OxyFile #225

Mechanism of chromium(VI) toxicity in Escherichia coli: 
is hydrogen peroxide essential in Cr(VI) toxicity?

Author:  Itoh M; Nakamura M; Suzuki T; Kawai K; Horitsu H; 
         Takamizawa K

Source:  J Biochem (Tokyo) 1995 Apr; 117(4):780-6


To investigate the role of hydrogen peroxide in Cr(VI) 
toxicity in vivo toward bacterial cells, we examined the 
effect of Cr(VI), hydrogen peroxide, sodium azide, and 
mannitol on the viability of Escherichia coli. Bacterial 
cells were incubated for 1 h with shaking in the presence 
of Cr(VI), hydrogen peroxide, sodium azide as catalase 
inhibitor, and/or mannitol as radical scavenger. The colony-
forming ability and double-strand DNA degradation were examined. 
The viability assays revealed that Cr(VI) toxicity depended 
on hydroxyl radicals generated in the reaction involving 
hydrogen peroxide and chromium. Moreover, incubation of 
E. coli cells with 10 mM Cr(VI) and 3 mM hydrogen peroxide 
caused the degradation of double-strand DNA in vivo, which 
was suppressed by the addition of mannitol. These results 
indicated that hydroxyl radicals generated in the incubation 
degraded DNA of E. coli cells, resulting in cell death. 
In the absence of added hydrogen peroxide, the intracellular 
concentration of hydrogen peroxide in E. coli was low (below 
1 microM). A catalase-defective strain incubated in the 
absence of added hydrogen peroxide remained fully viable 
after 1 h but showed decreased viability after prolonged 
incubation (4-8 h). The addition of mannitol suppressed 
this decrease, suggesting that hydroxyl radicals may be 
involved in the expression of Cr(VI) toxicity even without 
added hydrogen peroxide.