Differences in two Pseudomonas aeruginosa cbb3 cytochrome oxidases

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• Bacterial cytochrome cbb3 oxidases are key for energy conservation in proteobacteria, particularly under low oxygen.
• Pseudomonas aeruginosa uniquely has two potential cbb3 oxidase operons: cbb3-1 and cbb3-2.

Purpose of the Study:

• To investigate the distinct metabolic and regulatory roles of the two cbb3 oxidase isoforms in Pseudomonas aeruginosa.
• To understand their functions across different oxygen tensions.

Main Methods:

• Comparative analysis of cbb3-1 and cbb3-2 abundance and expression under varying oxygen levels.
• Assessment of growth phenotypes in mutant strains lacking functional cbb3 oxidases.
• Examination of the impact of cbb3 oxidase activity on alternative oxidase (CioAB) expression and signal transduction pathways.

Main Results:

• Cytochrome cbb3-1 is metabolically important at high oxygen tensions, with greater abundance and expression than cbb3-2.
• Loss of cbb3-1, but not cbb3-2, significantly impacted bacterial growth in highly aerated cultures.
• Cbb3-1 activity inhibited CioAB expression, influencing a signal transduction pathway, similar to Rhodobacter sphaeroides.
• Cbb3-2 played a more critical role under oxygen limitation, with increased abundance and expression regulated by the Anr protein.

Conclusions:

• Each Pseudomonas aeruginosa cbb3 oxidase isoform (cbb3-1 and cbb3-2) has evolved specialized energetic and regulatory functions.
• Cbb3-1 is primarily active and influential under high oxygen conditions, while cbb3-2 is optimized for low oxygen environments.
• These findings elucidate the functional divergence of duplicated respiratory enzymes within a single bacterial species.