FIGURE 1: The genetics and schematics of D-serine uptake in E. coli.

(A) Genetic organization of the D-serine tolerance and D-serine sensory loci in pathogenic EHEC and UPEC. D-serine tolerance is achieved via uptake (dsdX – blue) and catabolism (dsdA) of D-serine under the control of a transcriptional regulator, DsdC. This system is truncated in EHEC. D-serine uptake but not catabolism is achieved via YhaO (red), which is also required for virulence of EHEC.

(B) Model of D-serine uptake and its downstream effects in EHEC and UPEC. UPEC transports D-serine via DsdX and YhaO, but only DsdX is responsive in this genetic background. UPEC uses D-serine as a positive virulence and fitness trait. EHEC regulates D-serine transport via YhaO and accumulates it intracellularly as a signal for stress and regulator of virulence.