The mosaic structure of the mcyABC operon in Microcystis

Abstract

An extensive study of the mcyABC genes and regions flanking the mcy gene cluster was performed in naturally occurring Microcystis strains. Lack of methylation in strains producing only desmethyl 7 -microcystin was found to be associated with point mutations in substrate-binding sequence motifs of the N-methyltransferase (NMT) domain in McyA. Multiple recombination events giving rise to 'phylogenetic mosaics' were detected within the NMT-domain-encoding mcyA sequences and the adenylation (A) domain sequences of mcyB and mcyC. Recombination leading to exchanges between the mcyB and mcyC regions encoding A domains in modules McyB1 and McyC was also detected. A previously reported replacement of the A domain in McyB1 was found to involve the region between the conserved motifs A3 and A8/A9. In all microcystin-producing strains the mcy gene cluster was flanked by the genes uma1 and dnaN. Clear indications of recombination, an insertion element and footprints of IS elements were found in the dnaN-mcyJ intergenic region. Among the non-microcystin producers, uma1 and dnaN were linked in some, but not all strains. Most non-producing strains lacked all mcy genes, while one strain possessed a partially deleted mcy operon. Our results show that frequent horizontal gene transfer events in addition to point mutations and insertions/deletions contribute to variation in the mcy gene cluster.

The cylindrospermopsin gene cluster of Aphanizomenon sp. strain 10E6: organization and recombination

“…For the mcy genes, it has been shown that the operon structure and the order of genes varies between the genera Planktothrix, Anabaena and Microcystis (reviewed by Dittmann & Börner, 2005). In addition, recombination between different domains within the mcy gene clusters, point mutations and deletion of gene regions, as well as lack of substrate specificity of A-domains have been shown to contribute to the synthesis of different microcystin isoforms (Fewer et al, 2008;Mikalsen et al, 2003;Tooming-Klunderud et al, 2008). A deletion within the second module of mcyA and the first module of mcyB resulted in the synthesis of another cyanotoxin, nodularin (Moffitt & Neilan, 2004;Rantala et al, 2004).…”

Genetic analysis of the microcystin biosynthesis gene cluster in Microcystis strains from four bodies of eutrophic water in Japan

“…Interestingly, the genome database showed that 688 kb, equivalent to 11.8% of the entire genome, was composed of both ISs of thirty-fi ve groups and MITEs of eight groups. ISMae7 (direct repeat, TTGATAA) was observed within the dnaN-mcyJ non-coding region near the trp2 gene (T. Tooming-Klunderud et al, 2008). Besides, strain B-47 and M. viridis NIES-112 and 113 possessed a transposase gene between the dnaN and mcyJ intergenic region (T. .…”

“…This result indicates that neither insert of dnaN-mcyJ non-coding region nor that of mcyC-uma1 non-coding region has infl uence on the transcription of mcy. Recent results showed that the genus Microcystis strains including a gene insertion within either dnaN-mcyJ or mcyC-uma1 non-coding region retained the MCYST productivity (T. Tooming-Klunderud et al, 2008). We judged both type B and type C as the MCYST-producer Microcystis from HPLC analysis.…”

“…Besides, strain B-47 and M. viridis NIES-112 and 113 possessed a transposase gene between the dnaN and mcyJ intergenic region (T. . Tooming- Klunderud et al (2008) reported that in a culture of M. aeruginosa NIVA-CYA 143, from the Norwegian Institute for Water Research Cyanobacterial Culture Collection, the loss of mcyDEFGHIJ was identifi ed based on a PCR assay and genomic Southern hybridization. The mcyDEFGHIJ-deleted strain lost the N-methyltransferase domain, involved in the putative N-methylation of amino acids (Nishizawa et al, 1999), in the McyA NRPS modules (Tooming-Klunderud et al, 2008).…”

“…We presume that recombination occurred in the mcy gene cluster frequently in the genus Microcystis. However, in the studies of T. and Tooming-Klunderud et al (2008), the diversity of the mcy gene was investigated in Microcystis strains in the laboratory.…”