Multilocus sequence typing (MLST) reveals high genetic diversity and clonal population structure of the toxic cyanobacterium Microcystis aeruginosa

• Published in: Microbiology (Society for General Microbiology) Vol. 153; no. 11; pp. 3695 - 3703
• Main Authors: Tanabe, Yuuhiko, Kasai, Fumie, Watanabe, Makoto M
• Format: Journal Article
• Language: English
• Published: Reading Soc General Microbiol 01.11.2007; Society for General Microbiology
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacterial Toxins - genetics; Bacterial Toxins - toxicity; Bacterial Typing Techniques; Bacteriology; Biological and medical sciences; Cyanobacteria; Cyanophyta; Evolution, Molecular; Fundamental and applied biological sciences. Psychology; Genes. Genome; Genetic Variation; Genetics; Genetics, Population; Linkage Disequilibrium; Microbiology; Microcystins - genetics; Microcystins - toxicity; Microcystis - classification; Microcystis - genetics; Microcystis aeruginosa; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; Phylogeny; Recombination, Genetic; Sequence Analysis, DNA; Japan; Microcystis aeruginosa; Typing; Bloom; Cyanobacteria; Bacteria; Genotype; Genetic diversity; Phylogeny; Population genetics
• DOI: 10.1099/mic.0.2007/010645-0
• ISSN: 1350-0872

1 Environmental Biology Division, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan 2 Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan Correspondence Makoto M. Watanabe makoto{at}biol.tsukuba.ac.jp Microcystis aeruginosa is one of the most prevalent bloom-forming cyanobacteria and has been the cause of increasing public health concern due to the production of hepatotoxins (microcystins). To investigate the genetic diversity, clonality and evolutionary genetic background with regard to the toxicity of M. aeruginosa , a multilocus sequence typing (MLST) scheme was developed, based on seven selected housekeeping loci ( ftsZ , glnA , gltX , gyrB , pgi , recA and tpi ). Analysis of a collection of 164 isolates from Japan and other countries identified 79 unique sequence types (STs), revealing a high level of genetic diversity ( H =0.951). Although recombination between loci was indicated to be substantial by Shimodaira–Hasegawa (SH) tests, multilocus linkage disequilibrium analyses indicated that recombination between strains probably occurs at some frequency but not to the extent at which alleles are associated randomly, suggesting that the population structure of M. aeruginosa is clonal. Analysis of subsets of strains also indicated that the clonal population structure is maintained even in a local population. Phylogenetic analysis based on the concatenated sequences of seven MLST loci demonstrated that microcystin-producing genotypes are not monophyletic, providing further evidence for the gain and loss of toxicity during the intraspecific diversification of M. aeruginosa . However, toxic strains are genetically distinct from non-toxic strains in MLST allelic profiles, and it was also shown that non-toxic strains harbouring toxin genes fall into a single monophyletic clade, except for one case. These results suggest that the toxicity of M. aeruginosa is relatively stable in the short term, and therefore can be unequivocally characterized by MLST. The MLST scheme established here will be of great help for future detailed population genetic studies of M. aeruginosa . Abbreviations: I A , index of association; LC ESI-MS, liquid chromatography electrospray ionization MS; ML, maximum-likelihood; MLST, multilocus sequence typing; NJ, neighbour-joining; NJBP, NJ bootstrap; PP, posterior probability; r D , standardized measure of I A ; SH test, Shimodaira–Hasegawa test; ST, sequence type The GenBank/EMBL/DDBJ accession numbers for the ftsZ , glnA , gltX , gyrB , pgi , recA and tpi sequences of the Microcystis aeruginosa strains examined in this study are AB324850–AB325402. A supplementary figure showing the individual phylogenetic trees for the seven MLST loci, and supplementary tables showing strain information and the degenerate primer sequences used for isolating five of the seven MLST genes, are available with the online version of this paper.