Convergent evolution of distinct D-ribulose utilisation pathways in attaching and effacing pathogens

Area of Science:

• Microbiology
• Molecular Biology
• Pathogen-Host Interactions

Background:

• Attaching and effacing pathogens compete for resources, overcoming colonization resistance.
• Enterohaemorrhagic E. coli (EHEC) uses the Accessory L-arabinose Uptake (Aau) transporter for gut colonization, potentially by scavenging L-arabinose.
• The specific in vivo benefit of the Aau transporter in EHEC remains unclear.

Purpose of the Study:

• To elucidate the in vivo function and substrate specificity of the EHEC Aau transporter.
• To understand how EHEC gains a fitness advantage in the gut environment.

Main Methods:

• Investigated the substrate affinity of the Aau transporter for D-ribulose and L-arabinose.
• Assessed the role of D-ribulose and L-arabinose in EHEC growth and Aau transporter regulation.
• Examined the metabolic fate of D-ribulose within EHEC.

Main Results:

• The Aau transporter exhibits a significantly higher affinity for D-ribulose (>200-fold) than for L-arabinose.
• EHEC cannot metabolize D-ribulose as a sole carbon source, nor does it induce Aau transcription.
• Aau transports D-ribulose in the presence of L-arabinose, feeding it into the pentose phosphate pathway via L-ribulokinase (AraB), conferring a fitness advantage.
• Citrobacter rodentium possesses a similar system for D-ribulose utilization.

Conclusions:

• EHEC has evolved a mechanism to utilize D-ribulose by hijacking the L-arabinose utilization pathway.
• This D-ribulose utilization provides a significant fitness advantage for EHEC during gut colonization.
• Convergent evolution has led distinct pathogenic species to exploit D-ribulose in the gut niche.