Thesis

Cyanide resistant respiration in Bacillus cereus

Cyanide exerts its toxic effects by inhibiting cellular respiration, specifically by inhibiting cytochrome oxidase. In many bacteria, algae, protozoa and plants cyanide resistance has been demonstrated and is usually associated with an alternate electron transport pathway. A strain of Bacillus cereus was isolated using an elective culture containing cyanide. In 1 mM cyanide, the population growth rate was one-third that of control cells grown in the same medium lacking cyanide. The rate of oxygen consumption was approximately 50% of controls. The addition of 2 mM cyanide to respiring control cells resulted in virtually complete inhibition of oxygen uptake, but only 40% inhibition in cyanide-grown cells. No qualitative or quantitative differences in the cytochromes of the electron transport systems were noted between control and cyanide-grown cells in reduced-minus oxidixed difference spectra. In CO-difference spectra, control cells had one absorption peak at 430 nm. CO difference spectra of cyanide-grown cells lacked this peak, but showed peaks at 500 and 550 nm. The absence of the peak at 430 nm in cyanide-grown cells suggests either that alternate oxidases are produced or that cyanide alters the cytochrome a. (See more in text.)

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