This site needs JavaScript to work properly. Please enable it to take advantage of the complete set of features!
Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

NIH NLM Logo
Log in
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2009 May 22:9:115.
doi: 10.1186/1471-2148年9月11日5.

Recombination, cryptic clades and neutral molecular divergence of the microcystin synthetase (mcy) genes of toxic cyanobacterium Microcystis aeruginosa

Affiliations

Recombination, cryptic clades and neutral molecular divergence of the microcystin synthetase (mcy) genes of toxic cyanobacterium Microcystis aeruginosa

Yuuhiko Tanabe et al. BMC Evol Biol. .

Abstract

Background: The water-bloom-forming cyanobacterium Microcystis aeruginosa is a known producer of various kinds of toxic and bioactive chemicals. Of these, hepatotoxic cyclic heptapeptides microcystins have been studied most intensively due to increasing concerns for human health risks and environmental damage. More than 70 variants of microcystins are known, and a single microcystin synthetase (mcy) gene cluster consisting of 10 genes (mcyA to mcyJ) has been identified to be responsible for the production of all known variants of microcystins. Our previous multilocus sequence typing (MLST) analysis of the seven housekeeping genes indicated that microcystin-producing strains of M. aeruginosa are classified into two phylogenetic groups.

Results: To investigate whether the mcy genes are genetically structured similarly as in MLST analysis of the housekeeping genes and to identify the evolutionary forces responsible for the genetic divergence of these genes, we used 118 mcy-positive isolates to perform phylogenetic and population genetic analyses of mcy genes based on three mcy loci within the mcy gene cluster (mcyD, mcyG, and mcyJ), none of which is involved in the production of different microcystin variants. Both individual phylogenetic analysis and multilocus genealogical analysis of the mcy genes divided our isolates into two clades, consistent with the MLST phylogeny based on seven housekeeping loci. No shared characteristics within each clade are known, and microcystin analyses did not identify any compositional trend specific to each clade. Statistical analyses for recombination indicated that recombination among the mcy genes is much more frequent within clades than between, suggesting that recombination has been an important force maintaining the cryptic divergence of mcy genes. On the other hand, a series of statistical tests provided no strong evidence for selection to explain the deep divergence of the mcy genes. Furthermore, analysis of molecular variance (AMOVA) indicated a low level of geographic structuring in the genetic diversity of mcy.

Conclusion: Our phylogenetic analyses suggest that the mcy genes of M. aeruginosa are subdivided into two cryptic clades, consistent with the phylogeny determined by MLST. Population genetic analyses suggest that these two clades have primarily been maintained as a result of homology-dependent recombination and neutral genetic drift.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Structure of the microcystin synthetase (mcy) gene and microcystins. Structural representation of microcystin variants and the microcystin synthetase (mcy) gene cluster [5]. General numbering of amino acids is indicated in gray. Arrows indicate the proposed involvement of the product of each mcy marker locus in the incorporation and/or modification of each amino acid into the microcystin. Note that the amino acids (X and Z) and groups (R1) highlighted in gray are variable. Microcystin is abbreviated as "MCY" in the right-hand table. Abbreviations for three uncommon amino acids in microcystins are as follows: D-MeAsp, D-erythro-β-methylaspartic acid; Adda, (2S, 3S, 8S, 9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid; MdhA, N-methyldehydroalanine. The positions of PCR primers in the mcy genes are indicated by a gray box.
Figure 2
Figure 2
Phylogenetic analysis of the seven housekeeping genes (MLST). Neighbor-joining (NJ) phylogenetic tree of 102 STs of M. aeruginosa based on the concatenated sequences of the seven MLST loci. Branches supported by both NJ bootstrap probabilities (NJBP > 75%) and Bayesian posterior probabilities (PP > 0.85) are highlighted by thick bars. Statistical values for these branches are indicated (NJ BP, PPx100).
Figure 3
Figure 3
Neighbor-joining tree of mcy genes. Phylogenetic relationships among the 51 mcySTs of M. aeruginosa based on the NJ analysis of the individual mcy loci. Statistical values for the branch of the group A-B boundary (in bold) are indicated (NJ bootstrap [NJBP]/[Bayesian PP] ×ばつ 100). In general, within-group relationships were poorly resolved; branches with NJBP > 75% are highlighted in bold and NJBP values are shown.
Figure 4
Figure 4
ClonalFrame analysis of mcy genes. (a) A ClonalFrame genealogy of the 51 mcySTs inferred from the three mcy loci. (b) Genetic representation of the recombination events at the branch of a (red) and b (blue) in the mcy genealogy. X-axis indicates the nucleotide position in the respective mcy loci. Y-axis indicates the posterior probability of recombination.
Figure 5
Figure 5
Microcystin composition. Distribution of microcystin variants in groups A, B, and ''X'' (putative hybrid mcySTs: mcyST10, mcyST11, mcyST24, and mcyST46). Abbreviations for the microcystin variants are as follows: LR, microcystin-LR; RR, microcystin-RR; YR, microcystin-YR; dLR, [Dha7]microcystin-LR; dRR, [Dha7]microcystin-RR; dYR, [Dha7]microcystin-YR; ND, not detected.

References

    1. Dittmann E, Wiegand C. Cyanobacterial toxins–occurrence, biosynthesis and impact on human affairs. Mol Nutr Food Res. 2006;50:7–17. - PubMed
    1. Codd GA, Lindsay J, Young FM, Morrison LF, Metcalf JS. Harmful cyanobacteria: from mass mortalities to management measures. In: Huisman J, Matthijs HCP, Visser PM, editor. Harmful cyanobacteria. Dordrecht, The Netherlands: Springer; 2005. pp. 1–24.
    1. Kurmayer R, Dittmann E, Fastner J, Chorus I. Diversity of microcystin genes within a population of the toxic cyanobacterium Microcystis spp. in Lake Wannsee (Berlin, Germany) Microb Ecol. 2002;43:107–118. - PubMed
    1. Nishizawa T, Asayama M, Fujii K, Harada K, Shirai M. Genetic analysis of the peptide synthetase genes for a cyclic heptapeptide microcystin in Microcystis spp. J Biochem. 1999;126:520–529. - PubMed
    1. Tillett D, Dittmann E, Erhard M, von Döhren H, Börner T, Neilan BA. Structural organization of microcystin biosynthesis in Microcystis aeruginosa PCC7806: an integrated peptide-polyketide synthetase system. Chem Biol. 2000;7:753–764. - PubMed

Publication types

LinkOut - more resources

Full text links
BioMed Central full text link BioMed Central Free PMC article
Cite

AltStyle によって変換されたページ (->オリジナル) /