Factors regulating methyl mercury uptake in a cyanobacterium

Area of Science:

• Environmental Toxicology
• Microbiology
• Biochemistry

Background:

• Methylmercury (CH3Hg+) is a potent neurotoxin that bioaccumulates in aquatic ecosystems.
• Cyanobacteria, like Nostoc calcicola, are primary producers and can be exposed to environmental contaminants.
• Cellular uptake mechanisms for heavy metals are influenced by various environmental factors and cellular components.

Purpose of the Study:

• To investigate the role of thiols (dithiothreitol, mercaptoethanol, glutathione) in regulating CH3Hg+ uptake by Nostoc calcicola.
• To determine the impact of light, dark exposure, and membrane integrity on CH3Hg+ accumulation.
• To elucidate the kinetics and bioconcentration factors of CH3Hg+ uptake under different conditions.

Main Methods:

• Exposure of Nostoc calcicola cells to CH3Hg+ with simultaneous or pre-exposure to various thiols.
• Treatment with inhibitors (3-(3,4-Dichlorophenyl)-1,1'-dimethyl urea) and permeabilizers (p-chloromercuribenzoate, dimethyl sulfoxide, cetyl trimethylammonium bromide).
• Assessment of CH3Hg+ uptake rates, accumulation, and bioconcentration factors under light and dark conditions, and after toluene exposure.

Main Results:

• Simultaneous addition of thiols reduced CH3Hg+ uptake, with glutathione (GSH) showing the greatest reduction.
• Pre-exposure to thiols altered uptake patterns, with GSH > mercaptoethanol > dithiothreitol (DTT).
• Light-grown cells exhibited faster initial CH3Hg+ uptake; dark exposure and certain permeabilizers reduced uptake and bioconcentration factors.

Conclusions:

• Thiols, photoautotrophy, and membrane integrity are critical regulators of CH3Hg+ influx in Nostoc calcicola.
• The differential effects of thiols depend on whether they are added simultaneously or used for pre-exposure.
• Understanding these factors is crucial for assessing the environmental risk of CH3Hg+ in aquatic microbial communities.