A REASSESSMENT OF THE RANGE OF C-TYPE CYTOCHROMES SYNTHESIZED BY ESCHERICHIA-COLI K-12

Five different c-type cytochromes have been detected during anaerobic growth of various Escherichia coli strains in different media. None of these cytochromes was detectable in aerobically-grown cultures. Only a single, 43 kDa cytochrome was synthesized in response to the presenc e of trimethylamine-N-oxide: synthesis of this cytochrome was unaffect ed by the presence of nitrate or nitrite, was repressed by oxygen, but was dependent upon a functional tor operon located at minute 22 (coor dinate 1070 kb) on the E. coli chromosome. The other four cytochromes, masses 16, 18, 24 and 50 kDa, were induced by nitrite coordinately wi th formate-dependent nitrite reductase activity, but repressed by oxyg en and nitrate. As only the 18 kDa and 50 kDa cytochromes are encoded by the nrf operon located at minute 92 (coordinate 4366 kb), there mus t be other loci, possibly essential for formate-dependent nitrite redu ction, encoding the 16 kDa and 24 kDa cytochromes. No other c-type cyt ochrome was detected under any growth condition tested.