Expression of Cytochrome Oxidases in Bacillus cereus: Effects of Oxygen Tension and Carbon Source

SUMMARY: The expression of three putative terminal oxidases (cytochromes aa 3, o and d) of Bacillus cereus was studied in response to oxygen tension and the nature of the carbon source used for growth. High levels of cytochromes b and o were expressed irrespective of culture conditions. Oxygen deprivation caused a large drop in the levels of cytochromes c and aa 3. Cytochrome d appeared at low oxygen tensions, in anaerobic cultures and during slow aerobic growth on poorly utilized carbon sources (casein hydrolysate). No cytochrome d was detected during fast aerobic growth in fermentable (sucrose-containing) media or when NaNO3 was added to anaerobic cultures. Cytochromes aa 3, o and d were reduced by physiological substrates (NADH and succinate) and by ascorbate plus tetramethyl-p-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 aa 3. Thus, the involvement of cytochromes o and d in the cyanide-resistant respiration of Bacillus cereus is suggested.