FIG. 4.
Number of fluorescent foci correlates with extracellular protease activity. V. cholerae gfp-epsC and PBAD::eps gfp-epsC cells producing the type II-dependent protease VC1200 were supplemented with IPTG at a final concentration of 100 μM and grown to mid-log stage. In the case of PBAD::eps gfp-epsC (pVC1200), 0.001% or 0.01% arabinose was added to the cultures. The GFP-EpsC-expressing cells were analyzed by fluorescence microscopy, and for each expression condition, the number of fluorescent foci in 200 cells was scored. Protease activity in mid-log culture supernatants was assayed by measuring methylcoumarin fluorescence generated from Boc-Gln-Ala-Arg-7-amido-4-methylcoumarin hydrolysis, and rates were normalized to OD600. The average of at least three experiments is presented ± the standard error of the mean.