The mosaic structure of the mcyABC operon in Microcystis

University of Oslo, Department of Molecular Biosciences, 0316 Oslo, Norway.
Microbiology (Impact Factor: 2.84). 08/2008; 154(Pt 7):1886-99. DOI: 10.1099/mic.0.2007/015875-0
Source: PubMed

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.


Available from: Ave Tooming-Klunderud, Apr 01, 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Historic samples of phytoplankton can provide information on the abundance of the toxigenic genotypes of cyanobacteria in dependence on increased or decreased eutrophication. The analysis of a time-series from preserved phytoplankton samples by quantitative PCR (qPCR) extends observation periods considerably. The analysis of DNA from heat-desiccated samples by qPCR can be aggravated by point substitutions or the fragmentation of DNA introduced by the high temperature. In this study, we analyzed whether the heat desiccation of the cellular material of the cyanobacterium Planktothrix sp. introduced potential errors to the template DNA that is used for qPCR within (i) 16S rDNA and phycocyanin genes and (ii) the mcyA gene indicative of the incorporation of either dehydrobutyrine (Dhb) or N-methyl-dehydroalanine (Mdha) in position 7, and (ii) the mcyB gene, which is indicative of homotyrosine (Hty) in position 2 of the microcystin (MC) molecule. Due to high temperature desiccation, the deterioration of the DNA template quality was rather due to fragmentation than due to nucleotide substitutions. By using the heat-desiccated samples of Lake Zürich, Switzerland the abundance of the Dhb, Mdha and Hty genotypes was determined during three decades (1977-2008). Despite major changes in the trophic state of the lake resulting in a major increase of the total Planktothrix population density, the proportion of these genotypes encoding the synthesis of different MC congeners showed high stability. Nevertheless, a decline of the most abundant mcyA genotype indicative of the synthesis of Dhb in position 7 of the MC molecule was observed. This decline could be related to the gradual incline in the proportion of a mutant genotype carrying a 1.8kbp deletion of this gene region. The increase of this mcyA (Dhb) gene deletion mutant has been minor so far, however, and likely did not affect the overall toxicity of the population.
    PLoS ONE 11/2013; 8(11):e80177. DOI:10.1371/journal.pone.0080177 · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Planktothtrix agardhii (Oscillatoriales) is a filamentous cyanobacterium, which frequently forms blooms in shallow, polymictic and eutrophicated waters. This species is also a rich source of unique linear and cyclic peptides. In the current study, the profile of the peptides in samples from the P. agardhii-dominated Siemianówka Dam Reservoir (SDR) (northeast Poland) was analyzed for four subsequent years (2009-2012). The LC-MS/MS analyses revealed the presence of 33 peptides. Twelve of the most abundant ones, including five microcystins, five anabaenopeptins, one aeruginosin and one planktocyclin, were present in all field samples collected during the study. The detection of different peptides in two P. agardhii isolates indicated that the SDR population was composed of several chemotypes, characterized by different peptide patterns. The total concentration of microcystins (MCs) positively correlated with the biomass of P. agardhii. Between subsequent years, the changes in the ratio of the total MCs concentration to the biomass of P. agardhii were noticed, but they were less than threefold. This is the first study on the production of different classes of non-ribosomal peptides by freshwater cyanobacteria in Poland.
    Archives of Microbiology 06/2014; DOI:10.1007/s00203-014-1008-9 · 1.86 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Several gene clusters that are responsible for toxin synthesis in bloom-forming cyanobacteria have been found to be associated with transposable elements (TEs). In particular, insertion (IS) elements were shown to play a role in the inactivation or recombination of the genes responsible for cyanotoxin synthesis. Plasmids have been considered as important vectors of IS element distribution to the host. In this study, we aimed to elucidate the IS elements propagated on the plasmids and the chromosome of the toxic cyanobacterium Planktothrix agardhii NIVA-CYA126/8 by means of high throughput sequencing. In total, five plasmids (pPA5.5, 14, 50, 79, 115 kbp) were elucidated and two plasmids (pPA5.5, 115 kb) were found to propagate full IS element copies. Large stretches of shared DNA information between plasmids were constituted of TEs. Two plasmids (pPA5.5, 14 kbp) were used as candidates for engineering shuttle vectors (named pPA5SV, pPA14SV) in vitro by PCR amplification and the subsequent transposition of the Tn5 cat transposon, including the R6Kγ origin of replication of E. coli. While pPA5SV was found fully segregated, pPA14SV consistently co-occurred with its wild type plasmid even under the highest selective pressure. Interestingly, the Tn5 cat transposon became transferred by homologous recombination into another plasmid pPA50. The availability of shuttle vectors is considered to be of relevance in investigating the genome plasticity as a consequence of homologous recombination events. Combining the potential of high throughout sequencing and in vitro production of shuttle vectors makes it simple to produce species-specific shuttle vectors for many cultivable prokaryotes.
    Applied and Environmental Microbiology 06/2014; 80(16). DOI:10.1128/AEM.01188-14 · 3.95 Impact Factor