Efficient Secretion of the β-Galactosidase Bgal1-3 via both Tat-Dependent and Tat-Independent Pathways in Bacillus subtilis.

In this study, the twin-arginine (Tat) signal peptide PhoD was used to direct the secretion of the β-galactosidase Bgal1-3 into the growth medium of an engineered strain of Bacillus subtilis 168. After 24 h of cultivation, the extracellular activity reached 1.15 U/mL, representing 78% of the total activity. Bgal1-3 was exported via both Tat-dependent and Tat-independent pathways. To improve the secretion amounts, two more copies of the target gene were inserted into the designated loci on the chromosome, further improving the extracellular enzymatic activity to 2.15 U/mL. The engineered strain with three copies of bgal1-3 was genetically stable after 150 generations. To the best of our knowledge, this is the first report on the functional secretion of a heterologous protein via both Tat-dependent and Tat-independent pathways mediated by a Tat signal peptide in B. subtilis. Furthermore, this study provides us with a markerless engineered strain for the production of β-galactosidase.