Staphylococcus aureus nuclease is a useful secretion reporter for mycobacteria

A secretion reporter system based on Staphylococcus aureus nuclease (nuc) was developed for use in mycobacteria. Fusion of secretion signals to the reporter cloned in a shuttle vector, pBPnuc1, resulted in halo formation around colonies of Mycobacterium smegmatis and Mycobacterium tuberculosis grown on DNase agar plates containing Methyl Green indicator dye. This in-situ detection system was used to identify secreted proteins by screening a pBPnuc1::H37Rv nuc gene fusion library in M. smegmatis. The clones identified in this screen all formed colony halos when present in M. tuberculosis grown on indicator media. The proteins corresponded to DesA2, a stearoyl-acyl carrier protein desaturase, PepA, a putative serine protease and the Apa antigen, which is the ATP-binding subunit of an ABC transport system. Of these proteins, only PepA and Apa contained recognizable leader peptides.