Proteins primarily regarded as cytoplasmic have consistently been identified in the exoproteomes of different bacterial species, and moonlighting roles in the extracellular environment have already been demonstrated for some of them [31, 32], including evasion of host’s immune system [42], adhesion to host cells [43, 44], folding of extracytoplasmic proteins [41, 45], and interaction between microorganisms [40, 46]. Noteworthy, specific evidences for active secretion of such cytoplasmic proteins have been demonstrated for only a few examples to date, and demonstration

of an extracellular function is still missing for many of these proteins [30, 31]. The variant exoproteome may account for differential virulence of the two C. pseudotuberculosis strains A considerable number (49/93) of the extracellular proteins identified C646 mw in this work was observed in only one of the two strains studied, then composing a variant experimental C. pseudotuberculosis exoproteome (additional files 3 and 4). Highly variant exoproteomes

have also been reported recently for other Gram+ bacterial pathogens [20, 36, 39, 47–49], and such a variation may be considered an important factor leading to the observable learn more phenotypic dissimilarities and ultimately to differential virulence of the various strains [50, 51]. Hecker et al. [36] reported on how the composition of the exoproteome can vary extremely within a single species, Staphylococcus aureus, being that only 7 out of 63 identified extracellular proteins were found in all the twenty-five clinical isolates studied.

One of the most intriguing results in the present study was the detection of the phospholipase D (PLD) protein only in the extracellular proteome of the strain C231 (additional file 4). As the regulation of PLD expression was demonstrated to be complex and highly affected by multiple environmental factors [52], we sought to detect this protein in the culture supernatant of the C. pseudotuberculosis 1002 strain grown in a rich medium (brain-heart infusion broth) Caspase-dependent apoptosis instead of only chemically-defined medium (CDM), but these attempts were also Palbociclib in vitro unfruitful (data not shown). Besides, we were not able to detect secretion of PLD following total exoproteome analysis of the 1002 strain grown under specific stress generating conditions (Pacheco et al., unpublished). The results strongly indicate that this protein is actually not being secreted by the 1002 strain in culture. PLD is an exotoxin considered as the major virulence factor of C. pseudotuberculosis [5, 52]. It possesses sphingomyelinase activity that contributes to endothelial permeability and then to spreading of the bacteria within the host [5]. Mutation of the pld gene in C.