Surface-exposed glycopeptidolipids of Mycobacterium smegmatis specifically inhibit the phagocytosis of mycobacteria by human macrophages. Identification of a novel family of glycopeptidolipids

Use of stable isotope combined with intact cell lipidomic by routine MALDI mass spectrometry analysis for rapid drug susceptibility assay in mycobacteria

RATIONALE

Rapid, accurate, and easy-to-perform diagnostic assays are required to address the current need for the diagnosis of resistant pathogens. That is particularly the case for mycobacteria, such as the human pathogen Mycobacterium tuberculosis, which requires up to 2 weeks for the determination of the drug susceptibility profile using the conventional broth microdilution method. To address this challenge, we investigated the incorporation of deuterium, the stable isotope of hydrogen, into lipids as a read out of the drug susceptibility profile.

METHODS

Deuterium is incorporated into newly synthesized proteins or lipids in place of hydrogen as bacterial cells grow, increasing the mass of the macromolecules, which can then be observed via matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). As proof-of-concept, we used the non-pathogenic Mycobacterium smegmatis mc2155 strain, which is susceptible to the aminoglycoside antibiotic kanamycin, and M. smegmatis mc2155 containing the empty vector pVV16, which is kanamycin-resistant. Bacteria were incubated in a culture medium containing 50% of deuterium oxide (D2O) and either 1 or 2 times the minimal inhibitory concentration (MIC50) of kanamycin. Lipids were then analyzed using the MBT lipid Xtract matrix combined with routine MALDI mass spectrometry in the positive ion mode to evaluate the changes in the lipid profile.

RESULTS

Using this approach, we were able to distinguish susceptible from resistant bacteria in less than 5 h, a process that would take 72 h using the conventional broth microdilution method.

CONCLUSIONS

We therefore propose a solution for the rapid determination of drug susceptibility profiles using a phenotypic assay combining D2O stable isotope labelling and lipid analysis by routine MALDI mass spectrometry.

A dTDP-L-rhamnose 4-epimerase required for glycopeptidolipid biosynthesis in Mycobacterium abscessus

Mycobacterium abscessus causes severe lung infections in cystic fibrosis patients and exhibits smooth (S) or rough (R) morphotypes. Disruption of glycopeptidolipid (GPL) production results in the S-to-R transition but the underlying molecular mechanisms of this transition remain incompletely understood. Herein, we characterized MAB_4111c in relation to GPL synthesis and investigated the effects of MAB_4111c deletion in M. abscessus pathogenicity. An enzymatic assay indicated that MAB_4111c, also designated Tle for Talose epimerase, is converting dTDP-L-Rhamnose into dTDP-6-deoxy-L-Talose. A tle deletion mutant was constructed in the S variant of M. abscessus and relative areas of Rhamnose and 6-deoxy-Talose and their methylated forms expressed as ratios of total monosaccharides, showed an altered GPL profile lacking 6-deoxy-Talose. Thus, Tle provides dTDP-6-deoxy-L-Talose, subsequently used by the glycosyltransferase Gtf1 to transfer 6-deoxy-Talose to the GPL backbone. Strikingly, the tle mutant exhibited an R morphotype, showed impaired sliding motility and biofilm formation, and these phenotypes were rescued upon functional complementation. Moreover, deletion of tle in M. abscessus results in increased pathogenicity and killing in zebrafish embryos. Together, our results underscore the importance of the dTDP-L-Rhamnose 4-epimerase activity in GPL biosynthesis and in influencing M. abscessus virulence.

Multiple Mycobacterium abscessus O-acetyltransferases influence glycopeptidolipid structure and colony morphotype

Mycobacterium abscessus causes severe lung infections. Clinical isolates can have either smooth (S) or rough (R) colony morphotypes; of these, S but not R variants have abundant cell wall glycopeptidolipids (GPL) consisting of a peptidolipid core substituted by a 6-deoxy-α-L-talose (6-dTal) and rhamnose residues. Deletion of gtf1, encoding the 6-dTal transferase, results in the S-to-R transition, mycobacterial cord formation, and increased virulence, underscoring the importance of 6-dTal in infection outcomes. However, since 6-dTal is di-O-acetylated, it is unclear whether the gtf1 mutant phenotypes are related to the loss of the 6-dTal or the result of the absence of acetylation. Here, we addressed whether M. abscessus atf1 and atf2, encoding two putative O-acetyltransferases located within the gpl biosynthetic locus, transfer acetyl groups to 6-dTal. We found deletion of atf1 and/or atf2 did not drastically alter the GPL acetylation profile, suggesting there are additional enzymes with redundant functions. We subsequently identified two paralogs of atf1 and atf2, MAB_1725c and MAB_3448. While deletion of MAB_1725c and MAB_3448 had no effect on GPL acetylation, the triple atf1-atf2-MAB_1725c mutant did not synthetize fully acetylated GPL, and the quadruple mutant was totally devoid of acetylated GPL. Moreover, both triple and quadruple mutants accumulated hyper-methylated GPL. Finally, we show deletion of atf genes resulted in subtle changes in colony morphology but had no effect on M. abscessus internalization by macrophages. Overall, these findings reveal the existence of functionally redundant O-acetyltransferases and suggest that O-acetylation influences the glycan moiety of GPL by deflecting biosynthetic flux in M. abscessus.

Ferritin from Mycobacterium abscessus is involved in resistance to antibiotics and oxidative stress

Mycobacterium abscessus subsp. massiliense (Mycma) is a rapidly growing Mycobacterium belonging to the M. abscessus complex that is often associated with lung and soft tissue infection outbreaks. Mycma is resistant to many antimicrobials, including those used for treating tuberculosis. Therefore, Mycma infections are difficult to treat and may lead to high infectious complication rates. Iron is essential for bacterial growth and establishment of infection. During infection, the host reduces iron concentrations as a defense mechanism. To counteract the host-induced iron deficiency, Mycma produces siderophores to capture iron. Mycma has two ferritins (encoded by mycma_0076 and mycma_0077) modulated by different iron concentrations, which allow the survival of this pathogen during iron scarcity. In this study, we constructed knockout (Mycma 0076KO) and complemented (Mycma 0076KOc) gene strains for mycma_0076 to understand the function of 0076 ferritin. Deletion of mycma_0076 in Mycma led to the transition in colony morphology from smooth to rough, alteration of the glycopeptidolipids spectra, increased permeability of the envelope, reduction in biofilm formation, increased susceptibility to antimicrobials and hydrogen peroxide-induced oxidative stress, and decreased internalization by macrophages. This study shows that Mycma_0076 ferritin in Mycma is involved in resistance to oxidative stress and antimicrobials, and alteration of cell envelope architecture. KEY POINTS: • Deletion of the mycma_0076 gene altered colony morphology to rough; • Mycma 0076KO changed GPL profile; • Absence of Mycma_0076 ferritin results in increased susceptibility to antimicrobials and oxidative stress in Mycma. Legend: a In wild-type M. abscessus subsp. massiliense strain, iron is captured from the environment by carboxymycobactins and mycobactins (1). Iron-dependent regulator (IdeR) proteins bind to ferrous iron (Fe⁺²) in the bacterial cytoplasm leading to the activation of the IdeR-Fe⁺² complex (2). The activated complex binds to the promoter regions of iron-dependent genes, called iron box, which in turn help in the recruitment of RNA polymerase to promote transcription of genes such as mycma_0076 and mycma_0077 ferritin genes (3). Mycma_0076 and Mycma_0077 ferritins bind to excess iron in the medium and promote Fe²⁺ oxidation into ferric iron (Fe³⁺) and store iron molecules to be released under iron scarcity conditions. (4) Genes related to biosynthesis and transport of glycopeptidolipids (GPL) are expressed normally and the cell envelope is composed of different GPL species (colored squares represented on the cell surface (GPLs). Consequently, WT Mycma present smooth colony phenotype (5). b In Mycma 0076KO strain, the lack of ferritin 0076 causes overexpression of mycma_0077 (6), but does not restore wild-type iron homeostasis and thus may result in free intracellular iron, even in the presence of miniferritins (MaDps). The excess iron potentiates oxidative stress (7) by generating hydroxyl radicals through Fenton Reaction. During this process, through an unknown mechanism, that could involve Lsr2 (8), the expression of GPL synthesis locus is regulated positively and/or negatively, resulting in alteration of GPL composition in the membrane (as represented by different colors of squares on the cell surface), resulting in a rough colony phenotype (9). The changes of GPL can increase cell wall permeability, contributing to antimicrobial susceptibility (10).

Proteome Profile Changes Induced by Heterologous Overexpression of Mycobacterium tuberculosis-Derived Antigens PstS-1 (Rv0934) and Ag85B (Rv1886c) in Mycobacterium microti

The development of new tuberculosis vaccines remains a global priority, and recombinant vaccines are a frequently investigated option. These vaccines follow a molecular strategy that may enhance protective efficacy. However, their functional differences, particularly with respect to glycosylation, remain unknown. Recent studies have shown that glycosylation plays a key role in the host-pathogen interactions during immune recognition. The aim of this study was to determine the differences in the glycosylation profiles of two recombinant strains of Mycobacterium microti, overexpressing Ag85B (Rv1886c) and PstS-1 (Rv0934) antigens of M. tuberculosis. For each strain, the glycosylation profile was determined by Western blotting with lectins. The results showed the presence of mannosylated proteins and evidence of linked sialic acid proteins. Interestingly, different proteome and glycoproteome profiles were observed between the two recombinant strains and the wild-type strain. We have shown here that the construction of the recombinant strains of M. microti has altered the proteome and glycosylation profiles of these strains, leading us to ask what impact these changes might have on the immune response.

Inhibition of the Niemann-Pick C1 protein is a conserved feature of multiple strains of pathogenic mycobacteria

Mycobacterium tuberculosis (Mtb) survives and replicates within host macrophages (MΦ) and subverts multiple antimicrobial defense mechanisms. Previously, we reported that lipids shed by pathogenic mycobacteria inhibit NPC1, the lysosomal membrane protein deficient in the lysosomal storage disorder Niemann-Pick disease type C (NPC). Inhibition of NPC1 leads to a drop in lysosomal calcium levels, blocking phagosome-lysosome fusion leading to mycobacterial survival. We speculated that the production of specific cell wall lipid(s) that inhibit NPC1 could have been a critical step in the evolution of pathogenicity. We therefore investigated whether lipid extracts from clinical Mtb strains from multiple Mtb lineages, Mtb complex (MTBC) members and non-tubercular mycobacteria (NTM) inhibit the NPC pathway. We report that inhibition of the NPC pathway was present in all clinical isolates from Mtb lineages 1, 2, 3 and 4, Mycobacterium bovis and the NTM, Mycobacterium abscessus and Mycobacterium avium. However, lipid extract from Mycobacterium canettii, which is considered to resemble the common ancestor of the MTBC did not inhibit the NPC1 pathway. We conclude that the evolution of NPC1 inhibitory mycobacterial cell wall lipids evolved early and post divergence from Mycobacterium canettii-related mycobacteria and that this activity contributes significantly to the promotion of disease.

LysX2 is a Mycobacterium tuberculosis membrane protein with an extracytoplasmic MprF-like domain

BACKGROUND

Aminoacyl-phosphatidylglycerol (aaPG) synthases are bacterial enzymes that usually catalyze transfer of aminoacyl residues to the plasma membrane phospholipid phosphatidylglycerol (PG). The result is introduction of positive charges onto the cytoplasmic membrane, yielding reduced affinity towards cationic antimicrobial peptides, and increased resistance to acidic environments. Therefore, these enzymes represent an important defense mechanism for many pathogens, including Staphylococcus aureus and Mycobacterium tuberculosis (Mtb), which are known to encode for lysyl-(Lys)-PG synthase MprF and LysX, respectively. Here, we used a combination of bioinformatic, genetic and bacteriological methods to characterize a protein encoded by the Mtb genome, Rv1619, carrying a domain with high similarity to MprF-like domains, suggesting that this protein could be a new aaPG synthase family member. However, unlike homologous domains of MprF and LysX that are positioned in the cytoplasm, we predicted that the MprF-like domain in LysX2 is in the extracytoplasmic region.

RESULTS

Using genetic fusions to the Escherichia coli proteins PhoA and LacZ of LysX2, we confirmed this unique membrane topology, as well as LysX and MprF as benchmarks. Expression of lysX2 in Mycobacterium smegmatis increased cell resistance to human β-defensin 2 and sodium nitrite, enhanced cell viability and delayed biofilm formation in acidic pH environment. Remarkably, MtLysX2 significantly reduced the negative charge on the bacterial surface upon exposure to an acidic environment. Additionally, we found LysX2 orthologues in major human pathogens and in rapid-growing mycobacteria frequently associated with human infections, but not in environmental and non-pathogenic mycobacteria.

CONCLUSIONS

Overall, our data suggest that LysX2 is a prototype of a new class within the MprF-like protein family that likely enhances survival of the pathogenic species through its catalytic domain which is exposed to the extracytoplasmic side of the cell membrane and is required to decrease the negative charge on the bacterial surface through a yet uncharacterized mechanism.

Glycopeptidolipid glycosylation controls surface properties and pathogenicity in Mycobacterium abscessus

Mycobacterium abscessus is an emerging and difficult-to-manage mycobacterial species that exhibits smooth (S) or rough (R) morphotypes. Disruption of glycopeptidolipid (GPL) production results in transition from S to R and severe lung disease. A structure-activity relationship study was undertaken to decipher the role of GPL glycosylation in morphotype transition and pathogenesis. Deletion of gtf3 uncovered the prominent role of the extra rhamnose in enhancing mannose receptor-mediated internalization of M. abscessus by macrophages. In contrast, the absence of the 6-deoxy-talose and the first rhamnose in mutants lacking gtf1 and gtf2, respectively, affected M abscessus phagocytosis but also resulted in the S-to-R transition. Strikingly, gtf1 and gtf2 mutants displayed a strong propensity to form cords and abscesses in zebrafish, leading to robust and lethal infection. Together, these results underscore the importance and differential contribution of GPL monosaccharides in promoting virulence and infection outcomes.

Mycobacterium tuberculosis modifies cell wall carbohydrates during biofilm growth with a concomitant reduction in complement activation

The development of new vaccines for TB needs to be underpinned by an understanding of both the molecular and cellular mechanisms of host-pathogen interactions and how the immune response can be modulated to achieve protection from disease. Complement orchestrates many aspects of the innate and adaptive immune responses. However, little is known about the contribution of the complement pathways during TB disease, particularly with respect to mycobacterial phenotype. Extracellular communities (biofilms) of M. tuberculosis are found in the acellular rim of granulomas, during disease, and these are likely to be present in post-primary TB episodes, in necrotic lesions. Our study aimed to determine which mycobacterial cell wall components were altered during biofilm growth and how these cell wall alterations modified the complement response. We have shown that M. tuberculosis biofilms modified their cell wall carbohydrates and elicited reduced classical and lectin pathway activation. Consistent with this finding was the reduction of C3b/iC3b deposition on biofilm cell wall carbohydrate extracts. Here, we have highlighted the role of cell wall carbohydrate alterations during biofilm growth of M. tuberculosis and subsequent modulation of complement activation.

The thick waxy coat of mycobacteria, a protective layer against antibiotics and the host's immune system

Tuberculosis, caused by the pathogenic bacterium Mycobacterium tuberculosis (Mtb), is the leading cause of death from an infectious disease, with a mortality rate of over a million people per year. This pathogen's remarkable resilience and infectivity is largely due to its unique waxy cell envelope, 40% of which comprises complex lipids. Therefore, an understanding of the structure and function of the cell wall lipids is of huge indirect clinical significance. This review provides a synopsis of the cell envelope and the major lipids contained within, including structure, biosynthesis and roles in pathogenesis.

O-Methylation of the Glycopeptidolipid Acyl Chain Defines Surface Hydrophobicity of Mycobacterium abscessus and Macrophage Invasion

Mycobacterium abscessus, an emerging pathogen responsible for severe lung infections in cystic fibrosis patients, displays either smooth (S) or rough (R) morphotypes. The S-to-R transition is associated with reduced levels of glycopeptidolipid (GPL) production and is correlated with increased pathogenicity in animal and human hosts. While the structure of GPL is well established, its biosynthetic pathway is incomplete. In addition, the biological functions of the distinct structural parts of this complex lipid remain elusive. Herein, the fmt gene encoding a putative O-methyltransferase was deleted in the M. abscessus S variant. Subsequent biochemical and structural analyses demonstrated that methoxylation of the fatty acyl chain of GPL was abrogated in the Δfmt mutant, and this defect was rescued upon complementation with a functional fmt gene. In contrast, the introduction of fmt derivatives mutated at residues essential for methyltransferase activity failed to complement GPL defects, indicating that fmt encodes an O-methyltransferase. Unexpectedly, phenotypic analyses showed that Δfmt was more hydrophilic than its parental progenitor, as demonstrated by hexadecane-aqueous buffer partitioning and atomic force microscopy experiments with hydrophobic probes. Importantly, the invasion rate of THP-1 macrophages by Δfmt was reduced by 50% when compared to the wild-type strain. Together, these results indicate that Fmt O-methylates the lipid moiety of GPL and plays a substantial role in conditioning the surface hydrophobicity of M. abscessus as well as in the early steps of the interaction between the bacilli and macrophages.

Recombinant O-mannosylated protein production (PstS-1) from Mycobacterium tuberculosis in Pichia pastoris (Komagataella phaffii) as a tool to study tuberculosis infection

Background

Pichia pastoris (syn. Komagataella phaffii) is one of the most highly utilized eukaryotic expression systems for the production of heterologous glycoproteins, being able to perform both N- and O-mannosylation. In this study, we present the expression in P. pastoris of an O-mannosylated recombinant version of the 38 kDa glycolipoprotein PstS-1 from Mycobacterium tuberculosis (Mtb), that is similar in primary structure to the native secreted protein.

Results

The recombinant PstS-1 (rPstS-1) was produced without the native lipidation signal. Glycoprotein expression was under the control of the methanol-inducible promoter pAOX1, with secretion being directed by the α-mating factor secretion signal. Production of rPstS-1 was carried out in baffled shake flasks (BSFs) and controlled bioreactors. A production up to ~ 46 mg/L of the recombinant protein was achieved in both the BSFs and the bioreactors. The recombinant protein was recovered from the supernatant and purified in three steps, achieving a preparation with 98% electrophoretic purity. The primary and secondary structures of the recombinant protein were characterized, as well as its O-mannosylation pattern. Furthermore, a cross-reactivity analysis using serum antibodies from patients with active tuberculosis demonstrated recognition of the recombinant glycoprotein, indirectly indicating the similarity between the recombinant PstS-1 and the native protein from Mtb.

Conclusions

rPstS-1 (98.9% sequence identity, O-mannosylated, and without tags) was produced and secreted by P. pastoris, demonstrating that this yeast is a useful cell factory that could also be used to produce other glycosylated Mtb antigens. The rPstS-1 could be used as a tool for studying the role of this molecule during Mtb infection, and to develop and improve vaccines or kits based on the recombinant protein for serodiagnosis.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1059-3) contains supplementary material, which is available to authorized users.

Two dd-Carboxypeptidases from Mycobacterium smegmatis Affect Cell Surface Properties through Regulation of Peptidoglycan Cross-Linking and Glycopeptidolipids

During the peptidoglycan (PG) maturation of mycobacteria, the glycan strands are interlinked by both 3-3 (between two meso-diaminopimelic acids [meso-DAPs]) and 4-3 cross-links (between d-Ala and meso-DAP), though there is a predominance (60 to 80%) of 3-3 cross-links. The dd-carboxypeptidases (dd-CPases) act on pentapeptides to generate tetrapeptides that are used by ld-transpeptidases as substrates to form 3-3 cross-links. Therefore, dd-CPases play a crucial role in mycobacterial PG cross-link formation. However, the physiology of dd-CPases in mycobacteria is relatively unexplored. In this study, we deleted two dd-CPase genes, msmeg_2433 and msmeg_2432, both individually and in combination, from Mycobacterium smegmatis mc²155. Though the single dd-CPase gene deletions had no significant impact on the mycobacterial physiology, many interesting functional alterations were observed in the double-deletion mutant, viz, a predominance in PG cross-link formation was shifted from 3-3 cross-links to 4-3, cell surface glycopeptidolipid (GPL) expression was reduced, and susceptibility to β-lactams and antitubercular agents was enhanced. Moreover, the survival rate of the double mutant within murine macrophages was higher than that of the parent. Interestingly, the complementation with any one of the dd-CPase genes could restore the wild-type phenotype. In a nutshell, we infer that the altered ratio of 4-3 to 3-3 PG cross-links might have influenced the expression of surface GPLs, colony morphology, biofilm formation, drug susceptibility, and subsistence of the cells within macrophages.IMPORTANCE The glycan strands in mycobacterial peptidoglycan (PG) are interlinked by both 3-3 and 4-3 cross-links. The dd-CPases generate tetrapeptides by acting on the pentapeptides, and ld-transpeptidases use tetrapeptides as substrates to form 3-3 cross-links. In this study, we showed that simultaneous deletions of two dd-CPases alter the nature of PG cross-linking from 3-3 cross-links to 4-3 cross-links. The deletions subsequently decrease the expression of glycopeptidolipids (significant surface lipid present in many nontuberculous mycobacteria, including Mycobacterium smegmatis) and affect other physiological parameters, like cell morphology, growth rate, biofilm formation, antibiotic susceptibility, and survival within murine macrophages. Thus, unraveling the physiology of dd-CPases might help us design antimycobacterial therapeutics in the future.

Glycopeptidolipids, a Double-Edged Sword of the Mycobacterium abscessus Complex

Mycobacterium abscessus is a rapidly-growing species causing a diverse panel of clinical manifestations, ranging from cutaneous infections to severe respiratory disease. Its unique cell wall, contributing largely to drug resistance and to pathogenicity, comprises a vast panoply of complex lipids, among which the glycopeptidolipids (GPLs) have been the focus of intense research. These lipids fulfill various important functions, from sliding motility or biofilm formation to interaction with host cells and intramacrophage trafficking. Being highly immunogenic, the induction of a strong humoral response is likely to select for rough low-GPL producers. These, in contrast to the smooth high-GPL producers, display aggregative properties, which strongly impacts upon intracellular survival. A propensity to grow as extracellular cords allows these low-GPL producing bacilli to escape the innate immune defenses. Transitioning from high-GPL to low-GPL producers implicates mutations within genes involved in biosynthesis or transport of GPL. This leads to induction of an intense pro-inflammatory response and robust and lethal infections in animal models, explaining the presence of rough isolates in patients with decreased pulmonary functions. Herein, we will discuss how, thanks to the generation of defined GPL mutants and the development of appropriate cellular and animal models to study pathogenesis, GPL contribute to M. abscessus biology and physiopathology.

A Simple and Rapid Gene Disruption Strategy in Mycobacterium abscessus: On the Design and Application of Glycopeptidolipid Mutants

Little is known about the disease-causing genetic determinants that are used by Mycobacterium abscessus, increasingly acknowledged as an important emerging pathogen, notably in cystic fibrosis. The presence or absence of surface exposed glycopeptidolipids (GPL) conditions the smooth (S) or rough (R) M. abscessus subsp. abscessus (M. abscessus) variants, respectively, which are characterized by distinct infective programs. However, only a handful of successful gene knock-out and conditional mutants have been reported in M. abscessus, testifying that genetic manipulation of this mycobacterium is difficult. To facilitate gene disruption and generation of conditional mutants in M. abscessus, we have designed a one-step single cross-over system that allows the rapid and simple generation of such mutants. Cloning of as small as 300 bp of the target gene allows for efficient homologous recombination to occur without additional exogenous recombination-promoting factors. The presence of tdTomato on the plasmids allows easily sifting out the large background of mutants spontaneously resistant to antibiotics. Using this strategy in the S genetic background and the target gene mmpL4a, necessary for GPL synthesis and transport, nearly 100% of red fluorescent clones exhibited a rough morphotype and lost GPL on the surface, suggesting that most red fluorescent colonies obtained after transformation incorporated the plasmid through homologous recombination into the chromosome. This system was further exploited to generate another strain with reduced GPL levels to explore how the presence of these cell wall-associated glycolipids influences M. abscessus hydrophobicity as well as virulence in the zebrafish model of infection. This mutant exhibited a more pronounced killing phenotype in zebrafish embryos compared to its S progenitor and this effect correlated with the production of abscesses in the central nervous system. Overall, these results suggest that the near-complete absence of GPL on the bacterial surface is a necessary condition for optimal pathogenesis of this mycobacterium. They also suggest that GPL content affects hydrophobicity of M. abscessus, potentially altering the aerosol transmission, which is of particular importance from an epidemiological and clinical perspective.

The distinct fate of smooth and rough Mycobacterium abscessus variants inside macrophages

Mycobacterium abscessus is a pathogenic, rapidly growing mycobacterium responsible for pulmonary and cutaneous infections in immunocompetent patients and in patients with Mendelian disorders, such as cystic fibrosis (CF). Mycobacterium abscessus is known to transition from a smooth (S) morphotype with cell surface-associated glycopeptidolipids (GPL) to a rough (R) morphotype lacking GPL. Herein, we show that M. abscessus S and R variants are able to grow inside macrophages and are present in morphologically distinct phagosomes. The S forms are found mostly as single bacteria within phagosomes characterized by a tightly apposed phagosomal membrane and the presence of an electron translucent zone (ETZ) surrounding the bacilli. By contrast, infection with the R form leads to phagosomes often containing more than two bacilli, surrounded by a loose phagosomal membrane and lacking the ETZ. In contrast to the R variant, the S variant is capable of restricting intraphagosomal acidification and induces less apoptosis and autophagy. Importantly, the membrane of phagosomes enclosing the S forms showed signs of alteration, such as breaks or partial degradation. Although not frequently encountered, these events suggest that the S form is capable of provoking phagosome-cytosol communication. In conclusion, M. abscessus S exhibits traits inside macrophages that are reminiscent of slow-growing mycobacterial species.

The role of hydrophobicity in tuberculosis evolution and pathogenicity

The evolution of tubercle bacilli parallels a route from environmental Mycobacterium kansasii, through intermediate "Mycobacterium canettii", to the modern Mycobacterium tuberculosis complex. Cell envelope outer membrane lipids change systematically from hydrophilic lipooligosaccharides and phenolic glycolipids to hydrophobic phthiocerol dimycocerosates, di- and pentaacyl trehaloses and sulfoglycolipids. Such lipid changes point to a hydrophobic phenotype for M. tuberculosis sensu stricto. Using Congo Red staining and hexadecane-aqueous buffer partitioning, the hydrophobicity of rough morphology M. tuberculosis and Mycobacterium bovis strains was greater than smooth "M. canettii" and M. kansasii. Killed mycobacteria maintained differential hydrophobicity but defatted cells were similar, indicating that outer membrane lipids govern overall hydrophobicity. A rough M. tuberculosis H37Rv ΔpapA1 sulfoglycolipid-deficient mutant had significantly diminished Congo Red uptake though hexadecane-aqueous buffer partitioning was similar to H37Rv. An M. kansasii, ΔMKAN27435 partially lipooligosaccharide-deficient mutant absorbed marginally more Congo Red dye than the parent strain but was comparable in partition experiments. In evolving from ancestral mycobacteria, related to "M. canettii" and M. kansasii, modern M. tuberculosis probably became more hydrophobic by increasing the proportion of less polar lipids in the outer membrane. Importantly, such a change would enhance the capability for aerosol transmission, affecting virulence and pathogenicity.

Inactivation of MSMEG_0412 gene drastically affects surface related properties of Mycobacterium smegmatis

Background

The outermost layer of mycobacterial cell wall is rich in lipids and glycolipids, surface molecules which differ among species. Mycobacterium smegmatis, an attractive model for the study of both pathogenic and non-pathogenic mycobacteria, presents glycopeptidolipids (GPLs). All the genes necessary for the biosynthesis of such molecules are clustered in a single region of 65 kb and among them, the msmeg_0412 gene has not been characterized yet. Here we report the isolation and subsequent analysis of a MSMEG_0412 null mutant strain.

Results

The inactivation of the msmeg_0412 gene had a drastic impact on bacterial surface properties which resulted in the lack of sliding motility, altered biofilm formation and enhanced drug susceptibility. The GPLs analysis showed that the observed mutant phenotype was due to GPLs deficiencies on the mycobacterial cell wall. In addition, we report that the expression of the gene is enhanced in the presence of lipidic substrates and that the encoded protein has a membrane localization.

Conclusion

msmeg_0412 plays a crucial role for GPLs production and translocation on M. smegmatis surface. Its deletion alters the surface properties and the antibiotic permeability of the mycobacterial cell barrier.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0888-z) contains supplementary material, which is available to authorized users.

Mycobacteria Clumping Increase Their Capacity to Damage Macrophages

The rough morphotypes of non-tuberculous mycobacteria have been associated with the most severe illnesses in humans. This idea is consistent with the fact that Mycobacterium tuberculosis presents a stable rough morphotype. Unlike smooth morphotypes, the bacilli of rough morphotypes grow close together, leaving no spaces among them and forming large aggregates (clumps). Currently, the initial interaction of macrophages with clumps remains unclear. Thus, we infected J774 macrophages with bacterial suspensions of rough morphotypes of M. abscessus containing clumps and suspensions of smooth morphotypes, primarily containing isolated bacilli. Using confocal laser scanning microscopy and electron microscopy, we observed clumps of at least five rough-morphotype bacilli inside the phagocytic vesicles of macrophages at 3 h post-infection. These clumps grew within the phagocytic vesicles, killing 100% of the macrophages at 72 h post-infection, whereas the proliferation of macrophages infected with smooth morphotypes remained unaltered at 96 h post-infection. Thus, macrophages phagocytose large clumps, exceeding the bactericidal capacities of these cells. Furthermore, proinflammatory cytokines and granuloma-like structures were only produced by macrophages infected with rough morphotypes. Thus, the present study provides a foundation for further studies that consider mycobacterial clumps as virulence factors.

Genetics of Capsular Polysaccharides and Cell Envelope (Glyco)lipids

This article summarizes what is currently known of the structures, physiological roles, involvement in pathogenicity, and biogenesis of a variety of noncovalently bound cell envelope lipids and glycoconjugates of Mycobacterium tuberculosis and other Mycobacterium species. Topics addressed in this article include phospholipids; phosphatidylinositol mannosides; triglycerides; isoprenoids and related compounds (polyprenyl phosphate, menaquinones, carotenoids, noncarotenoid cyclic isoprenoids); acyltrehaloses (lipooligosaccharides, trehalose mono- and di-mycolates, sulfolipids, di- and poly-acyltrehaloses); mannosyl-beta-1-phosphomycoketides; glycopeptidolipids; phthiocerol dimycocerosates, para-hydroxybenzoic acids, and phenolic glycolipids; mycobactins; mycolactones; and capsular polysaccharides.

Subinhibitory Doses of Aminoglycoside Antibiotics Induce Changes in the Phenotype of Mycobacterium abscessus

Subinhibitory doses of antibiotics have been shown to cause changes in bacterial morphology, adherence ability, and resistance to antibiotics. In this study, the effects of subinhibitory doses of aminoglycoside antibiotics on Mycobacterium abscessus were investigated. The treatment of M. abscessus cells with subinhibitory doses of amikacin was found to change their colony from a smooth to a rough morphotype and increase their ability to adhere to a polyvinylchloride plate, aggregate in culture, and resist phagocytosis and killing by macrophages. M. abscessus cells treated with a subinhibitory dose of amikacin also became more potent in Toll-like receptor 2 (TLR-2) stimulation, leading to increased tumor necrosis factor alpha (TNF-α) production by macrophages. The MAB_3508c gene was shown to play a role in mediating these phenotypic changes, as its expression in M. abscessus cells was increased when they were treated with a subinhibitory dose of amikacin. In addition, overexpression of MAB_3508c in M. abscessus cells caused changes similar to those induced by subinhibitory doses of amikacin, including a switch from smooth to rough colony morphology, increased ability to aggregate in liquid culture, decreased motility, and increased resistance to killing by macrophages. These findings suggest the importance of using sufficient doses of antibiotics for the treatment of M. abscessus infections.

The molecular biology of mycobacterial trehalose in the quest for advanced tuberculosis therapies

Trehalose is a natural glucose disaccharide identified in the 19th century in fungi and insect cocoons, and later across the three domains of life. In members of the genus Mycobacterium, which includes the tuberculosis (TB) pathogen and over 160 species of nontuberculous mycobacteria (NTM), many of which are opportunistic pathogens, trehalose has been an important focus of research over the last 60 years. It is a crucial player in the assembly and architecture of the remarkable mycobacterial cell envelope as an element of unique highly antigenic glycolipids, namely trehalose dimycolate ('cord factor'). Free trehalose has been detected in the mycobacterial cytoplasm and occasionally in oligosaccharides with unknown function. TB and NTM infection statistics and death toll, the decline in immune responses in the aging population, human immunodeficiency virus/AIDS or other debilitating conditions, and the proliferation of strains with different levels of resistance to the dated drugs in use, all merge into a serious public-health threat urging more effective vaccines, efficient diagnostic tools and new drugs. This review deals with the latest findings on mycobacterial trehalose biosynthesis, catabolism, processing and recycling, as well with the ongoing quest for novel trehalose-related mechanisms to be targeted by novel TB therapeutics. In this context, the drug-discovery pipeline has recently included new lead compounds directed toward trehalose-related targets highlighting the potential of these pathways to stem the tide of rising drug resistance.

Genome analysis reveals three genomospecies in Mycobacterium abscessus

Background

Mycobacterium abscessus complex, the third most frequent mycobacterial complex responsible for community- and health care-associated infections in developed countries, comprises of M. abscessus subsp. abscessus and M. abscessus subsp. bolletii reviously referred as Mycobacterium bolletii and Mycobacterium massiliense. The diversity of this group of opportunistic pathogens is poorly described.

Results

In-depth analysis of 14 published M. abscessus complex genomes found a pan-genome of 6,153 proteins and core-genome of 3,947 (64.1%) proteins, indicating a non-conservative genome. Analysing the average percentage of amino-acid sequence identity (from 94.19% to 98.58%) discriminates three main clusters C1, C2 and C3: C1 comprises strains belonging to M. abscessus, C2 comprises strains belonging to M. massiliense and C3 comprises strains belonging to M. bolletii; and two sub-clusters in clusters C2 and C3. The phylogenomic network confirms these three clusters. The genome length (from 4.8 to 5.51-Mb) varies from 5.07-Mb in C1, 4.89-Mb in C2A, 5.01-Mb in C2B and 5.28-Mb in C3. The mean number of prophage regions (from 0 to 7) is 2 in C1; 1.33 in C2A; 3.5 in C2B and five in C3. A total of 36 genes are uniquely present in C1, 15 in C2 and 15 in C3. These genes could be used for the detection and identification of organisms in each cluster. Further, the mean number of host-interaction factors (including PE, PPE, LpqH, MCE, Yrbe and type VII secretion system ESX3 and ESX4) varies from 70 in cluster C1, 80 in cluster C2A, 74 in cluster C2B and 93 in clusters C3A and C3B. No significant differences in antibiotic resistance genes were observed between clusters, in contrast to previously reported in-vitro patterns of drug resistance. They encode both penicillin-binding proteins targeted by β-lactam antibiotics and an Ambler class A β-lactamase for which inhibitors exist.

Conclusions

Our comparative analysis indicates that M. abscessus complex comprises three genomospecies, corresponding to M. abscessus, M. bolletii, and M. massiliense. The genomics data here reported indicate differences in virulence of medical interest; and suggest targets for the refined detection and identification of M. abscessus.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-359) contains supplementary material, which is available to authorized users.

Increased phagocytosis of Mycobacterium marinum mutants defective in lipooligosaccharide production: a structure-activity relationship study

Mycobacterium marinum is a waterborne pathogen responsible for tuberculosis-like infections in ectotherms and is an occasional opportunistic human pathogen. In the environment, M. marinum also interacts with amoebae, which may serve as a natural reservoir for this microorganism. However, the description of mycobacterial determinants in the early interaction with macrophages or amoebae remains elusive. Lipooligosaccharides (LOSs) are cell surface-exposed glycolipids capable of modulating the host immune system, suggesting that they may be involved in the early interactions of M. marinum with macrophages. Herein, we addressed whether LOS composition affects the uptake of M. marinum by professional phagocytes. Mutants with various truncated LOS variants were generated, leading to the identification of several previously uncharacterized biosynthetic genes (wbbL2, MMAR_2321, and MMAR_2331). Biochemical and structural approaches allowed resolving the structures of LOS precursors accumulating in this set of mutants. These strains with structurally defined LOS profiles were then used to infect both macrophages and Acanthamoebae. An inverse correlation between LOS completeness and uptake of mycobacteria by phagocytes was found, allowing the proposal of three mutant classes: class I (papA4), devoid of LOS and highly efficiently phagocytosed; class II, accumulating only early LOS intermediates (wbbL2 and MMAR_2331) and efficiently phagocytosed but less than class I mutants; class III, lacking LOS-IV (losA, MMAR_2319, and MMAR_2321) and phagocytosed similarly to the control strain. These results indicate that phagocytosis is conditioned by the LOS pattern and that the LOS pathway used by M. marinum in macrophages is conserved during infection of amoebae.

Structure and function of mycobacterium glycopeptidolipids from comparative genomics perspective

Glycopeptidolipids (GPLs) attached to the outer surface of the greasy cell envelope, are a class of important glycolipids synthesized by several non-tuberculosis mycobacteria. The deletion or structure change of GPLs confers several phenotypical changes including colony morphology, hydrophobicity, aggregation, sliding motility, and biofilm formation. In addition, GPLs, particular serovar specific GPLs, are important immunomodulators. This review aims to summarize the advance on the structure, function and biosynthesis of mycobacterium GPLs.

Structural determination of glycopeptidolipids of Mycobacterium smegmatis by high-resolution multiple-stage linear ion-trap mass spectrometry with electrospray ionization

Glycopeptidolipids (GPLs) are abundant in the cell walls of different species of mycobacteria and consist of tripeptide-amino-alcohol core of D-Phe-D-allo-Thr-D-Ala-L-alaninol linked to 3-hydroxy or 3-methoxy C(26-34) fatty acyl chain at the N-terminal of D-Phe via amide linkage, and a 6-deoxytalose (6-dTal) and an O-methyl rhamnose residues, respectively, attach to D-allo-Thr and the terminal L-alaninol. They are important cell-surface antigens that are implicated in the pathogenesis of opportunistic mycobacteria belonging to the Mycobacterium avium complex. In this contribution, we described multiple-stage linear ion trap in conjunction with high-resolution mass spectrometry towards structural characterization of complex GPLs as [M + Na](+) ions isolated from Mycobacterium smegmatis, a fast-growing and non-pathogenic mycobacterial species. Following resonance excitation in an ion trap, MS(n) spectra of the [M + Na](+) ions of GPLs contained mainly b and y series ions that readily determine the peptide sequence. Fragment ions from MS(n) also afford locating the 6-dTal and O-methyl rhamnose residues linked to the D-allo-Thr and terminal L-alaninol of the peptide core, respectively, as well as recognizing the modifications of the glycosides, including their acetylation and methylation states and the presence of succinyl group. The GPL families consisting of 3-hydroxy fatty acyl and of 3-methoxy fatty acyl substituents are readily distinguishable. The MS profiles of the GPLs from cells are dependant on the conditions they were grown, and several isobaric isomers were identified for many of the molecular species. These multiple-stage mass spectrometric approaches give detailed structures of GPL in complex mixtures of which the isomeric structures are difficult to define using other analytical methods.

Retrobiosynthetic approach delineates the biosynthetic pathway and the structure of the acyl chain of mycobacterial glycopeptidolipids

Glycopeptidolipids (GPLs) are dominant cell surface molecules present in several non-tuberculous and opportunistic mycobacterial species. GPLs from Mycobacterium smegmatis are composed of a lipopeptide core unit consisting of a modified C(26)-C(34) fatty acyl chain that is linked to a tetrapeptide (Phe-Thr-Ala-alaninol). The hydroxyl groups of threonine and terminal alaninol are further modified by glycosylations. Although chemical structures have been reported for 16 GPLs from diverse mycobacteria, there is still ambiguity in identifying the exact position of the hydroxyl group on the fatty acyl chain. Moreover, the enzymes involved in the biosynthesis of the fatty acyl component are unknown. In this study we show that a bimodular polyketide synthase in conjunction with a fatty acyl-AMP ligase dictates the synthesis of fatty acyl chain of GPL. Based on genetic, biochemical, and structural investigations, we determine that the hydroxyl group is present at the C-5 position of the fatty acyl component. Our retrobiosynthetic approach has provided a means to understand the biosynthesis of GPLs and also resolve the long-standing debate on the accurate structure of mycobacterial GPLs.

Production of mycobacterial cell wall glycopeptidolipids requires a member of the MbtH-like protein family

Background

Glycopeptidolipids (GPLs) are among the major free glycolipid components of the outer membrane of several saprophytic and clinically-relevant Mycobacterium species. The architecture of GPLs is based on a constant tripeptide-amino alcohol core of nonribosomal peptide synthetase origin that is N-acylated with a 3-hydroxy/methoxy acyl chain synthesized by a polyketide synthase and further decorated with variable glycosylation patterns built from methylated and acetylated sugars. GPLs have been implicated in many aspects of mycobacterial biology, thus highlighting the significance of gaining an understanding of their biosynthesis. Our bioinformatics analysis revealed that every GPL biosynthetic gene cluster known to date contains a gene (referred herein to as gplH) encoding a member of the MbtH-like protein family. Herein, we sought to conclusively establish whether gplH was required for GPL production.

Results

Deletion of gplH, a gene clustered with nonribosomal peptide synthetase-encoding genes in the GPL biosynthetic gene cluster of Mycobacterium smegmatis, produced a GPL deficient mutant. Transformation of this mutant with a plasmid expressing gplH restored GPL production. Complementation was also achieved by plasmid-based constitutive expression of mbtH, a paralog of gplH found in the biosynthetic gene cluster for production of the siderophore mycobactin of M. smegmatis. Further characterization of the gplH mutant indicated that it also displayed atypical colony morphology, lack of sliding motility, altered capacity for biofilm formation, and increased drug susceptibility.

Conclusions

Herein, we provide evidence formally establishing that gplH is essential for GPL production in M. smegmatis. Inactivation of gplH also leads to a pleiotropic phenotype likely to arise from alterations in the cell envelope due to the lack of GPLs. While genes encoding MbtH-like proteins have been shown to be needed for production of siderophores and antibiotics, our study presents the first case of one such gene proven to be required for production of a cell wall component. Furthermore, our results provide the first example of a mbtH-like gene with confirmed functional role in a member of the Mycobacterium genus. Altogether, our findings demonstrate a critical role of gplH in mycobacterial biology and advance our understanding of the genetic requirements for the biosynthesis of an important group of constituents of the mycobacterial outer membrane.

Glycopeptidolipids: immuno-modulators in greasy mycobacterial cell envelope

Species of opportunistic mycobacteria are the major causative agent for disseminating pulmonary infections in immuno-compromised individuals. These naturally resistant strains recruit a unique type of glycolipid known as glycopeptidolipids (GPLs), noncovalently attached to the outer surface of their thick lipid rich cell envelope. Species specific GPLs constitute the chemical determinants of most nontuberculous mycobacterial serotypes, and their absence from the cell surface confers altered colony morphology, hydrophobicity, and inability to grow as biofilms. The objective of this review is to present a comprehensive account and highlight the renewed interest on this much neglected group of pleiotropic molecules with respect to their structural diversity and biosynthesis. In addition, the role of GPLs in mycobacterial survival, both intracellular and in the environment is also discussed. It also explores the possibility of identifying new targets for intervening Mycobacterium avium complex-related infections. These antigenic molecules have been considered to play a pivotal role in immune suppression and can also induce various cytokine mediated innate immune responses, the molecular mechanism of which remains obscure.

Characteristics of Mycobacterium smegmatis J15cs strain lipids

Mycobacterium smegmatis is a rapidly growing, non-pathogenic mycobacterium, and M. smegmatis strain mc(2)155 in particular has been used as a tool for molecular analysis of mycobacteria because of its high rate of transformation. We examined another strain, M. smegmatis J15cs, which has the advantage of surviving for six days in murine macrophages. The J15cs strain produces a rough dry colony, and we hypothesized that the long survival of the J15cs strain was correlated with its cell wall components. Therefore, the lipid compositions of these two strains were compared. The subclasses and carbon species of the mycolic acids were very similar, and the major glycolipids and phospholipids were expressed in both strains. However, apolar glycopeptidolipids were deleted only in the J15cs strain. The presence of apolar glycopeptidolipids gives the cell wall a different structure. Moreover, the apolar glycopeptidolipids were recognized by macrophages via toll-like receptor 2, but not 4. We concluded that the absence of apolar glycopeptidolipids is a definitive feature of the J15cs strain, and affects its morphology and survival in host cells.

Overexpression of proinflammatory TLR-2-signalling lipoproteins in hypervirulent mycobacterial variants

Changes in the cell envelope composition of mycobacteria cause major changes in cytokine profiles of infected antigen presenting cells. We describe here the modulation of inflammatory responses by Mycobacterium abscessus, an emerging pathogen in cystic fibrosis. M. abscessus is able to switch from a smooth (S) to a rough (R) morphotype by the loss of a surface glycopeptidolipid. R variants are associated with severe clinical forms and a 'hyper-proinflammatory' response in ex vivo and in vivo models. Using partitioning of cell surface components we found that a complex fraction, more abundant in R variants than in S variants, made a major contribution to the TLR-2-dependent hyper-proinflammatory response induced by R variants. Lipoproteins were the main TLR-2 agonists in this fraction, consistent with the larger amounts of 16 lipoproteins in cell surface extracts from R variants; 15 out of 16 being more strongly induced in R variant than in S variant. Genetic interruption of glycopeptidolipid pathway in wild-type S variant resulted in R phenotype with similar induction of lipoprotein genes. In conclusion, R morphotype in M. abscessus is associated with increased synthesis/exposure at the cell surface of lipoproteins, these changes profoundly modifying the innate immune response through TLR-2-dependent mechanisms.

Genetic manipulation of Mycobacterium abscessus

This unit covers genetic manipulation protocols for M. abscessus, including nucleic acid extraction (plasmid DNA, genomic DNA, and RNA), transformation, and a recombineering mutagenesis method. M. abscessus is a Biosafety Level 2 (BSL-2) bacterium, and working considerations are also discussed.

A monoacylglycerol lipase from Mycobacterium smegmatis Involved in bacterial cell interaction

MSMEG_0220 from Mycobacterium smegmatis, the ortholog of the Rv0183 gene from M. tuberculosis, recently identified and characterized as encoding a monoacylglycerol lipase, was cloned and expressed in Escherichia coli. The recombinant protein (rMSMEG_0220), which exhibits 68% amino acid sequence identity with Rv0183, showed the same substrate specificity and similar patterns of pH-dependent activity and stability as the M. tuberculosis enzyme. rMSMEG_0220 was found to hydrolyze long-chain monoacylglycerol with a specific activity of 143 +/- 6 U mg(-1). Like Rv0183 in M. tuberculosis, MSMEG_0220 was found to be located in the cell wall. To assess the in vivo role of the homologous proteins, an MSMEG_0220 disrupted mutant of M. smegmatis (MsDelta0220) was produced. An intriguing change in the colony morphology and in the cell interaction, which were partly restored in the complemented mutant containing either an active (ComMsDelta0220) or an inactive (ComMsDelta0220S111A) enzyme, was observed. Growth studies performed in media supplemented with monoolein showed that the ability of both MsDelta0220 and ComMsDelta0220S111A to grow in the presence of this lipid was impaired. Moreover, studies of the antimicrobial susceptibility of the MsDelta0220 strain showed that this mutant is more sensitive to rifampin and more resistant to isoniazid than the wild-type strain, pointing to a critical structural role of this enzyme in mycobacterial physiology, in addition to its function in the hydrolysis of exogenous lipids.

Mycobacterium abscessus: a new player in the mycobacterial field

Mycobacterium abscessus, a relative of Koch's bacillus (the bacterium that causes tuberculosis), has recently emerged as the cause of an increasing number of both community- and hospital-acquired infections in humans; it also constitutes a serious threat for cystic fibrosis patients. This situation is worsened by its exceptionally high natural and acquired antibiotic resistance that complicates treatment. Although a rapid grower, it shares some traits with Koch's bacillus, including the ability to induce a persistent lung disease associated with caseous lesions, a landmark of Mycobacterium tuberculosis infection. Its genome sequence and microarrays are now available, and efficient genetic tools have recently been developed. Here we consider the various advantages of using this species as an experimental model to study tuberculosis and other related mycobacterial diseases.

Downregulation of protein kinase C-alpha enhances intracellular survival of Mycobacteria: role of PknG

Background

Intracellular trafficking of mycobacteria is comprehensively dependent on the unusual regulation of host proteins. Recently, we have reported that infection of macrophages by Mycobacterium tuberculosis H37Rv (Rv) selectively downregulates the expression of PKCα while infection by Mycobacterium smegmatis (MS) does not.

Results

Based on our earlier study, we have extrapolated for the first time that knockdown of PKCα, impairs phagocytosis of mycobacteria by macrophages while their intracellular survival is drastically increased. Mycobacterium bovis BCG (BCG) and Mycobacterium tuberculosis H37Ra (Ra) have also been shown to downregulate the expression of PKCα during the infection. Since PknG is uniquely expressed in BCG, Ra, Rv but not in MS and has been reported to promote intracellular survival of mycobacteria, led us to believe that PknG may be involved in such downregulation of PKCα. THP-1 cells infected with recombinant MS expressing PknG (MS-G), showed significant reduction in PKCα expression. In normal THP-1 cells survival of MS-G was enhanced as compared to MS, while their behavior in PKCα deficient cells could not be distinguished. The results strongly demonstrate that pathogenic mycobacteria recognize and then inhibit PKCα to circumvent phagocytosis and the hostile environment of macrophages. We emphasize that, this inhibition is controlled by PknG.

Conclusions

All together, our data reveal a mechanism that shows substantial interdependence of PKCα with PknG, in sustaining mycobacterial infection.

Lipid profiling using two-dimensional heteronuclear single quantum coherence NMR

The use of NMR spectroscopy in lipid research has been traditionally reserved for the analysis and structural elucidation of discrete lipid molecules. Although NMR analysis of organic molecules provides a plethora of structural information that is normally unattainable by most other techniques, its use for global analysis of mixed lipid pools has been hampered by its relatively low sensitivity and overlapping of signals in the spectrum. However, the last few decades have witnessed great advancements in NMR spectroscopy that generally resulted in greater sensitivity and offered more flexibility in sampling techniques. The method discussed in this chapter describes the use of NMR for global lipidome analysis. This methodology benefits from the quantitative nature of this technique together with the abundance of the structural information it can offer, while partially overcoming the problems of low sensitivity and overlapping signals through isotope-enrichment and the use of multidimensional NMR, respectively. We have applied this method successfully to the mycobacterial lipidome as an example of an organism with a very complex and chemically diverse lipid pool. The same concept is applicable to a wide range of prokaryotes that can grow in the laboratory in well-defined growth media.

Mycobacterium tuberculosis Cpn60.2 and DnaK are located on the bacterial surface, where Cpn60.2 facilitates efficient bacterial association with macrophages

Mycobacterium tuberculosis, the causative agent of tuberculosis, initially contacts host cells with elements of its outer cell wall, or capsule. We have shown that capsular material from the surface of M. tuberculosis competitively inhibits the nonopsonic binding of whole M. tuberculosis bacilli to macrophages in a dose-dependent manner that is not acting through a global inhibition of macrophage binding. We have further demonstrated that isolated M. tuberculosis capsular proteins mediate a major part of this inhibition. Two-dimensional polyacrylamide gel electrophoresis analysis of the capsular proteins showed the presence of a wide variety of protein species, including proportionately high levels of the Cpn60.2 (Hsp65, GroEL2) and DnaK (Hsp70) molecular chaperones. Both of these proteins were subsequently detected on the bacterial surface. To determine whether these molecular chaperones play a role in bacterial binding, recombinant Cpn60.2 and DnaK were tested for their ability to inhibit the association of M. tuberculosis bacilli with macrophages. We found that recombinant Cpn60.2 can inhibit approximately 57% of bacterial association with macrophages, while DnaK was not inhibitory at comparable concentrations. Additionally, when polyclonal F(ab')(2) fragments of anti-Cpn60.2 and anti-DnaK were used to mask the surface presentation of these molecular chaperones, a binding reduction of approximately 34% was seen for anti-Cpn60.2 F(ab')(2), while anti-DnaK F(ab')(2) did not significantly reduce bacterial association with macrophages. Thus, our findings suggest that while M. tuberculosis displays both surface-associated Cpn60.2 and DnaK, only Cpn60.2 demonstrates adhesin functionality with regard to macrophage interaction.

Identification of the polyketide synthase involved in the biosynthesis of the surface-exposed lipooligosaccharides in mycobacteria

Lipooligosaccharides (LOS) are highly antigenic glycolipids produced by a number of Mycobacterium species, which include "M. canettii," a member of the M. tuberculosis complex, and the opportunistic pathogens M. marinum and M. kansasii. The various LOS share a core composed of trehalose esterified by at least 1 mole of polymethyl-branched fatty acid (PMB-FA) and differ from one another by their oligosaccharide extensions. In this study, we identified a cluster of genes, MSMEG_4727 through MSMEG_4741, likely involved in the synthesis of LOS in M. smegmatis. Disruption of MSMEG_4727 (the ortholog of pks5 of M. tuberculosis), which encodes a putative polyketide synthase, resulted in the concomitant abrogation of the production of both PMB-FA and LOS in the mutant strain. Complementation of the mutant with the wild-type gene fully restored the phenotype. We also showed that, in contrast to the case for "M. canettii" and M. marinum, LOS are located in deeper compartments of the cell envelope of M. smegmatis. The availability of two mycobacterial strains differing only in LOS production should help in defining the biological role(s) of this important glycolipid.

Construction of Mycobacterium abscessus defined glycopeptidolipid mutants: comparison of genetic tools

Mycobacterium abscessus is a rapidly growing mycobacterial species that can be involved in pulmonary and disseminated infections in immunosuppressed or young cystic fibrosis patients. It is an emerging pathogen and has attracted recent attention due to the numerous cases of infection; furthermore, genomic tools have been developed for this species. Nevertheless, the study of this species has until now been limited to spontaneous variants. We report here a comparison of three different mutagenesis systems--the ts-sacB, the phage, and the recombineering systems--and show that there are important differences in their efficiency for the construction of allelic-exchange mutants. We show, using the mmpL4b gene of the glycopeptidolipid pathway as a target, that allelic-exchange mutants can be constructed with a reasonable efficiency (approximately 7%) using the recombineering system. These observations will facilitate genetic and cellular microbiology experiments involving the construction and use of well-defined mutants to study the virulence determinant of this emerging pathogen.

Nonionic detergent phase extraction for the proteomic analysis of heart membrane proteins using label-free LC-MS

Heart diseases resulting in heart failure are among the leading causes of morbidity and mortality in the Western world and can result from either systemic disease (e.g., hypertensive heart disease, ischemic heart disease) or specific heart muscle disease (e.g., dilated cardiomyopathy/DCM). Subproteome analysis of such disease subsets affords a reduction in sample complexity, potentially revealing biomarkers of cardiac failure that would otherwise remain undiscovered in proteome wide studies. Label-free nanoscale LC-MS has been applied in this study to validate a Triton X-114-based phase enrichment method for cardiac membrane proteins. Annotation of the subcellular location combined with GRAVY score analysis indicates a clear separation between soluble and membrane-bound proteins with an enrichment of over 62% for this protein subset. LC-MS allowed confident identification and annotation of hydrophobic proteins in this control sample pilot study and demonstrates the power of the proposed technique to extract integral membrane-bound proteins. This approach should be applicable to a wider scale study of disease-associated changes in the cardiac membrane subproteome.

Mycobacterium avium glycopeptidolipids require specific acetylation and methylation patterns for signaling through toll-like receptor 2

Toll-like receptors (TLRs) recognize pathogen-associated molecules and play a vital role in promoting an immune response against invading microbes. TLR2, one of the key members of the TLR family, recognizes a wide variety of microbial products, including lipoproteins and lipopeptides, from a number of pathogens. Recent studies from our laboratory indicate that glycopeptidolipids (GPLs), a major surface component of Mycobacterium avium and other non-tuberculosis mycobacteria, are ligands for TLR2. However, the molecular requirements necessary for the GPL-TLR2 interaction were not defined in this report. In the present study we isolated different GPL species from M. avium, and using mass spectrometry and NMR analyses, characterized the molecular requirements of the GPL-TLR2 interaction. Interestingly, the extent of the respective acetylation and methylation of the 6-deoxytalose and rhamnose contained within the core GPL structure dictated whether the GPL signaled through TLR2. These experiments illustrate how subtle changes in a complex TLR2 ligand can alter its affinity for this important receptor, and suggest that M. avium could potentially modify its GPL structure to limit its interaction with TLR2.

The mycobacterial glycopeptidolipids: structure, function, and their role in pathogenesis

Glycopeptidolipids (GPLs) are a class of glycolipids produced by several nontuberculosis-causing members of the Mycobacterium genus including pathogenic and nonpathogenic species. GPLs are expressed in different forms with production of highly antigenic, typeable serovar-specific GPLs in members of the Mycobacterium avium complex (MAC). M. avium and M. intracellulare, which comprise this complex, are slow-growing mycobacteria noted for producing disseminated infections in AIDS patients and pulmonary infections in non-AIDS patients. Previous studies have defined the gene cluster responsible for GPL biosynthesis and more recent work has characterized the function of the individual genes. Current research has also focused on the GPL's role in colony morphology, sliding motility, biofilm formation, immune modulation and virulence. These topics, along with new information on the enzymes involved in GPL biosynthesis, are the subject of this review.

Spontaneous transposition of IS1096 or ISMsm3 leads to glycopeptidolipid overproduction and affects surface properties in Mycobacterium smegmatis

Natural modification of the colony appearance is a phenomenon that has not been fully understood in mycobacteria. Here, we show that Mycobacterium smegmatis ATCC607 displays a low-frequency spontaneous morphological variation that correlates with the acquisition of a panel of new phenotypes, such as aggregation, biofilm formation and sliding motility. These variants produce larger amounts of glycopeptidolipid (GPL), a cell-surface component, than did the wild-type strain. This conversion results from the transposition of two types of insertion sequences, IS1096 and ISMsm3, into two loci. One locus is the promoter region of the mps operon, the GPL biosynthesis gene cluster, leading to the overexpression of these genes. The other locus is the lsr2 gene, which encodes a small basic histone-like protein that likely plays a regulatory role at the mps promoter and also controls pigment production. This study demonstrates that insertion sequence mobility play a crucial role in the acquisition of new phenotypes.