By means of impact filtration we have immobilized Ostreococcus sp. cells containing viral particles, from water samples taken at the proximities of the mouth of the Patagonian Chubut River (43.346578S, 65.016628W; 43.339828S, 65.012608W and 43.340038S, 65.024728W). Viral DNA content from the immobilized virus / host complexes were purified and analyzed by standard molecular methods. Phylogenetic analysis of new Ostreococcus virus (OV) sequences from the Patagonian Coast, Argentina and homologous sequences from public databases was performed.
Our findings indicate that viruses obtained from immobilized Ostreococcus sp. cells are virtually identical to those obtained from virus cultivated in-vitroand viruses present in a concentrate obtained by tangential filtration. In comparison with traditional methods, the co-immobilization on solid phase by filtration impact is less laborious, it does not imply the use of complex equipments and it is more economical. Furthermore, the method has the potential to generate data about the hosts infected with viruses identified, which is not possible by other independent virological methods of cultivation.
The results from the phylogenetic analysis showed that the Patagonian sequences correspond to a divergent viral clade, even more the rest of OV sequences that were analyzed clustered into six additional phylogenetic groups. Analyses of the 18S rDNA libraries confirmed that the Patagonian sequences corresponded to an Ostreococcus sp., supporting also, a close relationship with other Clade A strains, described elsewhere. The presence of a clade A strain in Patagonia corroborates previous results indicating that clade A strains are ubiquitous. Although many viral sequences from remote locations were highly related to each other, we found that some of phylogenetic groupings were associated to particular geographic locations. These results suggest a role for allopatric cladogenesis in the viral diversification of this viral group. On the other hand, and in agreement with previous observations, other viral lineages included sequences with diverse geographic origins. Overall, jointly with analyses of ancestral trait trajectories performed here, indicated that this environmental viral group presents an evolutionary dynamics in which geographical isolation has a role in OV diversification but can be followed by rapid dispersion to remote places.