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Abstract
The outer membrane protein A (OmpA) is a major protein in Escherichia coli outer membrane. The expression of omp A is tightly correlated to temperature stress, with lower expression at higher growth temperature. Combined with the observation that transformation of E. coli growing at a lowered temperature has higher transformation efficiency when using CaCl, OmpA could potentially play a role in chemical transformation. In order to determine 2 the effect of OmpA on the transformation efficiency, two strains of E. coli, BW25113 (WT omp A) and JW0940-6 intended om pA deletion/insertion mutation), were grown at different temperatures. The relative levels of OmpA were compared after a membrane protein isolation step. SDS-PAGE and PCR were used to confirm the expression of omp A and genotypes of both strains respectively. SDS-PAGE analysis revealed that both strains had omp A expression and PCR revealed that the JW0940-6 strain contained the entire omp A coding region. Both WT and intended ∆ omp A strains showed higher transformation efficiency when grown at 42 ℃ compared to 37 ℃. However, 20 ℃ growth temperature promoted transformation efficiency in BW25113 but lowered transformation efficiency in the JW0940-6. Overall, the results implied that, in the JW0940-6 strains obtained, either the kanamycin resistance cassette was inserted into a different gene or the strain had intrinsic kanamycin resistance. Without omp A deletion strain and accurate protein assay for protein gel loading, the data were not sufficient to support the original hypothesis that omp A expression affected transformation efficiency.