Distribution and activity of virioplankton in the Toliara Large Reef (Madagascar)

Abstract

Until then, the study of aquatic viruses concerned almost exclusively temperate and polar environments while the tropics were rarely explored. In this study, we examined the spatial and temporal variability of viral and bacterial communities in two different tide periods (spring/ neap tide), on 22 stations covering the Toliara Large Reef (TLR) located in Madagascar. The coupling of these two communities was also analyzed in several contrasted stations of the reef by physiological and ecological descriptors means. The epifluorescence microscopy technique allowed to achieve the bacterial and viral count support of this work. The results obtained show that the bacterial and viral concentrations for the whole TLR were significantly higher during spring than neap tide, probably because of the hydrodynamics very marked in this area. In addition, the Mitomycin C used permitted to establish that the cells fraction in phase of lysogenic infection was very low (< 3%) despite the oligotrophic status of TLR waters. This suggests that the lysogeny was the viral reproduction dominant strategy, which was diverted spontaneously and in a continuous way towards the lytic pathway, under the solar conditions’ influence. Finally, we show that the viruses form a dynamic and ubiquitous component of reef ecosystems, whose activity appears once again, closely related to the physico-chemical and biological environment nature.

Keywords: Virus, lysogeny, lysis, tropical latitude