Abstract
HCH factories, and the waste dumpsites associated to its production, have become a global environmental concern, and their runoff could pollute ground and surface waters with high levels of the pollutant. In this study, the influence of lindane (γ-HCH) on microcystin production has been investigated in Microcystis aeruginosa PCC7806. This toxic cyanobacterium is highly tolerant to γ-lindane (20 mg/L), and produces more toxin (microcystin) in the presence of the pollutant. Microcystis degrades γ-lindane and presence of γ-lindane induces genes involved in its own degradation (nirA). RT-PCRsq has been used to monitor changes in levels of transcripts encoded by the mcy operon (mcyD, mcyH and mcyJ), responsible for the microcystin synthesis machinery, as well as other genes involved in its transcriptional regulation, such as ntcA and fur family members. The presence of lindane in the culture media induces mcyD expression, as well as ntcA gene transcription, while other genes, such as mcyH, (putative ABC transporter), are downregulated. The amount of microcystin found in the cells and the culture media is higher when M. aeruginosa is treated with γ-lindane than in control cells. The results suggest that in a lindane polluted environment, Microcystis toxic strains may enhance their microcystin synthesis.
Highlights
Cyanobacteria are organisms with an outstanding capacity to adapt to a wide range of environments and survive in extreme or highly degraded environments
The toxic Microcystis aeruginosa PCC7806 exhibits a considerable tolerance to lindane, surviving and growing up to 20 mg/L (Figure 1), whereas the growth of a field isolated Microcystis aeruginosa strain (Kützing) Lemmermann (MaD7) was completely inhibited at 5 mg/L [11]
Lindane was added from a stock solution in ethanol
Summary
Cyanobacteria are organisms with an outstanding capacity to adapt to a wide range of environments and survive in extreme or highly degraded environments. Their metabolic plasticity includes the synthesis of a broad variety of secondary metabolites, some of them potentially toxic for eukaryotic organisms, the so-called cyanotoxins [1,2]. Microcystis aeruginosa is a freshwater cyanobacterium responsible for many toxic blooms, producing microcystin. Sometimes it is naturally occurring in the tidal fresh estuaries and low salinity coastal areas, and there is an alarming increase of blooms in such mesohaline estuaries [3].
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