Abstract: A kind of enriched culture medium was prepared according to Formula BG-11 out of filtered natural pearl-culturing water. A strain of freshwater bacterium, Exiguobacterium sp.013 (E. sp.013), which was found to be able to promote growth of freshwater cyanophyte Microcystis ichthyoblab in the axenic culture condition, was purified and cultured, and then used in a 24hr incubation experiment inoculated simultaneously with four species of freshwater cyanophytes (Microcystis aeruginosa, Microcystis flosaqua, Merismopedia.sp，and Microcystis wesenbergii) according to a set bacterium/cyanophyte ratio in density.Specific growth rates and cell densities of the cyanophytes were observed to determine effect of E. sp.013 on their growth and variation of population of the dominant consortium in the culture media. Results show that E. sp.013 significantly promoted growth of M. aeruginosa, M. flos-aquae and M. wesenbergii and extended their stable growing periods. E. sp.013 did not have much promoting effect on growth of Merismopedia.sp, but did significantly extend its stable growing period. During the culturing period, E. sp.013 was found to account for 46% or more of the total population of the bacteria and cyanophytes in the solution and maintain an absolute dominancy, indicating that E. sp.013 is capable of regulating the cyanophytes.

Key words: cyanophytes, growth-promoting bacterial strain, Exigubacterium, algal bloom