Abstract
Enterobacter cloacae IFO 3320 exhibits chemotactic responses to inorganic phosphate (Pi) when starved of Pi. One Tn1737KH-induced mutant failed to exhibit Pi taxis even under conditions of Pi limitation. The mutant showed normal chemotactic responses to amino acids and citrate, suggesting that it is specifically defective in Pi taxis. Southern blot analysis revealed that the insertion Tn1737KH was located in the indigenous plasmid pEC01. The pEC01-cured strain of IFO 3320 did not show Pi taxis even under conditions of Pi limitation, indicating that pEC01 is required for Pi taxis in E. cloacae IFO 3320. This plasmid is 5002 bp long, consisting of four mobilization genes, mbeCABD, and an origin of replication homologous to ColE1-type plasmids. pEC01 contains no open reading frame (ORF) encoding a protein with a highly conserved motif of methyl-accepting chemotaxis proteins (MCPs), suggesting that a gene encoding a MCP responsible for Pi taxis is located on the chromosome. An ORF encoding a putative protein of 102 amino acids was responsible for the complementation of the pEC01-cured strain. The putative protein had a helix-turn-helix motif, suggesting that it is involved in the gene regulation of the Pi taxis MCP gene.
