Understanding gold toxicity in aerobically-grown Escherichia coli

BACKGROUND: There Is an emerging field to put Into practice new strategies for developing molecules with antimicrobial properties. In this line, several metals and metalloids are currently being used for these purposes, although their cellular effect(s) or target(s) in a particular organism are still unknown. Here we aimed to investigate and analyze Au3+ toxicity through a combination of biochemical and molecular approaches. RESULTS: We found that Au3+ triggers a major oxidative unbalance in Escherichia coli, characterized by decreased intracellular thiol levels, increased superoxide concentration, as well as by an augmented production of the antioxidant enzymes superoxide dismutase and catalase. Because ROS production is, in some cases, associated with metal reduction and the concomitant generation of gold-containing nanostructures (AuNS), this possibility was evaluated in vivo and in vitro. CONCLUSIONS: Au3+ is toxic for E. coli because it triggers an unbalance of the bacterium's oxidative status. This was demonstrated by using oxidative stress dyes and antioxidant chemicals as well as gene reporters, RSH concentrations and AuNS generation.

Direct and derivative spectrophotometric determination of gold (iii) using 3,5-dimethoxy-4-hydroxybenzaldehyde benzoylhydrazone(dmbbh) in presence of micellar medium.

A simple and sensitive spectrophotometric method has been developed for the determination of Gold (III) using 3,5-Dimethoxy-4-hydroxy benzaldehyde benzoylhydrazone (DMBBH) in a neutral surfactant of Triton X-100(5%) (micellar medium). Gold (III) forms an wine red coloured water soluble complex with the reagent in acidic medium pH 5.0. The molar absorptivity and Sandell’s sensitivity of coloured species are 2.32 x 104 L.mol-1 cm-1 and 0.00862 mg/cm2 respectively. Beer’s law is obeyed in the range 0.4925-5.91 mg/ml of Au(III) at lmax at 380 nm. The developed derivative spectrophotometric method was employed for the determination of gold (III). This method has been satisfactorily applied for the determination of gold (III) in water samples and pharmaceutical samples.