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
The escalating occurrence of toxic cyanobacterial blooms worldwide is a matter of concern. Global warming and eutrophication play a major role in the regularity of cyanobacterial blooms, which has noticeably shifted towards the predomination of toxic populations. Therefore, understanding the effects of cyanobacterial toxins in aquatic ecosystems and their advantages to the producers are of growing interest. In this paper, the current literature is critically reviewed to provide further insights into the ecological contribution of cyanotoxins in the variation of the lake community diversity and structure through interspecies interplay. The most commonly detected and studied cyanobacterial toxins, namely the microcystins, anatoxins, saxitoxins, cylindrospermopsins and β-N-methylamino-L-alanine, and their ecotoxicity on various trophic levels are discussed. This work addresses the environmental characterization of pure toxins, toxin-containing crude extracts and filtrates of single and mixed cultures in interspecies interactions by inducing different physiological and metabolic responses. More data on these interactions under natural conditions and laboratory-based studies using direct co-cultivation approaches will provide more substantial information on the consequences of cyanotoxins in the natural ecosystem. This review is beneficial for understanding cyanotoxin-mediated interspecies interactions, developing bloom mitigation technologies and robustly assessing the hazards posed by toxin-producing cyanobacteria to humans and other organisms.
Although microcystins (MCs) are the most commonly studied cyanotoxins, their significance to the producing organisms remains unclear. MCs are known as endotoxins, but they can be found in the surrounding environment due to cell lysis, designated as extracellular MCs. In the present study, the interactions between MC producing and the non-producing strains of
Microcystis aeruginosa
, PCC 7806 and PCC 7005, respectively, and a green alga,
Desmodesmus subspicatus
, were studied to better understand the probable ecological importance of MCs at the collapse phase of cyanobacterial blooms. We applied a dialysis co-cultivation system where
M. aeruginosa
was grown inside dialysis tubing for one month. Then,
D. subspicatus
was added to the culture system on the outside of the membrane. Consequently, the growth of
D. subspicatus
and MC contents were measured over a 14-day co-exposure period. The results showed that
Microcystis
negatively affected the green alga as the growth of
D. subspicatus
was significantly inhibited in co-cultivation with both the MC-producing and -deficient strains. However, the inhibitory effect of the MC-producing strain was greater and observed earlier compared to the MC-deficient strain. Thus, MCs might be considered as an assistant factor that, in combination with other secondary metabolites of
Microcystis
, reinforce the ability to outcompete co-existing species.
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