Bacterial reduction of trimethylamine oxide

Area of Science:

• Microbiology
• Bacterial Physiology
• Biochemistry

Background:

• Trimethylamine N-oxide (TMAO) is abundant in marine animal tissues.
• TMAO acts as an electron acceptor in anaerobic metabolism for diverse bacteria.
• Bacterial reduction of TMAO to trimethylamine is a significant cause of marine fish spoilage.

Purpose of the Study:

• To investigate the role of TMAO in bacterial anaerobic respiration.
• To elucidate the electron transport pathways involved in TMAO reduction.
• To understand the regulation and genetic basis of TMAO respiration in different bacterial groups.

Main Methods:

• Analysis of electron transport components (flavin nucleotides, menaquinones, cytochromes, molybdoenzyme reductase).
• Identification of electron donors for TMAO respiration (formate, hydrogen, lactate, glycerol, TCA cycle intermediates).
• Electrophoretic separation and characterization of constitutive and induced TMAO reductases.
• Genetic mapping of genes involved in TMAO respiration.
• Comparative studies with nitrate and dimethyl sulfoxide reduction.

Main Results:

• TMAO reduction supports oxidative phosphorylation in Enterobacteriaceae and Alteromonas.
• Specific electron transport chains involving various redox cofactors facilitate TMAO respiration.
• TMAO respiration is repressed by oxygen and nitrate.
• Distinct TMAO reductases are synthesized, with some being inducible.
• The structural gene for inducible TMAO reductase is not yet fully identified.
• Alteromonas requires NaCl for growth on TMAO and exhibits similarities to aerobic respiration.

Conclusions:

• Bacterial TMAO reduction is a versatile metabolic process supporting energy generation across different environments.
• The electron transport pathways and regulation of TMAO respiration are complex and vary among bacterial groups.
• Further research is needed to fully understand TMAO's role, especially in nonsulfur purple bacteria, and to identify key genes.