for two purposes.
Assessing the relative carbenicillin resistances of the deletion strains compared to the wild type
strain would allow us to determine whether regulation of these genes may be involved in carbenicillin
resistance, and to determine whether the βLR16 regulator gene impacts resistance in
the absence of either of the porin genes. The kanamycin resistance cassette insertions in the
ΔompC and ΔompF strains (Table 1) precluded use of the pCRC03UVRA subclone in these
strains, owing to the kanamycin resistance selectable marker in the vector. Comparing the
empty vector (pCF430)MIC values between the K-12-derived strain (BW25113, the progenitor
for the Keio knockout collection [28]) and the two porin knockout strains, the data suggested
that elimination of the OmpF porin increases carbenicillin resistance while elimination of the
OmpC porin renders E. coli more sensitive to carbenicillin. The βLR16 clone enhances carbenicillin
resistance in each of the strains, with the greatest difference between empty vector and
βLR16 resistance in the ΔompC strain. This is consistent with downregulation of ompF expression
as a means of carbenicillin resistance, but the enhanced resistance conferred by βLR16 in
the ΔompF strain suggests the involvement of additional mechanisms.