Flavobacterium isolated from epiphytic bacteria of Microcystis: colony-degrading potential and analysis of CAZyme-encoding genes

Microcystis blooms frequently occur in eutrophic freshwater bodies, where epiphytic bacteria interact with Microcystis colonies through cooperative or competitive relationships. Declining colonies are sedentary and are always found in the lower water layer, whereas healthy, mobile colonies reside exclusively in the upper layer. In this study, we compared the composition of epiphytic bacterial communities associated with Microcystis colonies in the upper and lower water layers of an aquaculture pond. A dominant Flavobacterium strain was isolated from the lower epiphytic bacterial community, and its colony-degrading potential and carbohydrate-active enzyme (CAZyme)-encoding genes were analyzed. The results showed significant differences in community composition between the upper and lower epiphytic bacterial communities. Compared to the upper epiphytic bacterial community, the relative abundance of Flavobacterium in the lower community increased by 691%, whereas that of Cetobacterium decreased by 92.84%. The dominant Flavobacterium strain isolated from the lower community was identified as F. columnare TN-1. When Microcystis colonies were treated with F. columnare TN-1 for 12 h, both the size of individual colonies and the extracellular polysaccharide (EPS) content per cell significantly decreased, indicating that F. columnare TN-1 could degrade Microcystis EPS and lead to colony disaggregation. Genomic analysis revealed that F. columnare TN-1 harbors 274 CAZyme-encoding genes, representing 8.5% of its total gene repertoire, including glycoside hydrolase and polysaccharide lyase family members implicated in EPS degradation.