Determination of microcystin-LR degrading gene mlrA in biofilms at a biological drinking water treatment facility

Biological treatment methods used in water purification plants help degrade the cyanotoxin microcystin. The microcystin degraders in the aggregated microbial communities of biofilms in biological treatment facilities have not been previously investigated by molecular analysis. In the present study, the bacteria relevant to microcystin degradation and the gene encoding the microcystin-degrading enzyme MlrA were investigated in the biofilms of a biological drinking water treatment facility. Based on phylogenetic analyses of the 16S rRNA genes and mlrA, microcystin-degrading bacterial species were present in these biofilms and these bacteria possessed mlrA homologues. The deduced MlrA amino acid sequences had high sequence homology with previously reported MlrA enzymes. Non-culturable microcystin-degrading bacteria were found in the biofilms throughout the sampling period. This biological water treatment seems be a suitable method for the removal of microcystin by microcystin-degrading bacteria.