prokaryotes (Fig. 2h). The main finding here is that the mixing of viruses and prokaryotes from water of different osmolarity does not always result in a lytic success as was observed by Sano et al. (2004) and Bonilla-Findji et al. (2009). However, in this study, planktonic viruses were tested for their ability to move between ecosystems as learn more click here well as, to a larger extent, their capacity to move between domains of life. In the hypersaline lake Retba, the prokaryotic community has been shown to harbor up to 50% of Archaea (Y. Bettarel, T. Bouvier, C. Bouvier et al., unpublished data; Sime-Ngando et al., 2010), together

with a viral cortege dominated by pleomorphic archeoviruses including lemon-shaped, spindle, filamentous and spherical-shaped viruses (Sime-Ngando et al., 2010). Although it has been hypothesized that some particular viruses can span all domains of life, such as some of the thermophilic archaeal viruses (Rice et al., 2004), we know that most of viruses typically do not pass the genus barrier (Ackermann & Dubow, 1987). Archaeal viruses form a particular assemblage that is fundamentally different in morphotype and genome from the DNA viruses of the other two domains of life: the Bacteria and Eukarya (Pranghishvili et al., 2006). Transmission electron microscopy observations of Retba virioplankton also revealed extremely low proportions (about 1% of the total) of VLPs that morphologically resembled head-and-tail viruses (Sime-Ngando et al., 2010).

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