Still challenging: the ecological function of the cyanobacterial toxin microcystin – What we know so far

Abstract

Microcystins (MCs) are the most commonly studied cyanotoxins. While these past studies have mainly focused on the toxicity of MCs, the evolutionary history of life has shown that toxicity can be considered as an assigned role to MCs. Nowadays, there is a growing interest in understanding the importance of cyanotoxins in any of the physiological processes or beyond at the ecological level. This review evaluates the variously proposed intracellular and extracellular functions of MCs and how they benefit the producing cyanobacterium. However, the strain-specific and divergent laboratory and field results obtained to date have made it difficult to generalize.Recent studies demonstrated a correlation between dissolved inorganic carbon (DIC) and the growth and MC production of M. aeruginosa. In a competitive study, the effect of low and high DIC (0.365 and 7.658 mmol l -1 KHCO3) on M. aeroginosa toxic and non-toxic strains, FACHB 912 and FACHB 469, co-cultured with green algae Chlamydomonas microsphaera were investigated. The growth of M. aeruginosa toxic and non-toxic strains was negatively affected by DIC without any significant changes in the chlorophyll content; however, the photosynthesis efficiency and chlorophyll content of green algae decreased. The results proposed that M. aeruginosa might be more adapted to low DIC condition (Zhang et al. 2012). Increased dissolved inorganic carbon had an adverse effect on the frequency of toxic Microcystis and MCs concentration in Lake Chaohu, China as well (Yu et al. 2014). Deficiency of intracellular inorganic carbon resulted in an increase in MC production of M. aeruginosa PCC 7806. Moreover, the toxic

A Review on the Study of Cyanotoxins in Paleolimnological Research: Current Knowledge and Future Needs

“…These timescales imply that cyanobacterial toxins play ecological role(s) other than grazer defense, and that their toxicity towards zooplankton may only be an indirect effect of their production and release into the water column. Cyanotoxin biological function still remains a subject of debate and various hypotheses, derived mostly from experimental observations, on their potential intra-and extracellular roles have been put forward [1,[12][13][14].…”

“…These timescales imply that cyanobacterial toxins play ecological role(s) other than grazer defense, and that their toxicity towards zooplankton may only be an indirect effect of their production and release into the water column. Cyanotoxin biological function still remains a subject of debate and various hypotheses, derived mostly from experimental observations, on their potential intra-and extracellular roles have been put forward [1,[12][13][14].Like the ecological role of cyanobacterial metabolites, the environmental triggers causing toxin production lack definite identification in experimental and monitoring investigations. Nutrients, frequently associated with cultural eutrophication (nitrogen and phosphorus) in freshwaters, have been identified as key drivers of toxin production [15], but cyanobacteria in selected hypereutrophic systems do not produce cyanotoxins [1].…”

Demonstrated transfer of cyanobacteria and cyanotoxins along a freshwater-marine continuum in France

“…The general structure of that cyclic heptapeptide includes a specific beta amino acid-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadienoic acid -Adda (Ortiz et al, 2017;Tillett et al, 2000) as well as two amino acids that can vary leading to the identification of more than 250 MC variants (Puddick et al, 2014). The regulation and synthesis of MC, as well as its ecological role, are complex and not yet fully understood (Neilan et al, 2013;Omidi et al, 2017). Nodularin (NOD) is also a potent cyanobacterial hepatotoxin occurring in brackish waters (Sivonen et al, 1989;Kaebernick and Neilan, 2001).…”

Increased algicidal activity of Aeromonas veronii in response to Microcystis aeruginosa: interspecies crosstalk and secondary metabolites synergism

“…are key players in the global phenomenon of toxic cyanobacterial blooms which harm water quality in fresh water bodies by endangering humans, livestock, fish and even agriculture crops. Cases of human and livestock mortalities have been reported (see Neilan et al ., ; Paerl and Otten, ; Harke et al ., ; Huisman et al ., ; Omidi et al ., and references therein). Intensification of these blooms, worldwide, over the last two decades, is a matter of growing concern to water authorities and ecologists.…”

“…Cyanobacteria produce an array of secondary metabolites, some of which are toxic to eukaryotes, that is, microcystins, cylindrospermopsin, anatoxin, saxotoxin and others. The biological role(s) of these secondary metabolites in the aquatic ecosystem is, in most cases, not clear and debatable (El-Sheekh et al, 2010;Alexova et al, 2011;Dziallas and Grossart, 2011;Gan et al, 2012;Makower et al, 2015;Meissner et al, 2015;Harke et al, 2016) but their involvement in interspecies and intraspecies communication is emerging (Bar-Yosef et al, 2010;Zilliges et al, 2011;Kaplan et al, 2015;Pearson et al, 2016;Omidi et al, 2018). There is a growing body of evidence that the secondary metabolites are info-chemicals involved in the communication between the cyanobacteria and their partnersbacteria, phytoplankton species and fungus that share the ecological niche.…”