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Multiple toxigenic and non-toxigenic species coexist in a bloom of the cyanobacterium Microcystis

Johansson, Emma LU orcid ; McLimans, Christopher J. ; Manoharan, Lokeshwaran LU orcid ; Mazur-Marzec, Hanna ; Tromas, Nicolas ; Pérez-Carrascal, Olga ; Legrand, Catherine ; Hambright, K. David ; Säll, Torbjörn LU and Ahrén, Dag LU orcid , et al. (2026) In Harmful Algae
Abstract
Freshwater blooms of the microcystin-producing (toxigenic) cyanobacterium Microcystis may cause severe damage to human health and the environment. However, toxigenic and non-toxigenic strains co-exist within single blooms, and microcystin concentration in the water varies throughout the season. We hypothesized that strains that produce and do not produce microcystins represent different genotypes. To this end, we combined microcystin analysis with genomic analyses of individual strains isolated from a natural bloom of the morphospecies Microcystis botrys. Whole-genome assemblies revealed high genomic diversity among 19 strains, representing five different genospecies. Ten strains had intact microcystin cluster with all ten genes (mcyA-J)... (More)
Freshwater blooms of the microcystin-producing (toxigenic) cyanobacterium Microcystis may cause severe damage to human health and the environment. However, toxigenic and non-toxigenic strains co-exist within single blooms, and microcystin concentration in the water varies throughout the season. We hypothesized that strains that produce and do not produce microcystins represent different genotypes. To this end, we combined microcystin analysis with genomic analyses of individual strains isolated from a natural bloom of the morphospecies Microcystis botrys. Whole-genome assemblies revealed high genomic diversity among 19 strains, representing five different genospecies. Ten strains had intact microcystin cluster with all ten genes (mcyA-J) present and the nine remaining strains lacked all mcy genes. All non-microcystin producing strains were members of a single genospecies, while the microcystin producers were distributed across four different genospecies. One strain had all ten genes present but detectable levels of microcystin were not measured, possibly due to phenotypic plasticity in gene expression or genetic inactivation. Overall, these results demonstrate that even single-morphospecies blooms, from a single time point, consist of multiple populations of genospecies, with different microcystin genotypes and phenotypes. These findings are of great value to the field as the two common observations, presence of toxigenic and non-toxigenic strains within a single bloom and seasonal succession of toxigenicity, can now be attributed to species co-existence and species succession. (Less)
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Contribution to journal
publication status
epub
subject
in
Harmful Algae
article number
103171
publisher
Elsevier
ISSN
1878-1470
DOI
10.1016/j.hal.2026.103171
language
English
LU publication?
yes
id
1e3cfbe2-0b05-458a-a5c1-5234cac4be84
date added to LUP
2026-06-29 10:52:28
date last changed
2026-06-29 13:20:18
@article{1e3cfbe2-0b05-458a-a5c1-5234cac4be84,
  abstract     = {{Freshwater blooms of the microcystin-producing (toxigenic) cyanobacterium Microcystis may cause severe damage to human health and the environment. However, toxigenic and non-toxigenic strains co-exist within single blooms, and microcystin concentration in the water varies throughout the season. We hypothesized that strains that produce and do not produce microcystins represent different genotypes. To this end, we combined microcystin analysis with genomic analyses of individual strains isolated from a natural bloom of the morphospecies Microcystis botrys. Whole-genome assemblies revealed high genomic diversity among 19 strains, representing five different genospecies. Ten strains had intact microcystin cluster with all ten genes (mcyA-J) present and the nine remaining strains lacked all mcy genes. All non-microcystin producing strains were members of a single genospecies, while the microcystin producers were distributed across four different genospecies. One strain had all ten genes present but detectable levels of microcystin were not measured, possibly due to phenotypic plasticity in gene expression or genetic inactivation. Overall, these results demonstrate that even single-morphospecies blooms, from a single time point, consist of multiple populations of genospecies, with different microcystin genotypes and phenotypes. These findings are of great value to the field as the two common observations, presence of toxigenic and non-toxigenic strains within a single bloom and seasonal succession of toxigenicity, can now be attributed to species co-existence and species succession.}},
  author       = {{Johansson, Emma and McLimans, Christopher J. and Manoharan, Lokeshwaran and Mazur-Marzec, Hanna and Tromas, Nicolas and Pérez-Carrascal, Olga and Legrand, Catherine and Hambright, K. David and Säll, Torbjörn and Ahrén, Dag and Rengefors, Karin}},
  issn         = {{1878-1470}},
  language     = {{eng}},
  month        = {{06}},
  publisher    = {{Elsevier}},
  series       = {{Harmful Algae}},
  title        = {{Multiple toxigenic and non-toxigenic species coexist in a bloom of the cyanobacterium Microcystis}},
  url          = {{http://dx.doi.org/10.1016/j.hal.2026.103171}},
  doi          = {{10.1016/j.hal.2026.103171}},
  year         = {{2026}},
}