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Applied and Environmental Microbiology, July 2005, p. 3453-3457, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3453-3457.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Polyketide Synthase Gene Responsible for Citrinin Biosynthesis in Monascus purpureus

International Center for Biotechnology, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan,¹ YAEGAKI Technology Development Laboratories, YAEGAKI Bio-Industry, Inc., 681 Mukudani, Hayashida-cho, Himeji 679-42, Japan²

Received 17 March 2004/ Accepted 13 January 2005

Citrinin produced by Aspergillus, Penicillium, and Monascus species is a polyketide compound that has nephrotoxic activity in mammals and is bactericidal toward gram-positive bacteria. To avoid the risk of citrinin contamination in other fermentation products produced by Monascus purpureus, knowledge of the citrinin biosynthetic genes is needed so that citrinin-nonproducing strains can be generated. We cloned a polyketide synthase (PKS) gene from M. purpureus with degenerate primers designed to amplify the conserved region of a ketosynthase domain of a fungal PKS. A 13-kb genomic DNA fragment was identified that contained a full-length PKS gene (pksCT) of 7,838 bp with a single 56-bp intron. pksCT encodes a 2,593-amino-acid protein that contains putative domains for ketosynthase, acyltransferase, acyl carrier protein (ACP), and a rare methyltransferase. There was no obvious thioesterase domain, which usually is downstream of the ACP domain in multi-aromatic-ring PKSs. pksCT transcription was correlated with citrinin production, suggesting that the pksCT gene product was involved in citrinin biosynthesis. Homologous recombination between the wild-type allele and a truncated disruption construct resulted in a pksCT-disrupted strain of M. purpureus. The disruptant did not produce citrinin, but a pksCT revertant generated by successive endogenous recombination events in the pksCT disruptant restored citrinin production, indicating that pksCT encoded the PKS responsible for citrinin biosynthesis in M. purpureus.

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