A program of Yersinia enterocolitica type III secretion reactions is activated by specific signals.

Successful establishment of Yersinia infections requires the type III machinery, a protein transporter that injects virulence factors (Yops) into macrophages. It is reported here that the Yersinia type III pathway responds to environmental signals by transporting proteins to distinct locations. Yersinia enterocolitica cells sense an increase in extracellular amino acids (glutamate, glutamine, aspartate, and asparagine) that results in the activation of the type III pathway. Another signal, provided by serum proteins such as albumin, triggers the secretion of YopD into the extracellular medium. The third signal, a decrease in calcium concentration, appears to be provided by host cells and causes Y. enterocolitica to transport YopE and presumably other virulence factors across the eukaryotic plasma membrane. Mutations in several genes encoding regulatory molecules (lcrG, lcrH, tyeA, yopD, yopN, yscM1, and yscM2) bypass the signal requirement of the type III pathway. Together these results suggest that yersiniae may have evolved distinct secretion reactions in response to environmental signals.