Different Functions of Phylogenetically Distinct Bacterial Complex I Isozymes

Area of Science:

• Microbiology
• Biochemistry
• Bioenergetics

Background:

• NADH:quinone oxidoreductase (complex I) is crucial for energy conservation in mitochondria via NADH oxidation.
• Its role in bacterial electron transport chains is less understood, despite diverse bacterial lifestyles.

Purpose of the Study:

• To investigate the function of two distinct complex I isozymes in Rhodobacter sphaeroides.
• To determine the contribution of these isozymes to bacterial respiration and growth under various conditions.

Main Methods:

• Genetic analysis of Rhodobacter sphaeroides strains lacking complex I isozymes.
• Phenotypic characterization of growth under aerobic, anaerobic, photoautotrophic, and photoheterotrophic conditions.

Main Results:

• Rhodobacter sphaeroides complex I activity is vital for aerobic respiration and anaerobic DMSO respiration.
• The two complex I isozymes (complex IA and complex IE) are essential for photoautotrophic and photoheterotrophic growth.
• Complex IA is important for routing electrons to nitrogenase for H2 production, while complex IE is not.

Conclusions:

• The two complex I isozymes in R. sphaeroides are not functionally redundant.
• Phylogenetically distinct bacterial complex I enzymes have evolved to support diverse metabolic strategies and lifestyles.