Original paper

Do small grazers influence virus-induced mortality of bacteria in Lake Bourget (France)?

Jacquet, Sté phan; Domaizon, Isabelle; Personnic, Sé bastien; Sime-Ngando, Té lesphore


We performed simple tests to assess the importance of the presence or absence of small flagellated predators on the stimulation of viral-induced bacterial mortality (VIBM) in Lake Bourget (France) during three periods of the year (March-April, May and August 2003). To achieve this goal, samples were filtered either through < 5 or < 1.2 μm filters in order to keep or eliminate the smallest predators. We found that the VIBM was always enhanced in the presence of the predators after only 24 h. The viral impact was multiplied by about 8-fold at the end of March, 2.5-fold in May and 7-fold in August in the < 5 μm compared to the < 1.2 μm treatment. A clear and positive relationship was found between flagellates concentrations and the VIBM (r = 0.99, n = 3, p< 0.05). Our results highlight a tight coupling between the different compartments of the aquatic microbial loop, and more especially what could be a synergistic cooperation between grazing- and virus-induced mortality of bacteria.


virusesprotistsbacteriabacterial mortalitylake