Complementation of the Lactococcus lactis Secretion Machinery with Bacillus subtilis SecDF Improves Secretion of Staphylococcal Nuclease

Unlike Bacillus subtilis and Escherichia coli, the gram-positive lactic acid bacterium Lactococcus lactis does not possess the SecDF protein, a component of the secretion (Sec) machinery involved in late secretion stages and required for the high-capacity protein secretion in B. subtilis. In this study, we complemented the L. lactis Sec machinery with SecDF from B. subtilis and evaluated the effect on the secretion of two forms of staphylococcal nuclease, NucB and NucT, which are efficiently and poorly secreted, respectively. The B. subtilis SecDF-encoding gene was tested in L. lactis at different levels. Increased quantities of the precursor and mature forms were observed only at low levels of SecDF and at high NucT production levels. This SecDF secretion enhancement was observed at the optimal growth temperature (30°C) and was even greater at 15°C. Furthermore, the introduction of B. subtilis SecDF into L. lactis was shown to have a positive effect on a secreted form of Brucella abortus L7/L12 antigen.