Effects of Filtered Lake Water on Colony Formation and Growth Rate in Microcystis aeruginosa of Different Physiological Phases

Abstract

ABSTRACT Lake water, which contained an abundance of zooplankton, was passed through a 0.15 μm membrane filter, and 20 ml were immediately added to 80 ml suspensions of Microcystis aeruginosa in either exponential or late stationary growth phase. In the control system, 20 ml of BG-11 medium were added. After two days, colony formation was observed in the treatment of the exponential growth phase M. aeruginosa, whereas no colonies were formed in the control. The mean number of cells per unit of M. aeruginosa increased significantly compared with that in the control (P<0.05). However, late stationary phase M. aeruginosa populations, both in the control and in the treatment, were strongly dominated by unicells and paired cells, and no colonies were formed. As a consequence, no significant difference in the mean number of cells per unit was detected between the control and the treatment (P≫0.05). However, no significant difference in the growth rate was detected between the control and the treatment (P>0.05), regardless of growth phase. These results indicated that any chemicals released from zooplankton had no influence on the growth of M. aeruginosa, and the inducible colony formation in M. aeruginosa was related to physiological phase.