FACTORS REGULATING METHYL MERCURY UPTAKE IN A CYANOBACTERIUM

The simultaneous addition of dithiothreitol (DTT), mercaptoethanol, an d glutathione (30 mu M each) and CH3Hg+ to Nostoc calcicola cells redu ced CH3Hg+ uptake in the order GSH > DTT > mercaptoethanol. However, t he preexposure of cyanobacterial cells to similar thiols resulted in d ifferent pattern of CH3Hg+ uptake in the sequence: GSH > mercaptoethan ol > DTT. Light-grown cyanobacterial cells demonstrated a faster initi al uptake of CH3Hg+ (rate 0.619 mu mol 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 mu M) reduced the uptake rate by 5% with a corresponding 33% reduction in CH3Hg+ accumulation. Dark exposure (24 hr) of cells reduced the CH 3Hg+ 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 mu M) proved most effective in altering t he CH3Hg+ uptake kinetics while dimethyl sulfoxide (5%) and cetyl trim ethylammoniun 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 disc ussed in light of the role(s) of thiols, photoautotrophy, and membrane integrity in regulating the cellular influx of CH3Hg+. (C) 1995 Acade mic Press, Inc.