Abstract: The efficiency of inactivating bacterial hosts of staphylococcal nuclease A (SNA) is at one order of magnitude higher when it is expressed in a thermo-inducible single expression system than in a dual expressing system combined with simultaneously expressing lysis gene E for bacterial ghost preparation. To explore possible mechanisms causing this difference, SNA was cloned into a thermo-inducible dual expressing vector and its enzymatic activity was analyzed after induction. Results showed that intracellular and extracellular products of SNA were detectable at 30 min and 90 min, respectively after induction and all possess nuclease activity. The percentage of inactivated host bacteria was 99.7% 4 h after induction, with the host genomic DNA successfully degraded. These indicated that the expression of SNA in a thermo-inducible dual expressing vector without simultaneously expression of lysis gene E could still kill the host strain as efficiently as in a single expressing system. The co-expression of SNA and lysis gene E in the dual expressing vector might be the major reason resulting in lower inactivation efficiency of SNA.

Key words: staphylococcal nuclease A, bacterial ghosts, lysis gene E