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

Microcystis colonies typically undergo vertical migration in water. However, some small Microcystis colonies suspended in the lower water layer lose their ability to migrate, gradually disaggregate, and eventually decay. The composition of epiphytic bacterial communities associated with Microcystis colonies in the upper and lower water layers of an aquaculture pond was compared. A dominant Flavobacterium strain was isolated from the lower epiphytic bacteria community, and its colony-degrading potential and CAZyme-encoding genes were analyzed. The results showed significant difference in the composition between upper and lower epiphytic bacterial communities. The relative abundance of Flavobacterium in the lower epiphytic community was 7.91 times higher than that in the upper community (P<0.001). The isolated strain was identified and named F. columnare TN-1. This strain significantly reduced Microcystis colony density, the area of individual colonies and extracellular polysaccharide (EPS) content of each Microcystis cell (P<0.05). Genomic analysis of TN-1 identified 274 CAZyme-encoding genes, accounting for 8.5% of the total gene count. These included 143 glycosyltransferase (GT) genes, 63 glycoside hydrolase (GH) genes, 42 carbohydrate-binding module (CBM) genes, 19 carbohydrate esterase (CE) genes, 3 auxiliary activity (AA) genes, and 4 polysaccharide lyase (PL) genes. F. columnare TN-1 demonstrated the ability to degrade EPS of Microcystis colonies, leading to their disaggregation.