Occurrence of Blue-green Algae and Algal Lytic Bacteria in Lake Biwa

Abstract

Seasonal changes of the number of blue-green algae-lysing microbes have been studied in relation to that of bloom-forming blue-green algae at two stations in Southern Lake Biwa in 1985. The numbers of the lyric microbes in surface water were in a range from 102 to 106PFUs/ml at Yabase station and from 102 to 104PFUs/ml at Shimosakamoto station. The numbers of those in the surface layer of sediment at Yabase and Shimosakamoto stations were in a range from 103 to 106PFUs/g wet wt and from 103 to 105PFUs/g wet wt, respectively. At both stations, especially at Yabase station, the number of the lytic microbes correlated with chlorophyll a. concentration and with the cell number of Anabaena solitaria.Because bacteria always occupied the majority in the algae-lysing microbes, 8 strains of lytic bacteria were isolated. These 8 strains and the strain of LB-1 isolated from the water at Shimosakamoto station in 1984 were identified as gliding bacteria. All of them indicated strong lytic activities against 5 strains belonging to family Nostocaceae including A. solitaria and one strain of Phormidium tenue belonging to family Oscillatoriaceae, but they were hardly or not able to lyse other blue-green algae, green algae, and bacteria tested.These results suggest that the bloom of A. solitaria in Lake Biwa should be affected by lyric bacteria.