Improvement of TAC125 as a Cell Factory: IPTG-Inducible Plasmid Construction and Strain Engineering.

Our group has used the marine bacterium TAC125 (TAC125) as a platform for the successful recombinant production of "difficult" proteins, including eukaryotic proteins, at low temperatures. However, there is still room for improvement both in the refinement of TAC125 expression plasmids and in the bacterium's intrinsic ability to accumulate and handle heterologous products. Here, we present an integrated approach of plasmid design and strain engineering finalized to increment the recombinant expression and optimize the inducer uptake in TAC125. To this aim, we developed the IPTG-inducible plasmid pP79 and an engineered TAC125 strain called KrPL . This mutant was designed to express the lactose permease and to produce only a truncated version of the endogenous Lon protease through an integration-deletion strategy. In the wild-type strain, pP79 assured a significantly better production of two reporters in comparison to the most recent expression vector employed in TAC125. Nevertheless, the use of KrPL was crucial to achieving satisfying production levels using reasonable IPTG concentrations, even at 0 °C. Both the wild-type and the mutant recombinant strains are characterized by an average graded response upon IPTG induction and they will find different future applications depending on the desired levels of expression.