Cadmium-resistant mutant of Bacillus subtilis 168 with reduced cadmium transport

Abstract

Cd21 and Mn21 accumulation was studied with wild-type Bacillus subtilis 168 and a Cd2+-resistant mutant. After 5 min of incubation in the presence of 0.1 ,uM '09Cd2+ or 54Mn2+, both strains accumnulated comparable amounts of 54Mn2+, while the sensitive cells accumulated three times more 109Cd2+ than the Cd2+-resistant cells did. Both 54Mn2+ and 109Cd2+ uptake, which apparently occur by the same transport system, demonstrated cation specificity; 20 ,uM Mn2+ or Cd2+ (but not Zn2+) inhibited the uptake of 0.1 p.M '09Cd2+ or 54Mn2+. 54Mn2+ and '09Cd2+ uptake was thergy dependent and temperature sensitive, but '09Cd2+ uptake in the Cd2+-resistant strain was only partially inhibited by an uncoupler or by a decreast in temperature. 109Cd2+ uptake in the sensitive strain followed MichaelisOIenten kinetics with a Km of 1.8 ,uM Cd2+ and a V..x of 1.5 ,imol/min. g (dry weight); 109Cd2+ uptake in the Cd2+-resistant strain was not saturable. The apparent Km value for the saturable component of "09Cd2+ uptake by the Cd2-resistant strain was very similar to that of the sensitive strain, but the Vmax was 25 times lower than the V., for the sensitive strain. The Km and Vi.. for 54Mn2+ uptake by both strains were very similar. Cd2+ inhibition of M4Mn2+ uptake had an apparent Ki of 3.4 and 21.5 ,uM Cd2+ for the sensitive and Cd2-resistant strains, respectively. Mn2+ had an apparent Ki of 1.2 ,uM Mn2+ for Inhibition of '09Cd2+ uptake by the sensitive strain, but the Cd2+-resistant strain had no defined Ki value for inhibition of Cd2+ uptake by Mn2+. Cd2+ is toxic to bacteria (13). A mechanism of resistance to Cd2" has been studied in Staphylococcus aureus. S. aureus is normally sensitive to concentrations of Cd2" above about 2 ,uM, but if a plasmid which confers resistance to Cd2+ is introduced into the organism, it is resistant to up to 200 ,uM Cd2+ (14). The plasmid codes for a Cd2+ efflux (antiporter) transport system which rapidly transports Cd2+ out of the cells (9, 11). Recently, a Cd2+-resistant mutant of Bacillus subtilis 168 was isolated (10). Both the parental and mutant strains are plasmidless. The mutant strain was obtained by successive transfers of the parental strain into medium containing up to 90 ,.M Cd2+. Under steady-state conditions, the Cd2+sensitive parental strain accumulated 10 times the level of Cd2+ that the Cd2+-resistant mutant strain accumulated. This Cd2+-resistant strain appears to be the first chromosomally determined Cd2+-resistant mnutant isolated. Cd2+ resistance in this strain is expressed constitutively (10).

Cadmium sequestration in cells of two stains ofAlcaligenes eutrophus

“…and its non-adapted parent. These findings obtained with the genus Alcaligenes disaccord with the results obtained with strains of Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus subtills [11][12][13][14][15]. In these three species, the sensitive strains always accumulated more cadmium than the insensitive.…”

Cadmium-induced loss of surface polyphosphate in Acinetobacter lwoffi

“…At 30°C, Cd 2÷ accumulation occurs in A. lwoffi within 2 min and is sensitive not only to low temperature (4°C) but also to the addition of carbonylcyanide m-chlorophenyl-hydrazone (CCCP), an uncoupling agent that abolishes proton symport. Thus, Cd 2+ is accumulated by active transport in A. lwoffi, as in other bacteria examined [7][8][9][10][11]. Fig.…”

“…Growth was not inhibited until concentrations of Cd 2+ 50/~M. This is 10-20 times the concentration of Cd 2+ that sensitive bacteria tolerate in broth [7]. In synthetic Lac MM, growth is inhibited at Cd 2÷ concentrations above 0.5/~M.…”

“…If Pn participates directly in sugar transport by controlling the energy charge [1], then one would expect a similar mechanism for other molecules that enter the cell by active transport. Cd 2+ uptake in several bacteria occurs by means of either the Mn 2+ [7][8][9][10] or Zn 2+ [11] * To whom correspondence should be addressed.…”

Metal accumulation by heterotrophic marine bacterioplankton

“…The uptake of Cd by marine bacteria has previously been investigated (Iyer et al 2005), and it has been shown that its accumulation is energy dependent and that it occurs through the Mn transport system in at least some species (Laddaga et al 1985). Phytoplankton and bacteria transport Cd into their cells, where it sometimes replaces Zn when this metal is available in limiting amounts (Price and Morel 1990).…”