Figure 2

Expression plasmids used for the synthesis of BG. (I) Gene E expression under the chemical inducer T7-lactose (lac) promoter operator (PO) system with the lac repressor (lacI) regulatory element. In this system, bacteria are allowed to grow until 0.3 OD_600nm and then gene E is induced by the addition of a chemical inducer, IPTG (II) Gene E expression under the temperature sensitive lambda promoter (λpR) with the thermo-sensitive repressor c1857 regulatory element. In this system, bacteria are allowed to grow until 0.3 OD_600nm and then gene E is induced by thermal shift to 42 °C. (III) Gene E expression under the λpR with dual c1857 and arabinose-inducible araC protein regulatory elements. The λpR promoter with the thermolabile repressor cI857 suppresses the lysis gene transcription under 28 °C for the normal growth of the bacterial cells. However, the λpR promoter system may be leaky leading to undesired expression of the lysis gene. In this system, the leaky expression of gene E at 28 °C is avoided by the anti-sense RNA of the lysis gene produced by the ParaBAD promoter in the presence of L-arabinose that binds to its complementary sense RNA of the lysis gene caused by the leaky λpR promoter.