Involvement of the cbb 3 -Type Terminal Oxidase in Growth Competition of Bacteria, Biofilm Formation, and in Switching between Denitrification and Aerobic Respiration.

Paracoccus denitrificanshas a branched electron transport chain with three terminal oxidases transferring electrons to molecular oxygen, namelyaa(3)-type andcbb(3)-type cytochromecoxidases andba(3)-type ubiquinol oxidase. In the present study, we focused on strains expressing only one of these enzymes. The competition experiments showed that possession ofcbb(3)-type oxidase confers significant fitness advantage during oxygen-limited growth and supports the biofilm lifestyle. Theaa(3)-type oxidase was shown to allow rapid aerobic growth at a high oxygen supply. Activity of the denitrification pathway that had been expressed in cells grown anaerobically with nitrate was fully inhibitable by oxygen only in wild-type andcbb(3)strains, while in strainsaa(3)andba(3)dinitrogen production from nitrate and oxygen consumption occurred simultaneously. Together, the results highlight the importance of thecbb(3)-type oxidase for the denitrification phenotype and suggest a way of obtaining novel bacterial strains capable of aerobic denitrification.