Original paper

Viral abundance and its related factors in a stratified lake

Honjo, Mie; Matsui, Kazuaki; Ishii, Nobuyoshi; Nakanishi, Masami; Kawabata, Zen'ichiro


We investigated the vertical distribution and dynamics of viral abundance in the euphotic epilimnion and aphotic hypolimnion during periods of stratification in Lake Biwa, Japan. The abundance of virus-like particles (VLPs) was lower and more constant in the hypolimnion than in the epilimnion. Simple correlation analysis demonstrated that during periods of stratification, VLP abundance in the hypolimnion was positively correlated with chlorophyll-a concentration, the bacterial abundance of the >0.8-μm fraction, and water temperature. On the other hand, VLP abundance in the epilimnion was also positively correlated with chlorophyll-a concentration and the bacterial abundance of the >0.8-μm fraction, but was negatively correlated with the bacterial abundance of the 0.2-0.8-μm fraction and was not correlated with water temperature. We observed no correlation between VLP abundance and total bacterial abundance in either the epilimnion or the hypolimnion. Multiple regression analysis indicated that VLP abundance was explained by chlorophyll-a concentration in both the epilimnion and the hypolimnion. Aphotic environment and abundance of phytoplankton and bacteria in the hypolimnion, suggesting that main host of viruses is bacteria rather than phytoplankton. However our results suggest that VLP abundance in the hypolimnion related to the other factors as well as bacterial abundance.


bacterial abundancechlorophyll-awater temperatureepilimnionhypolimnionlake biwa