Factors regulating methyl mercury uptake in a cyanobacterium.
The simultaneous addition of dithiothreitol (DTT), mercaptoethanol, and glutathione (30 microM each) and CH3Hg+ to Nostoc calcicola cells reduced CH3Hg+ uptake in the order GSH > DTT > mercaptoethanol. However, the preexposure of cyanobacterial cells to similar thiols resulted in different pattern of CH3Hg+ uptake in the sequence: GSH > mercaptoethanol > DTT. Light-grown cyanobacterial cells demonstrated a faster initial uptake of CH3Hg+ (rate 0.619 mumol CH3Hg+ mg-1 protein min-1, 10 min) with a biphasic pattern saturating at 30 min (bioconcentration factor = 2.7 x 10(3)). 3-(3,4-Dichlorophenyl)-1,1'-dimethyl urea (30 microM) reduced the uptake rate by 5% with a corresponding 33% reduction in CH3Hg+ accumulation. Dark exposure (24 hr) of cells reduced the CH3Hg+ uptake rate (22.3%) accompanied by a considerable decline in the bioconcentration factor (1.4 x 10(3)). Of the four permeabilizers used, p-chloromercuribenzoate (1 microM) proved most effective in altering the CH3Hg+ uptake kinetics while dimethyl sulfoxide (5%) and cetyl trimethylammonium bromide (1%) lowered the bioconcentration factor to 2.2 x 10(3) and 1.2 x 10(3), respectively. After toluene exposure, however, the cells revealed no sign of CH3Hg+ uptake. The data have been discussed in light of the role(s) of thiols, photoautotrophy, and membrane integrity in regulating the cellular influx of CH3Hg+.
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Algal Research Laboratory, Banaras Hindu University, Varanasi, India.
Srivastava
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SC
Singh
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D000458:Cyanobacteria / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D008767:Methylmercury Compounds / Q000378:metabolism*; D014176:Protein Biosynthesis; D012997:Solvents / Q000494:pharmacology; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology
D008767:Methylmercury Compounds; D012997:Solvents; D013438:Sulfhydryl Compounds; D014475:Uncoupling Agents