Abstract:The hepatotoxin microcystin (MCYST) is produced by a variety of freshwater cyanobacterial species, including Microcystis aeruginosa. Interestingly, MCYST-producing M. aeruginosa strains have been shown to outcompete their nontoxic counterparts under iron-limiting conditions. However, the reasons for this are unclear. Here we examined the proteomic response of M. aeruginosa PCC 7806 continuous cultures under different iron and growth regimes. Iron limitation was correlated with a global reduction in levels of p… Show more
“…Under oxidative stress, more MCs are released to the surrounding environment and therefore might play a role as a signal molecule to synchronize the cell responses to the stress-inducing agents. Increased intracellular MC concentration in response to oxidative stress conditions such as iron limitation support the hypothesis of MCs involvement in protection against oxidative stress, while the enhancement in extracellular MCs suggests the possible role of MCs as a signal molecule to make a better environmental adaptation (Yeung et al 2016).…”
Section: Future Outlook and Concluding Remarkmentioning
confidence: 58%
“…A recent proteomic study using continuous cultures of M. aeruginosa PCC 7806 showed that under iron depletion physiological changes such as reduction in chlorophyll a content besides enhancement in MC production. Increased intracellular and extracellular MCs in continuous culture of M. aeruginosa PCC 7806 under iron depletion provided more evidence of the assistance role of MCs in the better fitness of Microcystis under oxidative stress conditions (Yeung et al 2016). In addition, mcy gene transcripts were enhanced under oxidative stress in various quantities i.e.…”
Section: Protection Against Oxidative Stressmentioning
confidence: 99%
“…• Increased extracellular MCs (Yeung et al 2016) Similarity between the sequence of the mcy gene cluster…”
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
“…Under oxidative stress, more MCs are released to the surrounding environment and therefore might play a role as a signal molecule to synchronize the cell responses to the stress-inducing agents. Increased intracellular MC concentration in response to oxidative stress conditions such as iron limitation support the hypothesis of MCs involvement in protection against oxidative stress, while the enhancement in extracellular MCs suggests the possible role of MCs as a signal molecule to make a better environmental adaptation (Yeung et al 2016).…”
Section: Future Outlook and Concluding Remarkmentioning
confidence: 58%
“…A recent proteomic study using continuous cultures of M. aeruginosa PCC 7806 showed that under iron depletion physiological changes such as reduction in chlorophyll a content besides enhancement in MC production. Increased intracellular and extracellular MCs in continuous culture of M. aeruginosa PCC 7806 under iron depletion provided more evidence of the assistance role of MCs in the better fitness of Microcystis under oxidative stress conditions (Yeung et al 2016). In addition, mcy gene transcripts were enhanced under oxidative stress in various quantities i.e.…”
Section: Protection Against Oxidative Stressmentioning
confidence: 99%
“…• Increased extracellular MCs (Yeung et al 2016) Similarity between the sequence of the mcy gene cluster…”
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
“…Recent research raises the possibility that microcystins may play a role in enhancing the ability of surviving oxidative stress [1,31]. The increased production of intracellular MC under conditions of stress [32] allowed MC-producing strains to cope better with oxidative stress over non-toxic strain [21,30,33]. However, other findings show opposite results: The nontoxic M. aeruginosa PCC7806 mutant was favored over its toxic wild type when exposed to prolonged oxidative stress caused by hydrogen peroxide [34].…”
While the intracellular function of many toxic and bioactive cyanobacterial metabolites is not yet known, microcystins have been suggested to have a protective role in the cyanobacterial metabolism, giving advantage to toxic over nontoxic strains under stress conditions. The zooplankton grazer Daphnia reduce cyanobacterial dominance until a certain density, which may be supported by Daphnia exudates, affecting the cyanobacterial physiological state and metabolites’ production. Therefore, we hypothesized that D. magna spent medium will impact the production of cyanobacterial bioactive metabolites and affect cyanobacterial photosynthetic activity in the nontoxic, but not the toxic strain. Microcystin (MC-LR and des-MC-LR) producing M. aeruginosa PCC7806 and its non-microcystin producing mutant were exposed to spent media of different D. magna densities and culture durations. D. magna spent medium of the highest density (200/L) cultivated for the shortest time (24 h) provoked the strongest effect. D.magna spent medium negatively impacted the photosynthetic activity of M. aeruginosa PCC7806, as well as the dynamics of intracellular and extracellular cyanobacterial metabolites, while its mutant was unaffected. In the presence of Daphnia medium, microcystin does not appear to have a protective role for the strain. On the contrary, extracellular cyanopeptolin A increased in M. aeruginosa PCC7806 although the potential anti-grazing role of this compound would require further studies.
“…Consequently, it is deduced that the majority of MC–LR was kept inside the cells during our experiment and little MC–LR was released into external environment. Several studies have also reported that maximum MC concentrations were not recorded until the end of the growth cycle or during bloom collapse [ 73 ]. Therefore, iron addition could actually increase the intracellular toxin production but may not raise the extracellular MC–LR concentration during the blooms.…”
Blooms of harmful cyanobacteria have been observed in various water bodies across the world and some of them can produce intracellular toxins, such as microcystins (MCs), which negatively impact aquatic organisms and human health. Iron participates significantly in cyanobacterial photosynthesis and is proposed to be linked to MC production. Here, the cyanobacteria Microcystis aeruginosa was cultivated under different iron regimes to investigate the relationship between photosynthetic capacity and MC production. The results showed that iron addition increased cell density, cellular protein concentration and the Chl-a (chlorophyll-a) content. Similarly, it can also up–regulate photosynthetic capacity and promote MC–leucine–arginine (MC–LR) production, but not in a dose–dependent manner. Moreover, a significant positive correlation between photosynthetic capacity and MC production was observed, and electron transport parameters were the most important parameters contributing to the variation of intracellular MC–LR concentration revealed by Generalized Additive Model analysis. As the electron transport chain was affected by iron variation, adenosine triphosphate production was inhibited, leading to the alteration of MC synthetase gene expression. Therefore, it is demonstrated that MC production greatly relies on redox status and energy metabolism of photosynthesis in M. aeruginosa. In consequence, more attention should be paid to the involvement of photosynthesis in the regulation of MC production by iron variation in the future.
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