cbb ₃ -Type Cytochrome c Oxidases, Aerobic Respiratory Enzymes, Impact the Anaerobic Life of Pseudomonas aeruginosa PAO1

Abstract

For bacteria, many studies have focused on the role of respiratory enzymes in energy conservation; however, their effect on cell behavior is poorly understood. Pseudomonas aeruginosa can perform both aerobic respiration and denitrification. Previous studies demonstrated that cbb 3 -type cytochrome c oxidases that support aerobic respiration are more highly expressed in P. aeruginosa under anoxic conditions than are other aerobic respiratory enzymes. However, little is known about their role under such conditions. In this study, it was shown that cbb 3 oxidases of P. aeruginosa PAO1 alter anaerobic growth, the denitrification process, and cell morphology under anoxic conditions. Furthermore, biofilm formation was promoted by the cbb 3 oxidases under anoxic conditions. cbb 3 oxidases led to the accumulation of nitric oxide (NO), which is produced during denitrification. Cell elongation induced by NO accumulation was reported to be required for robust biofilm formation of P. aeruginosa PAO1 under anoxic conditions. Our data show that cbb 3 oxidases promote cell elongation by inducing NO accumulation during the denitrification process, which further leads to robust biofilms. Our findings show that cbb 3 oxidases, which have been well studied as aerobic respiratory enzymes, are also involved in denitrification and influence the lifestyle of P. aeruginosa PAO1 under anoxic conditions. R espiration is a fundamental process for energy conservation. In eukaryotic mitochondria, aa 3 -type cytochrome c oxidase (terminal oxidase) catalyzes the terminal reaction of electron transport in aerobic respiration through oxygen reduction. Furthermore, the generation of reactive oxygen species (ROS) and the oxidation of cytochrome c by aa 3 oxidase can induce apoptosis; thus, aa 3 oxidase also plays a role in cell fate determination (1, 2). In bacteria, multiple terminal oxidases have been reported to catalyze energy conservation; however, few studies have reported their influence on cell behavior.Pseudomonas aeruginosa is a ubiquitous bacterium with versatile aerobic and anaerobic respiratory systems (3). Under oxic environments, five terminal oxidases (Cyo, CIO, aa 3 , cbb 3 -1, and cbb 3 -2) reduce oxygen as terminal electron acceptors. The terminal oxidases Cyo and CIO are quinol oxidases, while the terminal oxidases aa 3 and cbb 3 are cytochrome c oxidases. Compared with other terminal oxidases, cbb 3 oxidases possess a high affinity for oxygen. cbb 3 -1 and cbb 3 -2 oxidases are encoded by the tetracistronic ccoNOQP-1 and ccoNOQP-2 operons (4). The ccoNOQP-1 operon is constitutively transcribed under various oxygen concentrations (5). On the other hand, the ccoNOQP-2 operon is highly transcribed under low oxygen concentrations because the oxygen-responsive transcriptional regulator ANR upregulates its promoter activity. These enzymatic and transcriptional characteristics of cbb 3 oxidases enable P. aeruginosa to grow in low-oxygen environments. In addition, under anoxic conditions, where oxygen is depleted, P. aeruginosa can u...

Origin and Impact of Nitric Oxide in Pseudomonas aeruginosa Biofilms

“…As shown by Yoon and coworkers and confirmed in a more recent study (64,65), P. aeruginosa PAO1 cells grown anaerobically are more elongated than that grown aerobically and easily form highly cohesive clumps, yielding a robust biofilm. Cell elongation is dependent on the presence of NIR and is repressed in the presence of an NO antagonist.…”

Identification and Characterization of the Novel Subunit CcoM in the cbb 3 -Cytochrome c Oxidase from Pseudomonas stutzeri ZoBell

“…In contrast, the ANR-independent one is constitutively expressed and not directly dependent on oxygen concentrations ( 8 , 39 ). Recently, Hamada and coworkers showed that the P. aeruginosa cbb 3 -C c Os accumulate nitric oxide and are involved in biofilm formation during the anaerobic denitrification process ( 40 ). In addition, cbb 3 -C c Os were reported to be expressed under anaerobic conditions in several other bacterial species, e.g., Shewanella oneidensis , Bradyrhizobium japonicum , and Rhodobacter capsulatus ( 19 , 41 , 42 ).…”

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