E. coli strains XLl-blue

The used plasmid pEScFv is a eukaryotic expression vector containing an AM single-chain Fv (ScFv) fragment linked with domain B of a protein A of S. aureus. Sp2/0 myeloma cells transfected with pEScFv 2G42D7 secreted ScFv into the culture media. E. coli strain XLl/Blue is transformed with plasmid pEScFv... 

E. coli XLl-Blue was grown at 37°C in Luria-Bertani (LB) medium (containing 10 g/L of tryptone, 5 g/L of yeast extract, and 5 g/L of NaCl). Recombinant E. coli strains for the PHA production were cultivated at 30°C for 72 h in LB medium containing two different carbon sources (1) 2 g/L of sodium decanoate (Sigma, St. Louis, MO) and (2) 10 g/L of sodium gluconate (Junsei, Tokyo, Japan) plus 2 g/L of sodium decanoate. All the flask cultures were carried out in triplicate in a rotary shaker at 250 rpm. For the cultivation of recombinant E. coli strains, ampicillin (50 mg/L) was added to the medium. 

There are two possible reasons for these differences in yield. First, the pUC19 might be a better expression vector for pha operon in this case, and therefore a higher amount of PHA accumulated. Second, the capacity of PHA synthesis in different E. coli strains was different because the metabolite may be different in E. coli HMS174 and E. coli XLl-Blue. 

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