In order to test the hypothesis that Hvo_0405 is a Tat substrate, samples from the membrane and cytoplasm of strains expressing Hvo_0405RR or the mutated Hvo_0405KK were analyzed by mass spectrometry. A semi-enzymatic peptid corresponding to the cleavage of the signal peptide could only be identified in for Hvo_0405RR, indicating that Hvo_0405 is indeed a Tat substrate.