Phylogenetic relationships and genetic divergence of paralytic shellfish toxin- and cylindrospermopsin- producing Cylindrospermopsis and raphidiopsis

Harmful Algae. 2020 Mar;93:101792. doi: 10.1016/j.hal.2020.101792. Epub 2020 Mar 18.

Abstract

Cylindrospermopsis and Raphidiopsis (C/R group) are closely related species responsible for cyanobacterial blooms worldwide. Paralytic shellfish toxins (PSTs) and cylindrospermopsins (CYNs) have been identified in different C/R group strains. However, the evolutionary relationship between PST- and CYN-producing strains has not been systematically evaluated. In this study, C/R group strains and their toxin biosynthesis genes were evaluated by phylogenetic analysis and sequence comparison. None of the tested strains are able to produce PSTs and CYNs simultaneously. The C/R group strains were clustered into five clades, including two non-toxic, two CYN-producing and one PST-producing clades. A high degree of similarity was observed for rpoC1 (> 96%) and ITS-L (> 97%) sequences within each clade with the exception of the ITS-L (87% to 100%) region in CYN-producing R. curvata, which has been shown to contain variable sequence insertions. Genomic analysis revealed that sxtY and sxtZ could be found in both toxic and non-toxic strains. The transposase gene IS4 was only observed in strains from the PST-producing clade. The sxt and cyr gene clusters share five gene families with similar functions. The amino acid sequences of the adenylyl-sulfate kinase genes, sxtO and cyrN, are more similar (45% to 81%) than other pairs of genes (8.0% to 40%). SxtO and CyrN proteins from C/R group strains forms an independent clade on the phylogenetic tree with a high degree of sequence similarity (78% to 100%). In conclusion, PST- and CYN- producing C/R group species can be classified into different clades based on their phylogenetic profile. The sxtO and cyrN genes have probably diverged from a single ancestral adenylyl-sulfate kinase gene, and may be specifically used for toxin biosynthesis in C/R group species.

Keywords: Biosynthesis; Cyanotoxin; Cylindrospermopsin; Gene cluster; Phylogeny; Saxitoxin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkaloids
  • Bacterial Toxins* / genetics
  • Cylindrospermopsis*
  • Phylogeny
  • Shellfish
  • Uracil / analogs & derivatives

Substances

  • Alkaloids
  • Bacterial Toxins
  • cylindrospermopsin
  • Uracil