Correlation between Expression of <i>mcy</i> Gene Cluster Relevant to Microcystin Production and Cell Cycle of <i>Microcystis viridis</i>

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  • UTSUMI MOTOO
    Graduate School of Life and Environmental Sciences, University of Tsukuba
  • KAMEYAMA KEISHI
    Research institute for health fundamentals, Ajinomoto Co., Inc.
  • OKANO KUNIHIRO
    Department of Biological Environment, Akita Prefectural University
  • SUGIURA NORIO
    Graduate School of Life and Environmental Sciences, University of Tsukuba

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  • <i>Microcystis viridis</i>におけるmicrocystin産生遺伝子群<i>mcy</i>の発現と細胞周期との関係
  • Correlation between expression of mcy gene cluster relevant to microcystin production and cell cycle of microcystis viridis

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Abstract

Microcystin, a hepatotoxin produced by cyanobacteria Microcystis species, is biosynthesized nonribosomally by a multifunctional enzyme complex. The enzyme is composed of peptide synthetase and polyketide synthase coded by the mcy gene cluster. Especially, mcyB and mcyD are representative for microcystin biosynthesis genes of peptide synthetase and polyketide synthase, respectively. The effect of cell growth or cell cycle on the toxin biosynthesis of Microcystis has not been clarified. The purpose of this study is to elucidate when the microcystins are synthesized and accumulated in the cell and how intracellular microcystins act in the cell. We examined the transcript levels of mcyB and mcyD under nitrate starved synchronous culture of axenic strain Microcystis viridis NIES－102. Both the gene transcript levels could be observed with the proportion of the cells in S－phase. Then, microcystins were highly contained when the proportion of G2/M－phase cells was the highest value in culture medium. Furthermore, it was indicated that pyrogallol, which was an allelopathic compound produced by macrophytes such a genus Myriophyllom, inhibited the expression of the mcyD genes in M. viridis. These results suggested that the microcystin biosynthesis were closely correlated with the cell cycle in the toxin-producing cyanobacteria.

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