Cysteine metabolism-related genes and bacterial resistance to potassium tellurite

Abstract

Tellurite exerts a deleterious effect on a number of small molecules containing sulfur moieties that have a recognized role in cellular oxidative stress. Because cysteine is involved in the biosynthesis of glutathione and other sulfur-containing compounds, we investigated the expression of Geobacillus stearothermophilus V cysteine-related genes cobA, cysK, and iscS and Escherichia coli cysteine regulon genes under conditions that included the addition of K2TeO3 to the culture medium. Results showed that cell tolerance to tellurite correlates with the expression level of the cysteine metabolic genes and that these genes are up-regulated when tellurite is present in the growth medium.

FIG. 1.

Growth inhibition zones of E. coli cells expressing G. stearothermophilus V cobA, cysK, and iscS genes cloned in pBR322 when exposed to the following toxic substances: paraquat (A), diamide (B), hydrogen peroxide (C), and potassium tellurite (D). Cells were grown overnight in plates of LB-ampicillin at 37°C. Error bars represent standard deviations (n = 8). See Materials and Methods for details.

FIG. 2.

Determination of β-galactosidase activity in E. coli ADA110 (A) and ADA310 (B) in the presence of potassium tellurite. Cells harboring pSKcobA (▵), pSKcysK (○), pSKiscS (⋄), or the control plasmid pBluescript SK⁻ (▪) were grown at 37°C in LB medium until an OD₆₀₀ of about 0.6 (time zero), when tellurite was amended at 0.5 μg/ml. Control cells were grown in the absence of potassium tellurite (□). Error bars represent standard deviations (n = 9).

FIG. 3.

Expression of G. stearothermophilus V genes in LB medium containing potassium tellurite (50 μg/ml). Cells were grown at 65°C for 24 h as described in Materials and Methods. Values are the means of two independent trials.

FIG. 4.

Growth inhibition zones of E. coli defective in the indicated cysteine metabolism-related genes. Cells were grown in LB medium in the presence of paraquat (A), diamide (B), hydrogen peroxide (C), and potassium tellurite (D). Results for the parental, isogenic, wild-type BW25113 strain are shown to the right of each histogram. Error bars represent standard deviations (n = 6).

FIG. 5.

Expression of E. coli cys genes in medium containing potassium tellurite. Cells were inoculated in LB medium containing 0.5 μg/ml of potassium tellurite and cultivated at 37°C with shaking for 24 h. Values are the means of two independent trials.