Assessment of estrogenic potential from exudates of microcystin-producing and non-microcystin-producing Microcystis by metabolomics, machine learning and E-screen assay.

Cyanobacterial blooms, often dominated by Microcystis aeruginosa, are capable of producing estrogenic effects. It is important to identify specific estrogenic compounds produced by cyanobacteria, though this can prove challenging owing to the complexity of exudate mixtures. In this study, we used untargeted metabolomics to compare components of exudates from microcystin-producing and non-microcystin-producing M. aeruginosa strains that differed with respect to their ability to produce microcystins, and across two growth phases. We identified 416 chemicals and found that the two strains produced similar components, mainly organoheterocyclic compounds (20.2%), organic acids and derivatives (17.3%), phenylpropanoids and polyketides (12.7%), benzenoids (12.0%), lipids and lipid-like molecules (11.5%), and organic oxygen compounds (10.1%). We then predicted estrogenic compounds from this group using random forest machine learning. Six compounds (daidzin, biochanin A, phenylethylamine, rhein, o-Cresol, and arbutin) belonging to phenylpropanoids and polyketides (3), benzenoids (2), and organic oxygen compound (1) were tested and exhibited estrogenic potency based upon the E-screen assay. This study confirmed that both Microcystis strains produce exudates that contain compounds with estrogenic properties, a growing concern in cyanobacteria management.

Non-microcystin extracellular metabolites of Microcystis aeruginosa impair viability and reproductive gene expression in rainbow trout cell lines.

Microcystis aeruginosa is a ubiquitous freshwater cyanobacterium best known for producing hepatotoxic microcystins; however, this common bloom-forming species also produces myriad biologically active and potentially deleterious other metabolites. Our understanding of the effects of these non-microcystin metabolites on fish is limited. In this study, we evaluated cytotoxicity of extracellular metabolites harvested from both microcystin-producing (MC+) and non-producing (MC-) strains of M. aeruginosa on rainbow trout (Oncorhynchus mykiss) cell lines derived from tissues of the brain, pituitary, heart, gonads, gills, skin, liver, and milt. We also examined the influence of M. aeruginosa exudates (MaE) on the expression of critical reproduction-related genes using the same cell lines. We found that exudates of the MC- M. aeruginosa strain significantly reduced viability in RTBrain, RTgill-W1, and RT-milt5 cell lines and induced significant cellular stress and/or injury in six of the eight cell lines-highlighting potential target tissues of cyanobacterial cytotoxic effects. Observed sublethal consequences of Microcystis bloom exposure occurred with both MC+ and MC- strains' exudates and significantly altered expression of developmental and sex steroidogenic genes. Collectively, our results emphasize the contributions of non-MC metabolites to toxicity of Microcystis-dominated algal blooms and the need to integrate the full diversity of M. aeruginosa compounds-beyond microcystins-into ecotoxicological risk assessments.

Cyanobacteria blooms induce embryonic heart failure in an endangered fish species.

Cyanobacterial blooms drive water-quality and aquatic-ecosystem deterioration in eutrophic lakes worldwide, mainly owing to their harmful, secondary metabolites. The response of fish exposed to these cyanobacterial chemicals, however, remains largely unknown. In this paper, we employed an endangered fish species (Sinocyclocheilus grahami) in Dianchi Lake, China to evaluate the risks of cell-free exudates (MaE) produced by a dominant cyanobacterium (Microcystis aeruginosa) on embryo development, as well as the molecular mechanisms responsible. MaE (3d cultured) caused a reduction of fertilization (35.4%) and hatching (15.5%) rates, and increased mortality rates (≤90.0%) and malformation rate (27.6%), typically accompanied by heart failure. Proteomics analysis revealed that two greatest changed proteins - protein S100A1 (over-expressed 26 times compared with control) and myosin light chain (under-expressed 25 fold) - are closely associated with heart function. Further study revealed that heart failure was due to calcium ion imbalance and malformed cardiac structure. We conclude that harmful secondary metabolites from cyanobacteria may adversely affect embryo development in this endangered fish, and possibly contribute to its disappearance and unsuccessful recovery in Dianchi Lake. Hazardous consequences of substances released by cyanobacteria should raise concerns for managers addressing recovery of this and other imperiled species in affected lakes.