The allele encoding the mycobacterial Erp protein affects lung disease in mice

Comparison of the transcriptome, lipidome, and c-di-GMP production between BCGΔBCG1419c and BCG, with Mincle- and Myd88-dependent induction of proinflammatory cytokines in murine macrophages

We have previously reported the transcriptomic and lipidomic profile of the first-generation, hygromycin-resistant (HygR) version of the BCGΔBCG1419c vaccine candidate, under biofilm conditions. We recently constructed and characterized the efficacy, safety, whole genome sequence, and proteomic profile of a second-generation version of BCGΔBCG1419c, a strain lacking the BCG1419c gene and devoid of antibiotic markers. Here, we compared the antibiotic-less BCGΔBCG1419c with BCG. We assessed their colonial and ultrastructural morphology, biofilm, c-di-GMP production in vitro, as well as their transcriptomic and lipidomic profiles, including their capacity to activate macrophages via Mincle and Myd88. Our results show that BCGΔBCG1419c colonial and ultrastructural morphology, c-di-GMP, and biofilm production differed from parental BCG, whereas we found no significant changes in its lipidomic profile either in biofilm or planktonic growth conditions. Transcriptomic profiling suggests changes in BCGΔBCG1419c cell wall and showed reduced transcription of some members of the DosR, MtrA, and ArgR regulons. Finally, induction of TNF-α, IL-6 or G-CSF by bone-marrow derived macrophages infected with either BCGΔBCG1419c or BCG required Mincle and Myd88. Our results confirm that some differences already found to occur in HygR BCGΔBCG1419c compared with BCG are maintained in the antibiotic-less version of this vaccine candidate except changes in production of PDIM. Comparison with previous characterizations conducted by OMICs show that some differences observed in BCGΔBCG1419c compared with BCG are maintained whereas others are dependent on the growth condition employed to culture them.

Identification and Characterization of Osmoregulation Related MicroRNAs in Gills of Hybrid Tilapia Under Three Types of Osmotic Stress

Researchers have increasingly suggested that microRNAs (miRNAs) are small non-coding RNAs that post-transcriptionally regulate gene expression and protein translation in organs and respond to abiotic and biotic stressors. To understand the function of miRNAs in osmotic stress regulation of the gills of hybrid tilapia (Oreochromis mossambicus ♀ × Oreochromis urolepis hornorum ♂), high-throughput Illumina deep sequencing technology was used to investigate the expression profiles of miRNAs under salinity stress (S, 25‰), alkalinity stress (A, 4‰) and salinity-alkalinity stress (SA, S: 15‰, A: 4‰) challenges. The results showed that 31, 41, and 27 upregulated and 33, 42, and 40 downregulated miRNAs (P < 0.05) were identified in the salt stress, alkali stress, and saline-alkali stress group, respectively, which were compared with those in the control group (C). Fourteen significantly differently expressed miRNAs were selected randomly and then validated by a quantitative polymerase chain reaction. On the basis of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis, genes related to osmoregulation and biosynthesis were enriched in the three types of osmotic stress. In addition, three miRNAs and three predicted target genes were chosen to conduct a quantitative polymerase chain reaction in the hybrid tilapia and its parents during 96-h osmotic stress. Differential expression patterns of miRNAs provided the basis for research data to further investigate the miRNA-modulating networks in osmoregulation of teleost.

Immune responses elicited by the recombinant Erp, HspR, LppX, MmaA4, and OmpA proteins from Mycobacterium tuberculosis in mice

Immunogenic potency of the recombinant Erp, HspR, LppX, MmaA4, and OmpA proteins from Mycobacterium tuberculosis (MTB), formulated with Montanide ISA 720 VG adjuvant, was evaluated in BALB/c mice for the first time in this study. The five vaccine formulations, adjuvant, and BCG vaccine were subcutaneously injected into mice, and the sera were collected at days 0, 15, 30, 41, and 66. The humoral and cellular immune responses against vaccine formulations were determined by measuring serum IgG and serum interferon-gamma (IFN-γ) and interleukin-12 (IL-12) levels, respectively. All formulations significantly increased IgG levels post-vaccination. The highest increase in IFN-γ level was provided by MmaA4 formulation. The Erp, HspR, and LppX formulations were as effective as BCG in enhancement of IFN-γ level. The most efficient vaccine boosting the IL-12 level was HspR formulation, especially at day 66. Erp formulation also increased the IL-12 level more than BCG at days 15 and 30. The IL-12 level boosted by MmaA4 formulation was found to be similar to that by BCG. OmpA formulation was inefficient in enhancement of cellular immune responses. This study showed that MmaA4, HspR, and Erp proteins from MTB are successful in eliciting both humoral and cellular immune responses in mice.

Microbial Offense vs Host Defense: Who Controls the TB Granuloma?

The granuloma is the hallmark of tuberculosis and simultaneously signifies acquisition of an infection and induction of a host immune response. But who benefits more from the development of the granuloma, the host or the pathogen? Is microbe or man dictating disease course and progression? Mycobacterial diseases affect humans and animals alike, and the concepts presented in this review reflect host-pathogen interactions that influence not only mycobacterial granulomas in humans and animals but also other infectious granulomatous diseases that are encountered in veterinary medicine. Current dogma supports that an organized granuloma is a mark of an adequate and “restrictive” host immune response. However, the formation of a granuloma also provides a niche for the maturation, growth, and persistence of numerous infectious agents, and these pathogens devote some portion of their genetic machinery to ensuring these structures’ form. An understanding of pathogens’ contributions to granuloma formation can aid the development of host-directed therapies and other antimicrobial and antiparasitic therapies that can tip this balance in favor of a restrictive host response and elimination—not just containment—of the infectious organism. This review discusses animal models that have aided our understanding of pathogens’ contribution to the host response and how mycobacterial virulence genes direct host pathology in ways that may aid disease transmission and/or persistence in the form of latent infection.

Interaction of Erp Protein of Mycobacterium tuberculosis with Rv2212 Enhances Intracellular Survival of Mycobacterium smegmatis

The Mycobacterium tuberculosis exported repetitive protein (RvErp) is a crucial virulence-associated factor as determined by its role in the survival and multiplication of mycobacteria in cultured macrophages and in vivo Although attempts have been made to understand the function of Erp protein, its exact role in Mycobacterium pathogenesis is still elusive. One way to determine this is by searching for novel interactions of RvErp. Using a yeast two-hybrid assay, an adenylyl cyclase (AC), Rv2212, was found to interact with RvErp. The interaction between RvErp and Rv2212 is direct and occurs at the endogenous level. The Erp protein of Mycobacterium smegmatis (MSMEG_6405, or MsErp) interacts neither with Rv2212 nor with Ms_4279, the M. smegmatis homologue of Rv2212. Deletion mutants of Rv2212 revealed its adenylyl cyclase domain to be responsible for the interaction. RvErp enhances Rv2212-mediated cyclic AMP (cAMP) production. Also, the biological significance of the interaction between RvErp and Rv2212 was demonstrated by the enhanced survival of M. smegmatis within THP-1 macrophages. Taken together, these studies address a novel mechanism by which Erp executes its function.

IMPORTANCE

RvErp is one of the important virulence factors of M. tuberculosis This study describes a novel function of RvErp protein of M. tuberculosis by identifying Rv2212 as its interacting protein. Rv2212 is an adenylyl cyclase (AC) and produces cAMP, one of the prime second messengers that regulate the intracellular survival of mycobacteria. Therefore, the significance of investigating novel interactions of RvErp is paramount in unraveling the mechanisms governing the intracellular survival of mycobacteria.

Identification of Novel Potential Vaccine Candidates against Tuberculosis Based on Reverse Vaccinology

Tuberculosis (TB) is a chronic infectious disease, considered as the second leading cause of death worldwide, caused by Mycobacterium tuberculosis. The limited efficacy of the bacillus Calmette-Guérin (BCG) vaccine against pulmonary TB and the emergence of multidrug-resistant TB warrants the need for more efficacious vaccines. Reverse vaccinology uses the entire proteome of a pathogen to select the best vaccine antigens by in silico approaches. M. tuberculosis H37Rv proteome was analyzed with NERVE (New Enhanced Reverse Vaccinology Environment) prediction software to identify potential vaccine targets; these 331 proteins were further analyzed with VaxiJen for the determination of their antigenicity value. Only candidates with values ≥0.5 of antigenicity and 50% of adhesin probability and without homology with human proteins or transmembrane regions were selected, resulting in 73 antigens. These proteins were grouped by families in seven groups and analyzed by amino acid sequence alignments, selecting 16 representative proteins. For each candidate, a search of the literature and protein analysis with different bioinformatics tools, as well as a simulation of the immune response, was conducted. Finally, we selected six novel vaccine candidates, EsxL, PE26, PPE65, PE_PGRS49, PBP1, and Erp, from M. tuberculosis that can be used to improve or design new TB vaccines.

Hyper-attenuated MTBVAC erp mutant protects against tuberculosis in mice

Safety of individuals at risk of immune suppression is an important concern for live vaccines. The new-generation tuberculosis vaccine candidate MTBVAC, a genetically engineered doubly attenuated Mycobacterium tuberculosis mutant with deletions in phoP and fadD26 virulence genes has demonstrated comparable safety in different relevant animal models and superior protection in mice as compared to the only currently licensed tuberculosis vaccine Mycobacterium bovis BCG. Here we describe the construction of a highly attenuated MTBVAC-based live vaccine by an additional gene inactivation generated in erp of MTBVAC. The gene product of erp is an exported repeated protein (Erp), a virulence factor described to be involved in intracellular replication of M. tuberculosis. The resultant strain, MTBVAC erp(-), was tested in severe combined immunodeficiency (SCID) mouse model showing to be severely attenuated when compared to BCG and MTBVAC. Experiments conducted in immunocompetent mice revealed that the hyper-attenuated profile observed with MTBVAC erp(-) strain did not compromise its protective efficacy profile in comparison with BCG. These results postulate MTBVAC erp(-) as a potential tuberculosis vaccine candidate for use in high-risk populations of immune suppression (e.g., due to HIV infection), where the use of BCG is not recommended.

Mycobacteria manipulate macrophage recruitment through coordinated use of membrane lipids

The evolutionary survival of Mycobacterium tuberculosis, the cause of human tuberculosis (TB), depends on its ability to invade the host, replicate, and transmit infection. At its initial peripheral infection site in the distal lung airways, M. tuberculosis infects macrophages which transport it to deeper tissues¹. How mycobacteria survive in these broadly microbicidal cells is an important question. Here we show that M. tuberculosis, and its close pathogenic relative Mycobacterium marinum, preferentially recruit and infect permissive macrophages while evading microbicidal ones. This immune evasion is accomplished by using cell surface associated phthiocerol dimycoceroserate (PDIM) lipids² to mask underlying pathogen-associated molecular patterns (PAMPs). In the absence of PDIM, these PAMPs signal a toll-like receptor (TLR)-dependent recruitment of macrophages that produce microbicidal reactive nitrogen species. Concordantly, the related phenolic glycolipids (PGL)², promote recruitment of permissive macrophages via a host chemokine receptor 2 (CCR2)-mediated pathway. Thus, we have identified coordinated roles for PDIM, known to be essential for mycobacterial virulence³ and PGL, which (along with CCR2) is known to be associated with human TB^4,5. Our findings also suggest an explanation for the longstanding observation that M. tuberculosis initiates infection in the relatively sterile environment of the lower respiratory tract, rather than in the upper respiratory tract, where resident microflora and inhaled environmental microbes may continually recruit microbicidal macrophages through TLR-dependent signaling.

Virulence factors of the Mycobacterium tuberculosis complex

The Mycobacterium tuberculosis complex (MTBC) consists of closely related species that cause tuberculosis in both humans and animals. This illness, still today, remains to be one of the leading causes of morbidity and mortality throughout the world. The mycobacteria enter the host by air, and, once in the lungs, are phagocytated by macrophages. This may lead to the rapid elimination of the bacillus or to the triggering of an active tuberculosis infection. A large number of different virulence factors have evolved in MTBC members as a response to the host immune reaction. The aim of this review is to describe the bacterial genes/proteins that are essential for the virulence of MTBC species, and that have been demonstrated in an in vivo model of infection. Knowledge of MTBC virulence factors is essential for the development of new vaccines and drugs to help manage the disease toward an increasingly more tuberculosis-free world.

Identification of two proteins that interact with the Erp virulence factor from Mycobacterium tuberculosis by using the bacterial two-hybrid system

Background

The exported repetitive protein (erp) gene encodes a secreted 36-kDa protein with a central domain containing several proline-glycine-leucine-threonine-serine (PGLTS) repeats. It has been demonstrated that erp is a virulence-associated factor since the disruption of this gene impairs the growth of Mycobacterium bovis and Mycobacterium tuberculosis in mice.

Results

In order to elucidate the function of Erp we searched for Erp-binding proteins from M. tuberculosis by using a bacterial two-hybrid system. Our results indicate that Erp interacts specifically with two putative membrane proteins, Rv1417 and Rv2617c. Further analysis revealed that the latter two interact with each other, indicating that Rv1417, Rv2617c and Erp are connected through multiple interactions. While Rv1417 is disseminated in several Actinomycetales genera, orthologues of Rv2617c are exclusively present in members of the M. tuberculosis complex (MTC). The central and amino-terminal regions of Erp were determined to be involved in the interaction with Rv1417 and Rv2627c. Erp forms from Mycobacterium smegmatis and Mycobacterium leprae were not able to interact with Rv2617c in two-hybrid assays. Immunolocalization experiments showed that Rv1417 and Rv2617c are found on the cell membrane and Erp on the bacterial cell wall. Finally, comparative genomics and expression studies revealed a possible role of Rv1417 in riboflavin metabolism.

Conclusion

We identified interactive partners of Erp, an M. tuberculosis protein involved in virulence, which will be the focus of future investigation to decipher the function of the Erp family protein.

Global transcriptional profile of Mycobacterium tuberculosis during THP-1 human macrophage infection

During lung infection, Mycobacterium tuberculosis resides in macrophages and subverts the bactericidal mechanisms of these professional phagocytes. Comprehension of this host-pathogen relationship is fundamental for the development of new therapies to cure and prevent tuberculosis. In this work, we analyzed the transcriptional profile of M. tuberculosis infecting human macrophage-like THP-1 cells in order to identify putative bacterial pathogenic factors that can be relevant for the intracellular survival of M. tuberculosis. We compared the gene expression profile of M. tuberculosis H37Rv after 4 h and 24 h of infection of human macrophage-like THP-1 cells with the gene expression profile of the strain growing exponentially in broth cultures. We found 585 genes expressed differentially by intracellular M. tuberculosis. An analysis of the gene expression profile of M. tuberculosis inside THP-1 cells suggests the perturbation of the cell envelope as a major intracellular stress inside THP-1 macrophages.

The evolving story of Mycobacterium tuberculosis clade members detected in fish

Advances in molecular analyses have permitted documentation of an increasing spectrum of mycobacteria infecting fish. Although some of these mycobacteria are not closely related, several species belong to the Mycobacterium tuberculosis clade. One member of the clade, M. marinum, is well known as an agent of piscine mycobacteriosis. Three other clade species, M. shottsii, M. pseudoshottsii and M. 'chesapeaki', have recently been identified as predominant disease agents in a widespread, continuing epizootic in wild striped bass of the Chesapeake Bay. A fifth clade member, M. ulcerans, has recently been indirectly detected in wild, African cichlid fish. As M. ulcerans is the third most common human mycobacterial infection worldwide, even such indirect evidence of M. ulcerans in fish must be more thoroughly investigated. Complicating the differentiation of these clade members is the growing recognition of intraspecies and interspecies variation in phenotypes, genes and virulence. Thus, researchers must be aware of the variety of piscine isolates within the M. tuberculosis clade. This review summarizes the methods of detection and differentiation for this important group of mycobacteria.

Mycobacterium marinum Erp is a virulence determinant required for cell wall integrity and intracellular survival

The Mycobacterium tuberculosis exported repetitive protein (Erp) is a virulence determinant required for growth in cultured macrophages and in vivo. To better understand the role of Erp in Mycobacterium pathogenesis, we generated a mutation in the erp homologue of Mycobacterium marinum, a close genetic relative of M. tuberculosis. erp-deficient M. marinum was growth attenuated in cultured macrophage monolayers and during chronic granulomatous infection of leopard frogs, suggesting that Erp function is similarly required for the virulence of both M. tuberculosis and M. marinum. To pinpoint the step in infection at which Erp is required, we utilized a zebrafish embryo infection model that allows M. marinum infections to be visualized in real-time, comparing the erp-deficient strain to a DeltaRD1 mutant whose stage of attenuation was previously characterized in zebrafish embryos. A detailed microscopic examination of infected embryos revealed that bacteria lacking Erp were compromised very early in infection, failing to grow and/or survive upon phagocytosis by host macrophages. In contrast, DeltaRD1 mutant bacteria grow normally in macrophages but fail to induce host macrophage aggregation and subsequent cell-to-cell spread. Consistent with these in vivo findings, erp-deficient but not RD1-deficient bacteria exhibited permeability defects in vitro, which may be responsible for their specific failure to survive in host macrophages.

Mutation in the P36 gene of Mycobacterium bovis provokes attenuation of the bacillus in a mouse model

P36 is a member of a family of secreted proteins distributed throughout the genus Mycobacterium. The central domain of these proteins contains several amino acid PGLTS repeats, which differ considerably between species. P36, also called exported repetitive protein (Erp) in M. tuberculosis, has been shown to be associated with virulence since the disruption of its gene impaired multiplication of both virulent M. tuberculosis and M. bovis BCG in cultured macrophages and immunocompetent mice. In order to demonstrate that P36 is a putative virulence factor of wild-type Mycobacterium bovis we generated a P36 mutant by gene disruption and we evaluated its replication in spleen and lungs of infected mice. In this study, the mutant strain displays low levels of multiplication in mice, indicating that the P36 gene is important for in vivo growth of M. bovis.

Mycobacterium pseudoshottsii sp. nov., a slowly growing chromogenic species isolated from Chesapeake Bay striped bass (Morone saxatilis)

A group of slowly growing photochromogenic mycobacteria was isolated from Chesapeake Bay striped bass (Morone saxatilis) during an epizootic of mycobacteriosis. Growth characteristics, acid-fastness and 16S rRNA gene sequencing results were consistent with those of the genus Mycobacterium. Biochemical reactions, growth characteristics and mycolic acid profiles (HPLC) resembled those of Mycobacterium shottsii, a non-pigmented mycobacterium also isolated during the same epizootic. Sequencing of the 16S rRNA genes, the gene encoding the exported repeated protein (erp) and the gene encoding the 65 kDa heat-shock protein (hsp65) and restriction enzyme analysis of the hsp65 gene demonstrated that this group of isolates is unique. Insertion sequences associated with Mycobacterium ulcerans, IS2404 and IS2606, were detected by PCR. These isolates could be differentiated from other slowly growing pigmented mycobacteria by their inability to grow at 37 °C, production of niacin and urease, absence of nitrate reductase, negative Tween 80 hydrolysis and resistance to isoniazid (1 μg ml−1), p-nitrobenzoic acid, thiacetazone and thiophene-2-carboxylic hydrazide. On the basis of this polyphasic study, it is proposed that these isolates represent a novel species, Mycobacterium pseudoshottsii sp. nov. The type strain, L15T, has been deposited in the American Type Culture Collection as ATCC BAA-883T and the National Collection of Type Cultures (UK) as NCTC 13318T.

A mutant of Mycobacterium tuberculosis H37Rv that lacks expression of antigen 85A is attenuated in mice but retains vaccinogenic potential

The fbpA and fbpB genes encoding the 85A and 85B proteins of Mycobacterium tuberculosis H37Rv, respectively, were disrupted, the mutants were examined for their ability to survive, and the strain lacking 85A (DeltafbpA) was tested for its ability to immunize mice. The DeltafbpA mutant was attenuated in mice after intravenous or aerosol infection, while replication of the DeltafbpB mutant was similar to that of the wild type. Complementation of the fbpA gene in DeltafbpA restored its ability to grow in the lungs of mice. The DeltafbpA mutant induced a stronger expression of pulmonary mRNA messages in mice for tumor necrosis factor alpha, interleukin-1 beta (IL-1beta), gamma interferon, IL-6, IL-2, and inducible nitric oxide (NO) synthase, which led to its decline, while H37Rv persisted despite strong immune responses. H37Rv and DeltafbpA both induced NO in macrophages and were equally susceptible to NO donors, although DeltafbpA was more susceptible in vitro to peroxynitrite and its growth was enhanced by NO inhibitors in mice and macrophages. Aerosol-infected mice, which cleared a low-dose DeltafbpA infection, resisted a challenge with virulent M. tuberculosis. Mice subcutaneously immunized with DeltafbpA or Mycobacterium bovis BCG and challenged with M. tuberculosis also showed similar levels of protection, marked by a reduction in the growth of challenged M. tuberculosis. The DeltafbpA mutant was thus attenuated, unlike DeltafbpB, but was also vaccinogenic against tuberculosis. Attenuation was incomplete, however, since DeltafbpA revived in normal mice after 370 days, suggesting that revival was due to immunosenescence but not compensation by the fbpB or fbpC gene. Antigen 85A thus affects susceptibility to peroxynitrite in M. tuberculosis and appears to be necessary for its optimal growth in mice.

The hydrophobic domain of the Mycobacterial Erp protein is not essential for the virulence of Mycobacterium tuberculosis

Erp (exported repetitive protein) is a member of a mycobacterium-specific family of extracellular proteins. A hydrophobic region that is localized at the C-terminal domain and that represents a quarter of the protein is highly conserved across species. Here we show that this hydrophobic region is not essential for restoring the virulence and tissue damage of an erp::aph mutant strain of M. tuberculosis as assessed by bacterial counts and lung histology analysis in a mouse model of tuberculosis.

The Erp protein is anchored at the surface by a carboxy-terminal hydrophobic domain and is important for cell-wall structure in Mycobacterium smegmatis

Erp (Exported Repetitive Protein), also known as P36, Pirg and Rv3810, is a member of a mycobacteria-specific family of extracellular proteins. In pathogenic species, the erp gene has been described as a virulence factor. The Erp proteins comprise three domains. The N- and C-terminal domains are similar in all mycobacterial species, while the central domain consists of a repeated module that differs considerably between species. Here we show that the Erp protein is loosely attached to the surface and that the carboxy-terminal domain, which displays hydrophobic features, anchors Erp at the surface of the bacillus. The hydrophobic region is not necessary for the complementation of the altered colony morphology of a Mycobacterium smegmatis erp- mutant but proved to be necessary to achieve resistance to detergent at wild-type levels.

Inactivation of the Mycobacterium bovis homologue of the polymorphic RD1 gene Rv3879c (Mb3909c) does not affect virulence

The RD1 locus is deleted from all strains of Mycobacterium bovis BCG but present in virulent isolates of M. bovis and Mycobacterium tuberculosis. The RD1 gene Rv3879c encodes a proline- and alanine-rich protein that shows sequence polymorphism across members of the M. tuberculosis complex. The role of this protein in virulence was investigated by deleting the Rv3879c homologue from M. bovis (Mb3909c) and testing the virulence of the mutant in the guinea pig model. The M. bovis Delta Mb3909c mutant was not attenuated in the guinea pig model, showing that this gene does not encode a virulence factor and plays no role in the attenuation caused by loss of RD1.

Different susceptibility of two animal species infected with isogenic mutants of Mycobacterium bovis identifies phoT as having roles in tuberculosis virulence and phosphate transport

The Mycobacterium tuberculosis complex includes Mycobacterium bovis, which causes tuberculosis in most mammals, including humans. In previous work, it was shown that M. bovis ATCC 35721 has a mutation in its principal sigma factor gene, sigA, causing a single amino acid change affecting binding of SigA with the accessory transcription factor WhiB3. ATCC 35721 is avirulent when inoculated subcutaneously into guinea pigs but can be restored to virulence by integration of wild-type sigA to produce M. bovis WAg320. Subsequently, it was surprising to discover that WAg320 was not virulent when inoculated intratracheally into the Australian brushtail possum (Trichosurus vulpecula), a marsupial that is normally very susceptible to infection with M. bovis. In this study, an in vivo complementation approach was used with ATCC 35721 to produce M. bovis WAg322, which was virulent in possums, and to identify the virulence-restoring gene, phoT. There are two point deletions in the phoT gene of ATCC 35721 causing frameshift inactivation, one of which is also in the phoT of BCG. Knockout of phoT from ATCC 35723, a virulent strain of M. bovis, produced M. bovis WAg758, which was avirulent in both guinea pigs and possums, confirming that phoT is a virulence gene. The effect on virulence of mode of infection versus animal species susceptibility was investigated by inoculating all the above strains by aerosol into guinea pigs and mice and comparing these to the earlier results. Characterization of PhoT indicated that it plays a role in phosphate uptake at low phosphate concentrations. At least in vitro, this role requires the presence of a wild-type sigA gene and appears separate from the ability of phoT to restore virulence to ATCC 35721. This study shows the advantages of using different animal models as tools for the molecular biological investigation of tuberculosis virulence.