Environmental temperature regulates transcription of a virulence pili operon in E. coli

The expression in Escherichia coli K-12 of a pilus-adhesion determinant, obtained through molecular cloning from a pyelonephritic E. coli isolate, was studied at different temperatures. Strain HB101 carrying the recombinant plasmid pRHU845 agglutinated human erythrocytes after growth at 37 degrees C but not after growth at 22 degrees C. Quantitation of pilus subunit protein by an enzyme-linked immunosorbent assay (ELISA) for pilus antigen showed that synthesis of the pilus subunits was reduced at least 20-fold at 22 degrees C as compared with 37 degrees C. The 5' end of the pilus subunit structural gene, papA, was fused to the lacZ gene such that expression could be monitored at both translational and transcriptional levels. Measurements of beta-galactosidase production by the papA-lacZ hybrids provided evidence for thermoregulation of papA gene transcription. A regulatory determinant was localized to a 2-kb EcoRI-HindIII fragment encoding the papB gene and part of papA although none of the presently known pap gene products seem to be directly involved in a thermoregulatory mechanism. Comparison with other thermoregulatory systems in E. coli suggests that pap gene expression is regulated by a novel mechanism.