To study the effect of attached bacteria on the carbon metabolism of M. aeruginosa, the percentage of carbonic anhydrase(CA) produced bacteria in total attached bacteria was analyzed. The result showed that the ratio of CA produced bacteria is 11.6% in a typical cyanobacterial bloom from Lake Taihu. An attached bacterium strain P201, which produced large amount of extracellular carbonic anhydrase, was isolated from M. aeruginosa assemblage. It was identified as a strain of Pseudomonas fluorescence by its ITS molecular characteristic. Effects of P201 on the growth of M. aeruginosa in different HCO₃^- concentrations were investigated. The results showed that no matter in the higher or the lower HCO₃^- culture medium, P201 could promote the growth of M. aeruginosa, which suggested that CA produced attached bacteria could enhance the growth of M. aeruginosa by regulating the ambient carbon environment.