Glucose prevents citrate metabolism by enterococci

Area of Science:

• Microbiology
• Bacterial Metabolism
• Enzyme Kinetics

Background:

• Enterococcus species are common bacteria found in various environments.
• Citrate metabolism is an important metabolic pathway for many microorganisms.
• Understanding the regulation of citrate metabolism is crucial for comprehending bacterial physiology.

Purpose of the Study:

• To investigate the influence of glucose and pH on citrate metabolism in Enterococcus faecalis and Enterococcus faecium.
• To determine the optimal conditions for citrate utilization by these bacterial species.
• To explore the potential for catabolite repression in Enterococcus citrate metabolism.

Main Methods:

• Culturing Enterococcus strains (E. faecalis FAIR E-239, E. faecalis FAIR E-237, E. faecalis FAIR E-259, E. faecium FAIR E-338, E. faecium FAIR E-371) on different media (glucose, citrate, glucose plus citrate).
• Measuring citrate metabolism rates at various pH values (5.5, 6.5, 7.5, 8.5) and citrate concentrations (<10 mM, >10 mM).
• Assessing citrate metabolism in resting cells from different growth phases (log vs. stationary) and growth conditions.

Main Results:

• Enterococcus faecalis FAIR E-239 metabolized citrate at pH 6.5 and 7.5 only after glucose depletion, but not at pH 5.5 or 8.5.
• Glucose significantly inhibited citrate metabolism in all tested Enterococcus strains.
• Citrate-grown resting cells showed optimal citrate metabolism at pH 4.7, with significant activity at pH 4.2 and 6.5, and faster metabolism at lower citrate concentrations (<10 mM).

Conclusions:

• Glucose acts as a repressor of citrate metabolism in Enterococcus species, indicating catabolite repression.
• pH significantly influences citrate utilization, with optimal conditions varying between growth states.
• Bacterial growth phase and substrate concentration also play roles in the efficiency of citrate metabolism.