AME 58:249-259 (2010)  -  DOI: https://doi.org/10.3354/ame01381

Seasonal variation in viral-induced mortality of bacterioplankton in the water column of a large mesotrophic lake (Lake Biwa, Japan)

A. S. Pradeep Ram1,4, Y. Nishimura1,5, Y. Tomaru2, K. Nagasaki2, T. Nagata1,3,*

1Centre for Ecological Research, Kyoto University, 2-509-3 Hirano, Otsu, Shiga 520-113, Japan
2Harmful Algal Bloom Division, National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima 739-0452, Japan
3Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan
4Present address: Laboratoire ‘Microorganismes: Génome et Environnement’, Université Blaise Pascal, Clermont-Ferrand II, UMR CNRS 6023, 63177 Aubiére Cedex, France
5Present address: Port and Airport Research Institute, 3-1-1 Nagase, Yokosuka, Kanagawa, 239-0826, Japan
*Corresponding author. Email:

ABSTRACT: Viruses are ubiquitous and abundant in aquatic systems, yet knowledge of virus–bacteria interactions in thermally stratified water columns of large lakes is limited. We explored the possible factors that affect viral abundance, infection rate, and the relative importance of viral lysis to heterotrophic nanoflagellate (HNF) grazing as a mortality factor of bacterioplankton in the upper (euphotic zone, 5 m) and deeper (aphotic zone, 50 m) layers of the large mesotrophic Lake Biwa, Japan. Data obtained for a full seasonal cycle indicated that bacterial abundance was the best predictor (r2 = 0.85) of viral abundance (range 1.0 × 1010 to 4.1 × 1010 viruses l–1), yielding an average virus:bacteria ratio of 8.2 ± 1.3 (SD). Variation in the frequency of visibly infected cells (range 1.8 to 4.1%) was largely accounted for by the linear combination of bacterial production and HNF abundance (r2 = 0.81, p < 0.001, n = 24). The percentage of daily bacterial production destroyed by viruses was estimated to be high (52.7 ± 16.2%) in the upper layer during the stratification period, which was on average 3.0-fold greater than the percentage of bacterial production consumed by HNF in that layer. In contrast, the corresponding value in the deeper layer was moderate (13.6 ± 5.2%), being 0.6-fold lower than the percentage of bacterial production consumed by HNF. Our data suggest that carbon and nutrient flux patterns controlled by viruses and HNF vary with depth in thermally stratified water columns of Lake Biwa.


KEY WORDS: Viruses · Bacteria · Frequency of infected cells · Burst size · Seasonal dynamics · Stratified large lake


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Cite this article as: Pradeep Ram AS, Nishimura Y, Tomaru Y, Nagasaki K, Nagata T (2010) Seasonal variation in viral-induced mortality of bacterioplankton in the water column of a large mesotrophic lake (Lake Biwa, Japan). Aquat Microb Ecol 58:249-259. https://doi.org/10.3354/ame01381

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