Figure 6
cAMP in excess inhibits cytochromes cbb3 and bd.
(A) Effect of cAMP on susceptibility of indicated strains to 5 mM nitrite on LB plates. Cytochrome bd confers S. oneidensis resistance to nitrite. ∆cpdA/cpdA, ∆cpdA∆crp/cpdA and ∆cpdA∆crp/cyd represent indicated mutants expressing cpdA or cyd by IPTG at levels sufficiently high for successful complementation as described in the text or previous publications. (B) Effect of cAMP on cytochrome cbb3 activity of indicated strains on LB plates by the Nadi assay. The method is based on the rapid formation of indophenol blue from colorless a-naphthol catalyzed by cytochrome c oxidase, using N′,N′-dimethyl-p-phenylenediamine monohydrochloride as an exogenous electron donor. Photos were taken at indicated times after the reaction started. The wild-type and ΔccoN strains serve as positive and negative controls. (C) Growth of ∆cpdA∆cyd in LB. (D) Growth of ∆cpdA∆cco in LB. (E) Impacts of cAMP on expression of cyd and cco operons. Activities of the cyd and cco operon promoters from mid-log phase samples were assayed by a lacZ-reporter system used previously17. ∆cpdA/cpdA and ∆cpdA∆crp/cpdA represent indicated mutants expressing cpdA by IPTG at levels sufficiently high for successful complementation as described in the text or previous publications. All experiments were performed at least three times with standard deviations presented as error bars or similar results were obtained.
