Fig. 6

Optimization of aprE expression in different genome loci and analysis effect analysis of different strains. a Genome locations to be inserted the aprE expression cassette in B. licheniformis (GenBank Number: CP033218), I-the symmetrical position of the aprE (2,419,710-2,422,710 bp), II-near the origin of replication (321,526-322,944 bp), III-the symmetrical position of the replication origin (3,396,863-3,397,860 bp); b Confirmation of the integrated mutants by screening the single-crossover recombinant and the double-crossover mutant. BL I1, BL I2, BL I3 correct single-crossover recombinant individually with a band of 700 bp (b-1), 900 bp (b-3) and 700 bp (b-5) (the band can’t be amplified if no precise single-crossover) and correct double-crossover mutant with 2760 bp (b-2), 3070 bp (b-4) and 2740 bp (b-6) band (the band were 3100 bp, 1500 bp and 1200 bp if no correct double-crossover mutant); c Investigation of the aprE expression level of different integrating strains. The left Y axis indicated AprE enzyme activityand the right Y axis indicated aprE transcriptional level