Effect of Microcystin and Its Degradation Products on the Transcription of Genes Encoding Microcystin Degrading Enzymes

Abstract

It is known that mlrA, mlrB and mlrC encode microcystin (MC)-degrading enzymes in MC－degrading bacteria. We discovered the mechanism by which transcription of these genes was induced in MC-degrading bacterium Sphingopyxis sp. C－1. We showed induction of the transcription of mlrA, mlrB and mlrC by microcystin－LR (MCLR) and that of mlrA and mlrB by MCLR degradation products (linear microcystin, H－Adda－Glu－Mdha－Ala－OH (tetra peptide) and 2S, 3S, 8S, 9S－3－amino－9－methoxy－2, 6, 8－trimetyl－10－phenyldeca－4E, 6E－dienoic acid (Adda)). Adda played a key role in the induction of transcription of mlrA and mlrB, while the cyclic structure of MCLR was important for the induction of transcription of mlrC. It was found that the MC-degrading bacteria responded to MCLR and its degradation products by degrading microcystin through a sequential chain reaction for expression of MlrA, MlrB and MlrC.