A sodium ion gradient as energy source for Peptostreptococcus asaccharolyticus

Area of Science:

• Microbial metabolism and bioenergetics
• Anaerobic fermentation pathways
• Bacterial growth and energy conservation

Background:

• Glutamate fermentation is a key metabolic process in certain anaerobic bacteria.
• Understanding energy generation in these organisms is crucial for microbiology and biotechnology.
• Previous pathways for glutamate fermentation were incomplete.

Purpose of the Study:

• To elucidate the detailed metabolic pathway of glutamate fermentation in Acidaminococcus fermentans and Peptostreptococcus asaccharolyticus.
• To quantify ATP generation through substrate-level phosphorylation.
• To investigate the role of sodium gradients in bacterial growth and energy conservation.

Main Methods:

• Enzymatic activity assays in cell-free extracts.
• Analysis of fermentation end-products (acetate, butyrate).
• Bacterial growth experiments with and without monensin, a sodium ionophore.

Main Results:

• A refined pathway for glutamate fermentation via (R)-2-hydroxyglutarate to acetate and butyrate was established.
• Substrate-level phosphorylation yielded calculated ATP amounts.
• Sodium gradients were found to provide additional energy for growth in multiple bacterial species.
• Energy conservation via the Na+ gradient in P. asaccharolyticus was quantified (up to 0.6 mol ATP per mol glutaconyl-CoA decarboxylated).

Conclusions:

• The biotin-dependent glutaconyl-CoA decarboxylase plays a significant role in energy conservation through sodium gradients.
• The findings provide a mechanistic explanation for the growth-promoting effects of monensin in cattle.
• This research enhances our understanding of bioenergetic strategies in anaerobic bacteria.