Differing assemblage composition and dynamics in T4-like myophages of two neighbouring sub-alpine lakes
Résumé
1. Bacteriophages play an important role in plankton population dynamics and biogeochemical cycling, but their community dynamics and diversity are still poorly known, especially in fresh waters. 2. We conducted a 1-year investigation of the T4-like bacteriophages in the surface waters of two Western European peri-alpine lakes (lakes Annecy and Bourget), using fingerprinting and cloning-sequencing approaches targeting the major capsid protein g23 gene. 3. Our results suggest that T4-like bacteriophages are diverse (we found several new sequences) and differed substantially between the two lakes. Further, these phages displayed seasonal patterns with marked shifts in community composition. 4. Examining the dynamics of some individual constituents (e. g. DGGE bands), we found that (i) the majority of these myoviruses were rare (mean relative abundance <1%) and only a few were abundant (mean relative abundance >5%); (ii) the dominance of the most abundant DGGE bands changed throughout the year and their dynamics were very different between the two lakes; (iii) only a few bands (e. g. <20%) were detectable throughout the year and their proportion was higher in the oligomesotrophic Lake Bourget. 5. Our results suggest a highly dynamic T4-like myoviral assemblage. T4-like-viruses seem to conform to a standard model of community organisation and a common type of species abundance curve, with mainly rare organisms that occasionally may become abundant (termed a 'seed bank' for virus assemblages).