THE TEMPERATURE-SENSITIVE GROWTH AND SURVIVAL PHENOTYPES OF ESCHERICHIA-COLI CYDDC AND CYDAB STRAINS ARE DUE TO DEFICIENCIES IN CYTOCHROME BD AND ARE CORRECTED BY EXOGENOUS CATALASE AND REDUCING AGENTS

The cydDC operon of Escherichia coli encodes an ATP-dependent transpor ter of unknown function that is required for cytochrome bd synthesis, Strains containing defects in either the cydD or cydC gene also demons trate hypersensitivity to growth at high temperatures and the inabilit y to exit the stationary phase at 37 degrees C, We wished to determine what is responsible for these hypersensitive phenotypes and whether t hey are due to a lack of the CydDC proteins or a defect of the cytochr ome bd encoded by the cydAB genes. Using both K-12- and B-type strains of E. coli, we have compared the phenotypes of isogenic cydAB mutants and cydC mutants. In both K-12- and B-type backgrounds, the hypersens itive phenotypes are due to defects of cytochrome bd activity and not defects of the cynDC genes. We also found that the temperature-sensiti ve growth phenotypes can be suppressed by exogenous reducing agents, s uch as glutathione and cysteine, Strikingly, even the enzymes catalase and superoxide dismutase, when added exogenously, can correct the tem perature-sensitive and stationary phase arrest phenotypes. We propose that the temperature sensitive growth phenotypes are due to a buildup of diffusible oxygen radicals brought on by the absence of cytochrome bd.