Integrative expression vectors with P promoters for inducer-free overproduction of recombinant proteins in .

Inducer-free integrative vectors are often used to create strains for industrial purposes, but employing strong promoters to produce high levels of recombinant proteins in results in high leaky expression that can hamper cloning in . To overcome the problem, we used strong IPTG-inducible P promoters harboring operators to construct inducer-free integrative vectors able to integrate into the genome at either the or the locus, or both and examined their ability to repress the β-galactosidase () gene in and to overexpress BgaB in . The P01 vectors could repress expression about 24-fold in to low background levels. The integrated P01- constructs exhibited inducer-free expression and produced 8% of total cellular proteins, only 1.25 or 1.75 times less compared with their cognates as plasmids. The stronger promoters, P100- and P212- yielded 20.9 % and 42 % of total intracellular proteins after 12 h of incubation, respectively. Incorporation of the P212- into both and loci resulted in BgaB expression up to 53.4 %. In conclusion, integrative vectors containing the P promoter family have great potential for inducer-free overproduction of recombinant proteins in .