TABLE 1.
E. coli strains and plasmids
| Strain or plasmida | Relevant genotype and/or phenotypeb | Reference |
|---|---|---|
| Strains | ||
| BW25113 | lacIqrrnBT14 ΔlacZwj16hsdR514 ΔaraBADAH33 ΔrhaBADLD78 | 7 |
| W3110 | F-IN(rrnD-rrnE)1 | 23 |
| KP1456 | W3110 ΔexbBD tolQ(Am)37 | 18 |
| RA1003 | W3110 ΔexbBD::kan | 32 |
| RA1034 | W3110 ΔexbBD::kan ΔtolR | This study |
| RA1035 | W3110 ΔtolQR | This study |
| RA1044 | W3110 ΔexbB ΔtolR | This study |
| RA1045 | W3110 ΔtolQR ΔexbD | This study |
| RA1046 | W3110 ΔtolQR ΔexbB | This study |
| RA1051 | W3110 ΔexbBD::kan ΔtolQR | This study |
| Plasmids | ||
| pBAD24 | araBAD promoter, AraC, Ampr | 16 |
| pKP392 | pBAD24 araBAD-regulated exbB | 18 |
| pKP393 | pBAD24 araBAD-regulated exbD | This study |
| pRA001 | pBAD24 araBAD-regulated tolQ | This study |
| pRA002 | pBAD24 araBAD-regulated tolR | This study |
| pRA003 | pBAD24 araBAD-regulated tolQR | This study |
The identity of each plasmid construct generated in this study was confirmed by sequence determination.
The specific nature of each of the deletions involving exbB, exbD, tolQ, and tolR is as follows. The ΔexbBD deletion of KP1456 is a large, incompletely characterized deletion involving the exbBD operon and the adjacent metC gene, originally isolated by Guterman and Dann (15). The ΔexbBD::kan mutation involves the replacement of all but the initiation codon of exbB (codons 2 to 244) and its TAA termination codon, the six intervening nucleotides, and all of the codons of exbD (codons 1 to 141) by the kan gene from pACYC177, as previously described (32). The ΔexbB deletion removed exbB codons 1 to 244, the TAA termination codon, and the six additional nucleotides that occur prior to the exbD initiation codon. The ΔexbD deletion removed exbD codons 1 to 141 and the TAA termination codon. The ΔtolQR deletion removed tolQ codons 1 to 230, the TAA termination codon, the three nucleotides that occur prior to the tolR initiation codon, all 142 tolR codons, and the TAA termination codon. The ΔtolR deletion removed tolR codons 1 to 142 and the TAA termination codon.