Research Of Inducing Microcystis Aeruginosa Colony

In recent years, harmful algal bloom induced by lake eutrophication has become one of the worst ecological disaster to the fresh water ecosystems, especially in China. Algal bloom can reduce the water quality, inhibit the growth of other aquatic organisms, destroy the ecological water landscape and ecological environment, and even do harm to human health. To prevent and control algal blooms, it is necessary to have a clear understanding about the mechanism of algal bloom.Microcystis aeruginosa is one of the dominant species in the algal bloom, due to its specific morphological structure and physiological function. M. aeruginosa has two different existence forms, single cell and colony. Generally, M. aeruginosa exist in the form of colony in natural lakes, so that it can effectively resist the predation. The colony form also plays a significant role in the algal bloom. However, in the laboratory, M. aeruginosa exist in the form of single cell, even the cell density at a very high level, it is one obstacle to the research of the algal bloom mechanism.In this series of experiments, we chose M. aeruginosa912as research object. By various of experiments, we got a clear understanding about the growth characteristics of M. aeruginosa, found a mature and stable process to induce the M. aeruginosa colony and got lots of informations about the M. aeruginosa morphological structure. The results showed that:1). The optimum light intensity and temperature for culture the M. aeruginosa912in the laboratory were50001x and28℃, in this condition the cell density could reach the maximum as106.8×106cell/ml. In a complete growth period, temperature was the decisive role in determining the length of the adjustment phase. M. aeruginosa had the longest and shortest adjustment phase in the condition of30℃and25℃. respectively.2). M. aeruginosa912formed big colonies under the predation pressure of the Ochrmonas sp., as some of the colony contained more than2000single cells (estimates). There were three stages during mixed culture of the M. aeruginosa912and Ochrmonas sp.. For the first predation period, a large proportion of M. aeruginosa912was eaten by Ochrmonas sp. and its cell density was rapidly decreased. In the second gradual change period, the cell density of the two species remained stable, in the end of this period small colonies appeared. The third one was rebirth period, the number and the size of the colony were firstly growing, then the colony began to break up, finally the single cell took the most part of the sample. Ochrmonas sp. grazed on M. aeruginosa912severely, as80%of the M. aeruginosa912was consumed within the first10days, so Ochrmonas sp. can be used as the "bane" of M. aeruginosa912to control the algal bloom.3). The colonies induced by the predation of Ochrmonas sp. had smaller intercellular space than the natural ones. Single cells in the colony had thicker gelatinous sheath than the normal cells.4). In single cells pure cultivation model, the cell polysaccharide of per unit biomass was kept stable. When the colony was forming, the cell polysaccharide of per unit biomass increased. The colony cells grew relatively slowly. When the colonies were cultured separately, a number of colonies were forming in the first stage, the cell polysaccharide of per unit biomass increased. In the second stage, colonies broke up gradually, single cells entered into a rapid growth period, the cell polysaccharide of per unit biomass dropped significantly.