Comparison of community composition between Microcystis colony-attached and free-living bacteria, and among bacteria attached with Microcystis colonies of various sizes in culture

Abstract

A better understanding of the distribution pattern of bacterial community in the Microcystis phycosphere will aid in elucidating the role of bacteria in the formation of cyanobacterial bloom. In the present study, we aimed to compare community composition between Microcystis colony-attached and free-living bacteria, as well as among bacteria attached with Microcystis colonies of various sizes in culture. In the exponentially growing cyanobacterial cultures, Proteobacteria was the most dominant phylum in each colony-attached bacterial community, whereas Bacteroidetes was the most dominant phylum in each free-living bacterial community. The analysis using an indirect PCA model and Bray–Curtis dissimilarity index indicated that the dissimilarity between colony-attached and free-living bacterial communities was greater in the exponentially growing cyanobacterial cultures, and it became smaller in the stationary cultures of Microcystis. In the exponential growth phase of Microcystis, the relative abundance of Proteobacteria in colony-attached bacterial communities tended to decrease with decreasing colony size, whereas the relative abundance of Bacteroidetes in colony-attached bacterial communities tended to increase. In the exponential growth phase of Microcystis, the community composition dissimilarity among bacteria attached with Microcystis colonies of various sizes could be ranked in a descending order as follows: > 100 µm versus < 50 µm; 50–100 µm versus < 50 µm; and > 100 µm versus 50–100 µm. Our data indicated that the community composition of Microcystis colony-attached bacteria was different from that of free-living bacteria, and the colony size of Microcystis played an important role in structuring the community composition of Microcystis-attached bacteria.