Preliminary Study Of The Competition Mechanism Between Microcystis Aeruginosa And Microcystis Flos-aquae

Microcystis is a kind of dominant populations of water-blooming alage in freshwater lakes. Although many researchs have been carried out to disclose the outbreak and maintenance reasons of microcystis, the mechanims of Microcystis, especially Microcystis aeruginosa, to be the dominant species in the freshwater is not entirely clear yet. In order to reveal the dominant formation mechanism of M. aeruginosa, we studied on the interspecific competition between the M. aeruginosa FACHB905and M.flos-aquae FACHB-1028by co-cultivation and GC-MS analysis methods. Results mainly include:①M. aeruginosa and M. flos-aquae:M. aeruginosa exhibited mutual competitve inhibition, and the former showed stronger inhibition against the latter, which was enhanced along with the culture time. Twenty-four days after inoculation, the cell numbers of M. aeruginosa were reduced by about20-30%, while that of M. flos-aquae were reduced by about89%.②The initial ratio of cell densities had significant influence on the mutual competitive inhibition between M. aeruginosa and M. flos-aquae, while temperature and Nutrients had little effect on it. When the cell density of M. aeruginosa was greater than M. flos-aquae, M. aeruginosa showed great inhibition against the growth of M. flos-aquae, however, when the cell density of M. aeruginosa was less than M. flos-aquae, the inhibition between the two alage was similar. Temperature had little effect on the competition between M. aeruginosa and M. flos-aquae’s competition, but the competitive inhibition between the two species was decreased.③The competitive inhibition between M. aeruginosa and M. flos-aquae was related with the metabolites of M. aeruginosa. When M. flos-aquae was grew in the mediums containing metabolites of M. aeruginosa and co-cultured algae, the growth of M. flos-aquae was inhibited seriously. However, the metabolites of M. flos-aquae and co-cultured algae did not show significant effect on M. aeruginosa growth.④Forty-four compounds had been observed by GC-MS analysis of the metabolites collected from the uni-and co-cultured conditions. Among these compounds, D-Limonene, Butylated Hydroxytoluene, Dodecane,2-methyl-Dichloroacetic acid,4-hexadecyl ester, Heptacosane,1-chloro-3-Chloropropionic acid and octadecyl ester appeared only in metabolites of M. aeruginosa; the compounds such as1,1’-Biphenyl,2,2’,5,5’-tetramethyl, Trichloroacetic acid, hexadecyl ester, E-15-Heptadecenal,1-Octadecanol and1-Hexacosanol appeared only in the co-cultured medium; the compounds such as1-Heptadecene, Bromoacetic acid, hexadecyl ester and Hexacosane appeared only in metabolites of M. flos-aquae. Furthermore, The HPLC analysis indicated no microcystin was detected, which implied that the competitive inhibition of M. aeruginosa on M. flos-aquae has nothing to do with the production of microcystin.Based on the studies, we speculate that allelopathic metabolites M. aeruginosa might play an important role in the dominant formation or maitainance of M. aeruginosa in Lake Taihu, which could help us to understand the mechanism of microcystis bloom formation and and outbreak in Lake Taihu.