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Microcystins (MCs) are a group of cyclic heptapeptide hepatotoxins produced by cyanobacteria.
Among 70 analogues of MCs, Microcystin-LR (MC-LR) is the dominant type in Sri Lankan water bodies.
Contamination of MC-LR in drinking water is a serious health issue. Thus, the present study was carried
out to identify freshwater bacteria, which are capable of degrading MC-LR. BIOLOG MT2 plate assay was
employed to confirm MC-LR biodegradation by the bacterium Bacillus cereus and Rahnella aquatilis which
were isolated from Girandurukotte reservoir and form Ulhitiya reservoir respectively. Classic batch culture
experiments showed that B. cereus and R. aquatilis removed 100% of MC-LR at 28o
C within 8 and 10 days
of incubation respectively. Optimized biodegradation conditions for MC-LR by B. cereus and R. aquatilis were
recorded at 320
C when phosphates and nitrate concentrations were 0.01ppm and 0.4 ppm respectively in
experimental medium. Moreover, B. cereus andR. aquatilis were capable of degrading other MCs analogues;
Microcystin-LF (MC-LF), Microcystin –LW (MC-LW), Microcystin –RR (MC-RR) and nodularin (NOD) as
well. Molecular studies confirmed that B. cereus and R. aquatilis harbored MC degrading mlrA, mlrB, mlrC
and mlrD genes. This is the first record for degradation of MCs and NOD by R. aquatilis.
