SUMMARY: The expression of three putative terminal oxidases (cytochromes , and ) of was studied in response to oxygen tension and the nature of the carbon source used for growth. High levels of cytochromes and were expressed irrespective of culture conditions. Oxygen deprivation caused a large drop in the levels of cytochromes and . Cytochrome appeared at low oxygen tensions, in anaerobic cultures and during slow aerobic growth on poorly utilized carbon sources (casein hydrolysate). No cytochrome was detected during fast aerobic growth in fermentable (sucrose-containing) media or when NaNO was added to anaerobic cultures. Cytochromes , and were reduced by physiological substrates (NADH and succinate) and by ascorbate plus tetramethyl--phenylenediamine (TMPD). Oxidase activity using ascorbate-TMPD as electron donor was significantly more resistant to cyanide inhibition in cells containing none or trace amounts of cytochrome . Thus, the involvement of cytochromes and in the cyanide-resistant respiration of is suggested.


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