Fig. 2.

Heterologous protein production and activity of aminopeptidase PepN in L. lactis. (A) Expression of the membrane protein BcaP-GFP-H6 was induced in L. lactis strains NZ9000 and JP9000, both carrying plasmid pNZbcaP-GFP-H6 (12). The strains were grown in GM17 until an optical density (OD) at 600 nm of 0.5 was reached, after which they were induced for 1 h with 5 ng/ml of nisin. Mean fluorescence, as measured by flow cytometry, of the plasmid-carrying strains normalized to that of plasmid-free L. lactis NZ9000 is plotted. The uninduced bar depicts the fluorescence of the noninduced JP9000 (pNZbcaP-GFP-H6) culture. (B) PepN activity in L. lactis strains MG1363 (9), NZ9000 (11), MG1363ΔpepN (16), and JP9000 (this work) was determined in cell extracts of cultures grown in GM17 until an OD at 600 nm of 0.5, by monitoring the hydrolysis of the PepN substrate lysyl-p-nitroanilide, as described previously (8). Data (A and B) are the averages of 4 biological replicates, and the error bars are the associated standard deviations.