BackgroundMembrane- and membrane-associated proteins are important for the pathogenicity of bacteria. We have analysed the content of these proteins in virulent Mycobacterium tuberculosis H37Rv using Triton X-114 detergent-phase separation for extraction of lipophilic proteins, followed by their identification with high resolution mass spectrometry.ResultsIn total, 1417 different proteins were identified. In silico analysis of the identified proteins revealed that 248 proteins had at least one predicted trans-membrane region. Also, 64 of the identified proteins were predicted lipoproteins, and 54 proteins were predicted as outer membrane proteins. Three-hundred-and-ninety-five of the observed proteins, including 91 integral membrane proteins were described for the first time. Comparison of abundance levels of the identified proteins was performed using the exponentially modified protein abundance index (emPAI) which takes into account the number of the observable peptides to the number of experimentally observed peptide ions for a given protein. The outcome showed that among the membrane-and membrane-associated proteins several proteins are present with high relative abundance. Further, a close examination of the lipoprotein LpqG (Rv3623) which is only detected in the membrane fractions of M. tuberculosis but not in M. bovis, revealed that the homologous gene in M. bovis lack the signal peptide and lipobox motif, suggesting impaired export to the membrane.ConclusionsAltogether, we have identified a substantial proportion of membrane- and membrane-associated proteins of M. tuberculosis H37Rv, compared the relative abundance of the identified proteins and also revealed subtle differences between the different members of the M. tuberculosis complex.

BackgroundThe potential causes for variation in virulence between distinct M. tuberculosis strains are still not fully known. However, differences in protein expression are probably an important factor. In this study we used a label-free quantitative proteomic approach to estimate differences in protein abundance between two closely related M. tuberculosis strains; the virulent H37Rv strain and its attenuated counterpart H37Ra.ResultsWe were able to identify more than 1700 proteins from both strains. As expected, the majority of the identified proteins had similar relative abundance in the two strains. However, 29 membrane-associated proteins were observed with a 5 or more fold difference in their relative abundance in one strain compared to the other. Of note, 19 membrane- and lipo-proteins had higher abundance in H37Rv, while another 10 proteins had a higher abundance in H37Ra. Interestingly, the possible protein-export membrane protein SecF (Rv2586c), and three ABC-transporter proteins (Rv0933, Rv1273c and Rv1819c) were among the more abundant proteins in M. tuberculosis H37Rv.ConclusionOur data suggests that the bacterial secretion system and the transmembrane transport system may be important determinants of the ability of distinct M. tuberculosis strains to cause disease.

Coinfection with human immunodeficiency virus type 1 (HIV-1) and opportunistic mycobacteria, especially Mycobacterium tuberculosis, is a cause of high morbidity and mortality worldwide. Both mycobacteria and HIV-1 may infect macrophages, and thus, coinfection may generate conditions that reciprocally influence the intracellular replication of the pathogens. Elucidation of the interaction between HIV-1 and mycobacteria in their common target cell is important for understanding pathogenesis in coinfected individuals. In this study, we investigated the effects of in vitro HIV-1 infection on the growth of M. tuberculosis, M. avium, and M. paratuberculosis in human peripheral blood monocyte-derived macrophages. Interestingly, HIV-1 infection induced a greater bacterial burden in coinfected cell cultures for all of the mycobacterial species tested and specifically induced accelerated growth of M. tuberculosis with a reduced mean generation time. The interaction of HIV-1 and M. tuberculosis was especially detrimental to the host cell, causing a significant synergistic reduction in macrophage viability. Also, in M. tuberculosis/HIV-1-coinfected cultures, increased levels of interleukin-1␤ (IL-1␤), IL-6, IL-8, and granulocyte-macrophage colony-stimulating factor were observed and viral replication was enhanced. Overall, the present data suggest that HIV-1 infection of macrophages may impair their ability to contain mycobacterial growth. Furthermore, coinfection with HIV-1 and M. tuberculosis seems to give rise to synergistic effects at the cellular level that mutually enhance the replication of both pathogens. This may, in part, contribute to the increased morbidity and mortality seen in coinfected individuals.Human immunodeficiency virus type 1 (HIV-1) has caused a global pandemic, and approximately 33.4 million people were living with HIV infection by the end of 2008 (34). HIV ϩ individuals have an increased susceptibility to a wide range of opportunistic bacterial infections (reviewed in references 2 and 25). However, infections with certain opportunistic organisms like Mycobacterium tuberculosis are of particular concern, as people in resource-poor countries are often struck disproportionately hard, with increased morbidity and mortality due to the relatively high prevalence of HIV-1 and mycobacterial coinfections and limited access to appropriate treatment.In the clinical context of HIV-1 infection, M. tuberculosis and M. avium complex (MAC) infections are the most frequent. These mycobacteria display various propensities to cause disease. Notably, M. tuberculosis is the leading cause of death in HIV ϩ patients and a major public health concern, while MAC infections are typically seen in the later stages of HIV infection, when the adaptive immunity of the host is compromised. By current classical genetic criteria, the MAC consists of mainly two species, M. intracellulare and M. avium, and M. avium is further subdivided into three subsets, M. avium subsp. avium (here referred to as M. avium) M. avium subsp. paratuber...