Microcystin Production and Regulation under Nutrient Stress Conditions in Toxic Microcystis Strains

Abstract

Microcystin is a common and well-known cyanobacterial toxin whose intracellular role is still under investigation. Increasing knowledge on microcystin gene expression and regulation can contribute to the understanding of its putative cellular function. In this work, reverse transcription-quantitative PCR (RT-qPCR) was used to investigate the transcriptional response of the mcyD gene to nitrogen (nitrate and ammonium) and phosphorus limitation in two toxic Microcystis strains. The existence of a direct correlation between transcripts of mcyD and ntcA genes was also identified. In previous studies, NtcA (global nitrogen regulator) has been described as a potential component in the control of microcystin biosynthesis. This research showed that stress agents linked to nutrient deprivation could lead to a significant increase of microcystin production in both strains studied. The more toxic strain proved to be more resistant to nutrient limitation. The similar outcomes of mcyD regulation observed for all nutrients suggest that this response can be linked to oxidative stress of cells undergoing adverse growth conditions.

Predicting microcystin concentrations in lakes and reservoirs at a continental scale: A new framework for modelling an important health risk factor

“…Under stratified conditions and higher UV radiation, DOC is photocatalysed into superoxide and hydrogen peroxide, but MC‐producing cyanobacteria have several unique strategies to deal with these reactive oxygen species, including the formation of MC–protein complexes that prevent proteolytic degradation within the cyanobacterial cell (Paerl & Otten, ). Thus, MCs provide a competitive advantage to toxic cyanobacteria via their protective role under oxidative stress‬ (Pimentel & Giani, ). We suggest that at higher MC limits, where algal concentrations are much higher, UV penetration into the water column is greatly limited and this effect is much diminished.…”

“…Thus, MCs provide a competitive advantage to toxic cyanobacteria via their protective role under oxidative stress (Pimentel & Giani, 2014).…”

“…We suggest that at higher MC limits, where algal concentrations are much higher, UV penetration into the water column is greatly limited and this effect is much diminished. At this extreme, MC production may also increase several fold due to quorum sensing and stress from nutrient limitation (Pereira & Giani, 2014;Pimentel & Giani, 2014;Van de Waal et al, 2009;Wood et al, 2011).…”

Influence of temperature, mixing, and addition of microcystin-LR on microcystin gene expression inMicrocystis aeruginosa

“…Unfortunately, toxic and nontoxic genotypes cannot be distinguished by means of microscopy (Komárek, 1991). Based on the knowledge about the genetic basis of microcystin synthesis, PCR-based assays have been developed to distinguish toxic from nontoxic strains at the molecular level (Al-Tebrineh et al, 2012;Fortin et al, 2010;Hautala et al, 2013;Hisbergues, Christiansen, Rouhiainen, Sivonen, & Borner, 2003;Kurmayer & Kutzenberger, 2003;Ostermaier & Kurmayer, 2010;Pimentel & Giani, 2014;Rantala et al, 2006). The detection and quantification of toxicity genes are of special interest because the direct detection of microcystin has certain limitations and drawbacks.…”

Microcystin-degrading bacteria affect mcyD expression and microcystin synthesis in Microcystis spp.

“…For example, high light intensity resulted in an increase of transcription of mcyB and mcyD (Kaebernick et al, 2000). Nitrogen (nitrate and ammonium) and phosphorus limitation were also found to up-regulate the transcription of mcyD (Pimentel and Giani, 2014). Iron deficient conditions resulted in an increase of mcyD and mcyH transcription, correlating with an increase in microcystin-leucine-arginine (MC-LR) levels (Sevilla et al, 2008;Alexova et al, 2011).…”