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

## TL;DR

This paper shows how two gut pathogens evolved different ways to use a sugar called D-ribulose, giving them a competitive edge in the gut.

## Contribution

The study reveals distinct and convergent D-ribulose utilization pathways in attaching and effacing pathogens, providing new mechanistic insights.

## Key findings

- EHEC uses the Aau transporter to import D-ribulose in the presence of L-arabinose, which is then metabolized via AraB.
- Citrobacter rodentium uses a dedicated D-ribulose transport and kinase system distinct from EHEC.
- Both pathogens have evolved convergent strategies to exploit D-ribulose for gut colonization.

## Abstract

Attaching and effacing pathogens overcome colonisation resistance by competing with metabolically similar organisms for limited resources. Enterohaemorrhagic E. coli (EHEC) utilises the pathogenicity island-encoded Accessory ʟ-arabinose Uptake (Aau) transporter to effectively colonise the mouse gut, hypothesised to be achieved via an enhanced capacity to scavenge ʟ-arabinose. Aau is regulated exclusively in response to ʟ-arabinose, but it is unclear how this system specifically benefits EHEC in vivo. Here, we show that Aau displays a > 200-fold higher affinity for the monosaccharide D-ribulose, over ʟ-arabinose. EHEC cannot grow on D-ribulose as a sole carbon source and this sugar does not trigger aau transcription. However, Aau effectively transports D-ribulose into the cell only in the presence of ʟ-arabinose, where it feeds into the pentose phosphate pathway, after phosphorylation by the ʟ-ribulokinase AraB, thus providing EHEC a significant fitness advantage. EHEC has therefore evolved a mechanism of hijacking the canonical ʟ-arabinose utilisation machinery to promote D-ribulose utilisation in vivo. Furthermore, Citrobacter rodentium encodes an analogous system that exclusively transports D-ribulose and metabolises it via a dedicated D-ribulokinase. These unique mechanisms of D-ribulose utilisation suggest that convergent evolution has driven the ability of distinct pathogenic species to exploit this nutrient during invasion of the gut niche.

Cottam et al. identify distinct pathways for D-ribulose utilisation in pathogenic Escherichia coli and Citrobacter rodentium, providing mechanistic details and suggesting convergent evolution towards utilisation of this nutrient in nature.