Biodegradation of microcystins by microbiota of duckweed Spirodela polyrhiza

Cyanobacteria-produced allelochemicals, including hepatotoxic microcystins (MCs), exert an inhibitory effect on macrophyte growth. However, the role of macrophyte-associated bacteria and algae (macrophyte microbiota) in mitigating these immediate negative effects of cyanotoxins remains poorly understood. In this paper, we analyzed the biodegradation of microcystin-RR, MC-LR, and MC-LF by microbiota of the macrophyte Spirodela polyrhiza. The biodegradation of two MC variants was observed and LC-MS/MS analysis allowed identifying the degradation products of MC-RR (m/z 1011, 984, 969, 877, 862, 820, and 615) and MC-LR (m/z 968 and 953), including eight previously unreported products. No degradation products of MC-LF were detected, suggesting its stability and resistance under experimental conditions. NGS-based profiling of microbial consortia revealed no major differences in bacterial community composition across experimental treatments. Taxa previously reported as capable of MC degradation have been found in S. polyrhiza microbiota. Furthermore, the presence of genes encoding putative microcystinase homologues and the formation of new linear intermediates suggest a biochemical pathway that is similar, but not identical to previously reported. The ability of aquatic plant microbiota to biodegrade MCs holds environmental significance, and further studies in this field are required.