Effects of the cultivable bacteria attached to Microcystis colonies on the colony size and growth of Microcystis

The interactions between bacteria and algae may play a significant part in the formation and development of algal blooms. The bloom-forming cyanobacterium Microcystis occurs mainly as colonial form in natural waters, and thus it is necessary to study the interaction between bacteria and colonial Microcystis. This paper aimed to investigate effects of the cultivable bacteria attached to Microcystis colonies on the colony size and growth of colonial Microcystis aeruginosa. Eleven bacterial strains were isolated from M. aeruginosa colonies collected from Lake Taihu. Among these bacteria, seven bacterial isolates significantly influenced the colony size of M. aeruginosa, and four bacterial isolates significantly influenced the growth rate of M. aeruginosa. Four isolates, related to the Exiguobacterium, Delftia, Bacillus and Stenotrophomonas, significantly decreased the colony size of M. aeruginosa by 36-51%, and two isolates, assigned to the Chryseobacterium and Pseudomonas chengduensis, significantly increased the M. aeruginosa colony size by 89% and 63%, respectively, while these isolates had no effect on the cyanobacterial growth rate. Two isolates, belonged to the Rheinheimera and Pseudomonas, significantly decreased the growth rate of M. aeruginosa by 47% and 36%, respectively, and one bacterial strain related to Aeromonas increased the cyanobacterial growth rate by 22%, while these isolates had no effect on the cyanobacterial colony size. One isolate belonged to Sphingomonas was found to significantly increase the colony size of M. aeruginosa by 80% and significantly decrease the growth rate of M. aeruginosa by 21%. PCR-denaturing gradient gel electrophoresis (PCR-DGGE) analysis showed that all of the bacterial isolates were able to colonize M. aeruginosa colonies. Our data suggested that the bacteria attached to Microcystis colonies might influence the cyanobacterial colony size and growth, and thus influence the formation and development of Microcystis blooms.