[Cloning, expression of phospholipase A1 from Serratia liquefaciens and auto-induction fermentation by lactose]

To produce recombinant phospholipase A(1) (PLA(1)) by Escherichian coli, the pla gene encoding PLA(1) was amplified from Serratia liquefaciens by PCR and cloned into two vectors pET20-b(+) and pET28-a(+). The two recombinant plasmids were then transformed into E. coli BL21 (DE3) individually to express PLA(1). E. coli BL21(DE3)/pET28a-pla yielded extracellular PLA(1) with an activity of 40.8 U/mL in batch cultivations of shaken flasks by auto-induction, which was accounted for 91% of total enzyme activity. On the basis of primal auto-induction medium, the optimized fermentation medium of PLA(1) contained tryptone 10 g/L, yeast extract 5 g/L, glucose 0.8 g/L, lactose 5 g/L, Na2HPO4 25 mmol/L, KH2PO4 25 mmol/L and 1 mmol/L MgSO4 (final concentration). Glycine (7.5 g/L) was added 6 h after inoculated. After incubated at 37 degrees C for 24 h, extracellular enzyme activity reached 128.7 U/mL.