Futile xylitol cycle in Lactobacillus casei

Area of Science:

• Microbiology
• Biochemistry

Background:

• Lactobacillus casei Cl-16 growth can be inhibited by xylitol.
• The metabolic pathways involved in this inhibition were not fully understood.

Purpose of the Study:

• To elucidate the mechanism of xylitol-mediated growth inhibition in Lactobacillus casei Cl-16.
• To identify the key enzymes and transport systems involved in the futile xylitol cycle.

Main Methods:

• Investigated the metabolic fate of xylitol in Lactobacillus casei Cl-16.
• Analyzed the role of the xylitol-specific phosphoenolpyruvate-dependent phosphotransferase system.
• Examined the effects of xylitol metabolism on intracellular phosphate pools and energy production.

Main Results:

• Identified a futile xylitol cycle responsible for growth inhibition.
• Demonstrated that xylitol is phosphorylated to xylitol-5-phosphate by a gratuitously induced phosphotransferase.
• Showed that this cycle leads to rapid depletion of ribitol-5-phosphate and cellular energy, causing bacteriostasis.

Conclusions:

• The futile xylitol cycle is the primary mechanism for xylitol-mediated growth inhibition in Lactobacillus casei.
• Disruption of ribitol-5-phosphate metabolism and energy supply underlies the observed bacteriostasis.