effect of chelating agents and respiratory inhibitors on regulation of the cada gene in escherichia coli the cada gene that encodes lysine decarboxylase in escherichia coli is induced by low ph and during anaerobic growth by the substrate lysine we used operon fusions of cada to lacz to investigate the effects of aeration on cada regulation when an insertion mutation in osmz hns was introduced a cadalacz fusion was derepressed in the presence of air to approximately the same level as seen during anaerobic growth however the phdependent regulation of cada was not affected by osmz introduction of mutations in rpos fur or fnr had no significant effect on cada expression however defects in arcb or arca largely abolished expression of cada during anaerobic growth nonetheless strains defective in both arcb and osmz showed the same high cadalac expression in air as seen in the single osmz derivatives blocking the respiratory chain with mutations or chemical inhibitors also caused derepression of a cadalacz fusion in air while agents affecting the proton gradient had no effect derepression of cada in air was also mediated by several chelating agents in particular by methoxyindole carboxylic acid addition of fe2 overcame this effect chelating agents also abolished the expression during aerobic growth of several genes known to be under arcab control and which are normally repressed during anaerobic growth but induced in the presence of air this implies that the effect of chelating agents on cada expression is mediated via the arcab regulatory system