nrdD and nrdG genes are essential for strict anaerobic growth of Escherichia coli.

In Escherichia coli ribonucleotide reduction is catalyzed by two separate enzymes during aerobic and anaerobic growth. The aerobic enzyme is coded by the nrdAB genes, the anaerobic enzyme by nrdDG. We now show that knock-out mutants of either nrdD or nrdG cannot grow during strict anaerobiosis, achieved by inclusion of sodium sulfide in the medium. Interestingly, these mutants grow well under microaerophilic conditions by overproducing the aerobic enzyme. Under such conditions wild-type bacteria turn off nrdAB and switch on nrdDG.