Isolation and characterization of Enterobacter cloacae mutants which are defective in chemotaxis toward inorganic phosphate

Enterobacter cloacae IFO3320 is attracted to Pi when cells are starved for Pi. Two Tn1737KH-induced mutants, which were constitutive for alkaline phosphatase, failed to exhibit Pi taxis even under conditions of Pi limitation. Both of the mutant strains exhibited normal chemotactic responses to peptone, suggesting that they are specifically defective in Pi taxis. Cloning and sequence analysis showed that the TN1737KH insertions were located in either the pstA or pstB genes which encode the channel-forming proteins of the Pi-specific transport (Pst) system in E. cloacae. These results suggest that the E. cloacae Pst system is required for Pi chemoreception.