UV-B Exposure Affects the Biosynthesis of Microcystin in Toxic Microcystis aeruginosa Cells and Its Degradation in the Extracellular Space.

Zhen Yang,Fanxiang Kong

doi:10.3390/toxins7104238

Zhen Yang, Fanxiang Kong

Open Access

https://doi.org/10.3390/toxins7104238

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Abstract

Microcystins (MCs) are cyclic hepatotoxic heptapeptides produced by cyanobacteria that can be toxic to aquatic and terrestrial organisms. MC synthesis and degradation are thought to be influenced by several different physical and environmental parameters. In this study, the effects of different intensities of UV-B radiation on MC biosynthesis in Microcystis cells and on its extracellular degradation were investigated by mRNA analysis and degradation experiments. Exposure to UV-B at intensities of 1.02 and 1.45 W/m2 not only remarkably inhibited the growth of Microcystis, but also led to a decrease in the MC concentration. In addition, mcyD transcription was decreased under the same UV-B intensities. These results demonstrated that the effects of UV-B exposure on the biosynthesis of MCs in Microcystis cells could be attributed to the regulation of mcy gene transcription. Moreover, the MC concentration was decreased significantly after exposure to different intensities of UV-B radiation. Of the three MC variants (MC-LR, -RR and -YR, L, R and Y are abbreviations of leucine, arginine and tyrosine), MC-LR and MC-YR were sensitive to UV-B radiation, whereas MC-RR was not. In summary, our results showed that UV-B radiation had a negative effect on MC production in Microcystis cells and MC persistence in the extracellular space.

Highlights

Blooms of the cyanobacterium Microcystis sp. in eutrophic lakes, ponds and reservoirs have become severe environmental problems in many countries
Radiation intensity and MC concentration. We reported that both intracellular and extracellular MC levels decreased markedly when MC-producing Microcystis was exposed to UV-B radiation
The synthesis of both mycosporine-like amino acids (MAAs), which absorb UV radiation, and carotene, which counteracts reactive oxidants, may allow Microcystis to cope with low-intensity UV-B radiation, damage caused by high-intensity UV-B radiation cannot be discounted [30]

Summary

Introduction

Blooms of the cyanobacterium Microcystis sp. in eutrophic lakes, ponds and reservoirs have become severe environmental problems in many countries. It has been reported that the MC production of toxigenic strains is regulated by environmental factors, such as temperature [8], light intensity [9,10], nutrient concentrations or sources [11,12,13] and pH [14]. Some of these factors are involved in enhancing or repressing the expression of the mcy gene, leading to an increase or decrease in MC production, respectively. It was shown that stress conditions caused by nutrient deprivation clearly increased mcyD transcription and MC production [15]

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