Gene_locus Report for: myctu-RV3452

Mycobacterium bovis is the causative agent of tuberculosis in a range of animal species and man, with worldwide annual losses to agriculture of $3 billion. The human burden of tuberculosis caused by the bovine tubercle bacillus is still largely unknown. M. bovis was also the progenitor for the M. bovis bacillus Calmette-Guerin vaccine strain, the most widely used human vaccine. Here we describe the 4,345,492-bp genome sequence of M. bovis AF2122/97 and its comparison with the genomes of Mycobacterium tuberculosis and Mycobacterium leprae. Strikingly, the genome sequence of M. bovis is >99.95% identical to that of M. tuberculosis, but deletion of genetic information has led to a reduced genome size. Comparison with M. leprae reveals a number of common gene losses, suggesting the removal of functional redundancy. Cell wall components and secreted proteins show the greatest variation, indicating their potential role in host-bacillus interactions or immune evasion. Furthermore, there are no genes unique to M. bovis, implying that differential gene expression may be the key to the host tropisms of human and bovine bacilli. The genome sequence therefore offers major insight on the evolution, host preference, and pathobiology of M. bovis.

Virulence and immunity are poorly understood in Mycobacterium tuberculosis. We sequenced the complete genome of the M. tuberculosis clinical strain CDC1551 and performed a whole-genome comparison with the laboratory strain H37Rv in order to identify polymorphic sequences with potential relevance to disease pathogenesis, immunity, and evolution. We found large-sequence and single-nucleotide polymorphisms in numerous genes. Polymorphic loci included a phospholipase C, a membrane lipoprotein, members of an adenylate cyclase gene family, and members of the PE/PPE gene family, some of which have been implicated in virulence or the host immune response. Several gene families, including the PE/PPE gene family, also had significantly higher synonymous and nonsynonymous substitution frequencies compared to the genome as a whole. We tested a large sample of M. tuberculosis clinical isolates for a subset of the large-sequence and single-nucleotide polymorphisms and found widespread genetic variability at many of these loci. We performed phylogenetic and epidemiological analysis to investigate the evolutionary relationships among isolates and the origins of specific polymorphic loci. A number of these polymorphisms appear to have occurred multiple times as independent events, suggesting that these changes may be under selective pressure. Together, these results demonstrate that polymorphisms among M. tuberculosis strains are more extensive than initially anticipated, and genetic variation may have an important role in disease pathogenesis and immunity.

Countless millions of people have died from tuberculosis, a chronic infectious disease caused by the tubercle bacillus. The complete genome sequence of the best-characterized strain of Mycobacterium tuberculosis, H37Rv, has been determined and analysed in order to improve our understanding of the biology of this slow-growing pathogen and to help the conception of new prophylactic and therapeutic interventions. The genome comprises 4,411,529 base pairs, contains around 4,000 genes, and has a very high guanine + cytosine content that is reflected in the biased amino-acid content of the proteins. M. tuberculosis differs radically from other bacteria in that a very large portion of its coding capacity is devoted to the production of enzymes involved in lipogenesis and lipolysis, and to two new families of glycine-rich proteins with a repetitive structure that may represent a source of antigenic variation.

The alpha/beta hydrolase fold superfamily is an ancient and widely diversified group of primarily hydrolytic enzymes. In this review, the adaptations of these proteins to the pathogenic lifestyle of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, are examined. Of the 105 alpha/beta hydrolases identified in Mtb, many are associated with lipid metabolism, particularly in the biosynthesis and maintenance of the Mtb's unique cell envelope, as well in the large number of extracellular lipases that are likely responsible for degradation of host lipid material. alpha/beta hydrolase fold proteins are also involved in the evasion and modulation of the immune response, detoxification and metabolic adaptations, including growth, response to acidification of the intracellular environment and dormancy. A striking feature of Mtb's alpha/beta hydrolases is their diversification into virulence-associated niches. It is clear that the alpha/beta hydrolase fold family has made a significant contribution to Mtb's remarkable success as a pathogen.

Chronic tuberculosis in an immunocompetent host is a consequence of the delicately balanced growth of Mycobacterium tuberculosis (Mtb) in the face of host defense mechanisms. We identify an Mtb enzyme (TdmhMtb) that hydrolyzes the mycobacterial glycolipid trehalose dimycolate and plays a critical role in balancing the intracellular growth of the pathogen. TdmhMtb is induced under nutrient-limiting conditions and remodels the Mtb envelope to increase nutrient influx but concomitantly sensitizes Mtb to stresses encountered in the host. Consistent with this, a DeltatdmhMtb mutant is more resilient to stress and grows to levels higher than those of wild-type in immunocompetent mice. By contrast, mutant growth is retarded in MyD88(-/-) mice, indicating that TdmhMtb provides a growth advantage to intracellular Mtb in an immunocompromised host. Thus, the effects and countereffects of TdmhMtb play an important role in balancing intracellular growth of Mtb in a manner that is directly responsive to host innate immunity.

The enzymes belonging to the cutinase family are serine enzymes active on a large panel of substrates such as cutin, triacylglycerols, and phospholipids. In the M. tuberculosis H37Rv genome, seven genes coding for cutinase-like proteins have been identified with strong immunogenic properties suggesting a potential role as vaccine candidates. Two of these enzymes which are secreted and highly homologous, possess distinct substrates specificities. Cfp21 is a lipase and Cut4 is a phospholipase A2, which has cytotoxic effects on macrophages. Structural overlay of their three-dimensional models allowed us to identify three areas involved in the substrate binding process and to shed light on this substrate specificity. By site-directed mutagenesis, residues present in these Cfp21 areas were replaced by residues occurring in Cut4 at the same location. Three mutants acquired phospholipase A1 and A2 activities and the lipase activities of two mutants were 3 and 15 fold greater than the Cfp21 wild type enzyme. In addition, contrary to mutants with enhanced lipase activity, mutants that acquired phospholipase B activities induced macrophage lysis as efficiently as Cut4 which emphasizes the relationship between apparent phospholipase A2 activity and cytotoxicity. Modification of areas involved in substrate specificity, generate recombinant enzymes with higher activity, which may be more immunogenic than the wild type enzymes and could therefore constitute promising candidates for antituberculous vaccine production.

Tuberculosis caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis (MTB) strains is a growing problem in many countries. The availability of the complete nucleotide sequences of several MTB genomes allows to use the comparative genomics as a tool to study the relationships of strains and differences in their evolutionary history including acquisition of drug-resistance. In our work, we sequenced three genomes of Russian MTB strains of different phenotypes--drug susceptible, MDR and XDR. Of them, MDR and XDR strains were collected in Tomsk (Siberia, Russia) during the local TB outbreak in 1998-1999 and belonged to rare KQ and KY families in accordance with IS6110 typing, which are considered endemic for Russia. Based on phylogenetic analysis, our isolates belonged to different genetic families, Beijing, Ural and LAM, which made the direct comparison of their genomes impossible. For this reason we performed their comparison in the broader context of all M. tuberculosis genomes available in GenBank. The list of unique individual non-synonymous SNPs for each sequenced isolate was formed by comparison with all SNPs detected within the same phylogenetic group. For further functional analysis, all proteins with unique SNPs were ascribed to 20 different functional classes based on Clusters of Orthologous Groups (COG). We have confirmed drug resistant status of our isolates that harbored almost all known drug-resistance associated mutations. Unique SNPs of an XDR isolate CTRI-4(XDR), belonging to a Beijing family were compared in more detail with SNPs of additional 14 Russian XDR strains of the same family. Only type specific mutations in genes of repair, replication and recombination system (COG category L) were found common within this group. Probably the other unique SNPs discovered in CTRI-4(XDR) may have an important role in adaptation of this microorganism to its surrounding and in escape from antituberculosis drugs treatment.

Global spread and limited genetic variation are hallmarks of M. tuberculosis, the agent of human tuberculosis. In contrast, Mycobacterium canettii and related tubercle bacilli that also cause human tuberculosis and exhibit unusual smooth colony morphology are restricted to East Africa. Here, we sequenced and analyzed the whole genomes of five representative strains of smooth tubercle bacilli (STB) using Sanger (4-5x coverage), 454/Roche (13-18x coverage) and/or Illumina DNA sequencing (45-105x coverage). We show that STB isolates are highly recombinogenic and evolutionarily early branching, with larger genome sizes, higher rates of genetic variation, fewer molecular scars and distinct CRISPR-Cas systems relative to M. tuberculosis. Despite the differences, all tuberculosis-causing mycobacteria share a highly conserved core genome. Mouse infection experiments showed that STB strains are less persistent and virulent than M. tuberculosis. We conclude that M. tuberculosis emerged from an ancestral STB-like pool of mycobacteria by gain of persistence and virulence mechanisms, and we provide insights into the molecular events involved.

BACKGROUND: With the emergence of next-generation sequencing, the availability of prokaryotic genome sequences is expanding rapidly. A total of 5,276 genomes have been released since 2008, yet only 1,692 genomes were complete. The final phase of microbial genome sequencing, particularly gap closing, is frequently the rate-limiting step either because of complex genomic structures that cause sequence bias even with high genomic coverage, or the presence of repeat sequences that may cause gaps in assembly.
RESULTS: We have developed a Cytoscape plugin to facilitate gap closing for high-throughput sequencing data from microbial genomes. This plugin is capable of interactively displaying the relationships among genomic contigs derived from various sequencing formats. The sequence contigs of plasmids and special repeats (IS elements, ribosomal RNAs, terminal repeats, etc.) can be displayed as well.
CONCLUSIONS: Displaying relationships between contigs using graphs in Cytoscape rather than tables provides a more straightforward visual representation. This will facilitate a faster and more precise determination of the linkages among contigs and greatly improve the efficiency of gap closing.

BACKGROUND: M. africanum West African 2 constitutes an ancient lineage of the M. tuberculosis complex that commonly causes human tuberculosis in West Africa and has an attenuated phenotype relative to M. tuberculosis. METHODOLOGY/PRINCIPAL FINDINGS: In search of candidate genes underlying these differences, the genome of M. africanum West African 2 was sequenced using classical capillary sequencing techniques. Our findings reveal a unique sequence, RD900, that was independently lost during the evolution of two important lineages within the complex: the "modern" M. tuberculosis group and the lineage leading to M. bovis. Closely related to M. bovis and other animal strains within the M. tuberculosis complex, M. africanum West African 2 shares an abundance of pseudogenes with M. bovis but also with M. africanum West African clade 1. Comparison with other strains of the M. tuberculosis complex revealed pseudogenes events in all the known lineages pointing toward ongoing genome erosion likely due to increased genetic drift and relaxed selection linked to serial transmission-bottlenecks and an intracellular lifestyle. CONCLUSIONS/SIGNIFICANCE: The genomic differences identified between M. africanum West African 2 and the other strains of the Mycobacterium tuberculosis complex may explain its attenuated phenotype, and pave the way for targeted experiments to elucidate the phenotypic characteristic of M. africanum. Moreover, availability of the whole genome data allows for verification of conservation of targets used for the next generation of diagnostics and vaccines, in order to ensure similar efficacy in West Africa.

Several genomes of different Mycobacterium tuberculosis isolates have been completely sequenced around the world. The genomic information obtained have shown higher diversity than originally thought and specific adaptations to different human populations. Within this work, we sequenced the genome of one Colombian M. tuberculosis virulent isolate. Genomic comparison against the reference genome of H37Rv and other strains showed multiple deletion and insertions that ranged between a few bases to thousands. Excluding PPE and PG-PGRS genes, 430 proteins present changes in at least 1 amino acid. Also, novel positions of the IS6110 mobile element were identified. This isolate is also characterized by a large genomic deletion of 3.6 kb, leading to the loss and modification of the dosR regulon genes, Rv1996 and Rv1997. To our knowledge, this is the first report of the genome sequence of a Latin American M. tuberculosis clinical isolate.

We report the annotated genome sequence of two clinical isolates of Mycobacterium tuberculosis isolated from Kerala, India.

We report the completely annotated genome sequence of Mycobacterium tuberculosis Erdman (TMC 107; ATCC 35801), which is a well-known laboratory strain of M. tuberculosis.

Mycobacterium bovis bacillus Calmette-Guerin (BCG) is the only vaccine available against tuberculosis, and the strains used worldwide represent a family of daughter strains with distinct genotypic characteristics. Here we report the complete genome sequence of M. bovis BCG Moreau, the strain in continuous use in Brazil for vaccine production since the 1920s.

We report the annotated genome sequence of a clinical isolate, Mycobacterium tuberculosis strain NCGM2209, which belongs to the "Beijing family" and was isolated in Japan.

BACKGROUND: Studies of Mycobacterium bovis BCG strains used in different countries and vaccination programs show clear variations in the genomes and immune protective properties of BCG strains. The aim of this study was to characterise the genomic and immune proteomic profile of the BCG 1931 strain used in Mexico.
RESULTS: BCG Mexico 1931 has a circular chromosome of 4,350,386 bp with a G+C content and numbers of genes and pseudogenes similar to those of BCG Tokyo and BCG Pasteur. BCG Mexico 1931 lacks Region of Difference 1 (RD1), RD2 and N-RD18 and one copy of IS6110, indicating that BCG Mexico 1931 belongs to DU2 group IV within the BCG vaccine genealogy. In addition, this strain contains three new RDs, which are 53 (RDMex01), 655 (RDMex02) and 2,847 bp (REDMex03) long, and 55 single-nucleotide polymorphisms representing non-synonymous mutations compared to BCG Pasteur and BCG Tokyo. In a comparative proteomic analysis, the BCG Mexico 1931, Danish, Phipps and Tokyo strains showed 812, 794, 791 and 701 protein spots, respectively. The same analysis showed that BCG Mexico 1931 shares 62% of its protein spots with the BCG Danish strain, 61% with the BCG Phipps strain and only 48% with the BCG Tokyo strain. Thirty-nine reactive spots were detected in BCG Mexico 1931 using sera from subjects with active tuberculosis infections and positive tuberculin skin tests.
CONCLUSIONS: BCG Mexico 1931 has a smaller genome than the BCG Pasteur and BCG Tokyo strains. Two specific deletions in BCG Mexico 1931 are described (RDMex02 and RDMex03). The loss of RDMex02 (fadD23) is associated with enhanced macrophage binding and RDMex03 contains genes that may be involved in regulatory pathways. We also describe new antigenic proteins for the first time.

Mycobacterium tuberculosis is one of most prevalent pathogens in the world. Drug-resistant strains of this pathogen caused by the excessive use of antibiotics have long posed serious threats to public health worldwide. A broader picture of drug resistance mechanisms at the genomic level can be obtained only with large-scale comparative genomic methodology. Two closely related Beijing family isolates, one resistant to four first-line drugs (CCDC5180) and one sensitive to them (CCDC5079), were completely sequenced. These sequences will serve as valuable references for further drug resistance site identification studies and could be of great importance for developing drugs targeting these sites.

Mycobacterial species, like other microbes, spontaneously form multicellular drug-tolerant biofilms when grown in vitro in detergent-free liquid media. The structure of Mycobacterium tuberculosis biofilms is formed through genetically programmed pathways and is built upon a large abundance of novel extracellular free mycolic acids (FM), although the mechanism of FM synthesis remained unclear. Here we show that the FM in Mycobacterium smegmatis biofilms is produced through the enzymatic release from constitutively present mycolyl derivatives. One of the precursors for FM is newly synthesized trehalose dimycolate (TDM), which is cleaved by a novel TDM-specific serine esterase, Msmeg_1529. Disruption of Msmeg_1529 leads to undetectable hydrolytic activity, reduced levels of FM in the mutant, and retarded biofilm growth. Furthermore, enzymatic hydrolysis of TDM remains conserved in M. tuberculosis, suggesting the presence of a TDM-specific esterase in this pathogen. Overall, this study provides the first evidence for an enzymatic release of free mycolic acids from cell envelope mycolates during mycobacterial growth.

Cutinases are extracellular enzymes that are able to degrade cutin, a polyester protecting plant leaves and many kinds of lipids. Although cutinases are mainly found in phytopathogenic fungi or bacteria, 7 genes related to the cutinase family have been predicted in the genome of Mycobacterium tuberculosis. These genes may encode proteins that are involved in the complex lipid metabolism of the bacterium. Here, we report on the biochemical characterization of two secreted proteins of M. tuberculosis, Rv1984c and Rv3452, belonging to the cutinase family. Although their amino acid sequence shows 50% identity with that of the well-characterized cutinase from Fusarium solani pisi, and a high level of homology has been found to exist between these two enzymes, they show distinct substrate specificities. Rv1984c preferentially hydrolyzes medium-chain carboxylic esters and monoacylglycerols, whereas Rv3452 behaves like a phospholipase A(2), and it is able to induce macrophage lysis. The tetrahydrolipstatin inhibitor, a specific lipase inhibitor, abolishes the activity of both enzymes. Site-directed mutagenesis was performed to identify the catalytic triad of Rv1984c. Structural models for Rv1984c and Rv3452 were built, based on the crystal structure of F. solani cutinase, with a view to investigating the contribution of specific residues to the substrate specificity. Our findings open new prospects for investigating the physiological roles of cutinase-like proteins in the lipid metabolism and virulence of M. tuberculosis.

To investigate the molecular characteristics of bacillus Calmette-Guerin (BCG) vaccines, the complete genomic sequence of Mycobacterium bovis BCG Tokyo 172 was determined, and the results were compared with those for BCG Pasteur and other M. tuberculosis complex. The genome of BCG Tokyo had a length of 4,371,711bp and contained 4033 genes, including 3950 genes coding for proteins (CDS). There were 18 regions of difference (showing differences of more than 20bp), 20 insertion or deletion (ins/del) mutations of less than 20bp, and 68 SNPs between the two BCG substrains. These findings are useful for better understanding of the genetic differences in BCG substrains due to in vitro evolution of BCG.

Discovery and characterization of novel secreted enzymes of Mycobacterium tuberculosis are important for understanding the pathogenesis of one of the most important human bacterial pathogens. The proteome of M. tuberculosis contains over 400 potentially secreted proteins, the majority of which are uncharacterized. A family of seven cutinase-like proteins (CULPs) was identified by bioinformatic analysis, expressed and purified from Escherichia coli, and characterized in terms of their enzymatic activities. These studies revealed a functional diversity of enzyme classes based on differential preferences for substrate chain length. One member, Culp1, exhibited strong esterase activity, 40-fold higher than that of Culp6, which had strong activity as a lipase. Another, Culp4, performed moderately as an esterase and weakly as a lipase. Culp6 lipase activity was optimal above pH 7.0, and fully maintained to pH 8.5. None of the CULP members exhibited cutinase activity. Site-directed mutagenesis of each residue of the putative catalytic triad in Culp6 confirmed that each was essential for activity toward all fatty acid chain lengths of nitrophenyl esters and lipolytic function. Culp1 and Culp2 were present only in culture supernatants of M. tuberculosis, while Culp6, which is putatively essential for mycobacterial growth, was retained in the cell wall, suggesting the proteins play distinct roles in mycobacterial biology.

Secreted proteins of Mycobacterium tuberculosis play key roles in the assembly of the mycobacterial cell wall, with many being major targets of the host immune response. To date, meaningful characterization of a significant proportion of this important group of proteins is lacking. Among the group of putatively secreted proteins of M. tuberculosis are 7 cutinase-like proteins (CLP), not previously characterized in terms of their immunogenicity or vaccine protective efficacy. Although the CLP vary in the degree of homology with one another, they all share a similar active catalytic triad, closely homologous to that of the cutinase of Fusarium solani. By construction of DNA vaccines of all 7 CLP, and expression and purification of soluble, recombinant CLP, this study addresses the immunological responses to these proteins. Clp1, 2, 3 and 6 were found to elicit significant IFN-gamma secretion in DNA immunized mice, with the antigens also demonstrating specificity in terms of CLP-generated T cell IFN-gamma release, with minimal cross reactivity of humoral responses. Finally, following delivery of DNA vaccines, Clp1, 2 and 6, conferred a moderate yet reproducible and significant level of protection in a murine aerosol model of M. tuberculosis infection.

To understand the evolution, attenuation, and variable protective efficacy of bacillus Calmette-Guerin (BCG) vaccines, Mycobacterium bovis BCG Pasteur 1173P2 has been subjected to comparative genome and transcriptome analysis. The 4,374,522-bp genome contains 3,954 protein-coding genes, 58 of which are present in two copies as a result of two independent tandem duplications, DU1 and DU2. DU1 is restricted to BCG Pasteur, although four forms of DU2 exist; DU2-I is confined to early BCG vaccines, like BCG Japan, whereas DU2-III and DU2-IV occur in the late vaccines. The glycerol-3-phosphate dehydrogenase gene, glpD2, is one of only three genes common to all four DU2 variants, implying that BCG requires higher levels of this enzyme to grow on glycerol. Further amplification of the DU2 region is ongoing, even within vaccine preparations used to immunize humans. An evolutionary scheme for BCG vaccines was established by analyzing DU2 and other markers. Lesions in genes encoding sigma-factors and pleiotropic transcriptional regulators, like PhoR and Crp, were also uncovered in various BCG strains; together with gene amplification, these affect gene expression levels, immunogenicity, and, possibly, protection against tuberculosis. Furthermore, the combined findings suggest that early BCG vaccines may even be superior to the later ones that are more widely used.

Mycobacterium bovis is the causative agent of tuberculosis in a range of animal species and man, with worldwide annual losses to agriculture of $3 billion. The human burden of tuberculosis caused by the bovine tubercle bacillus is still largely unknown. M. bovis was also the progenitor for the M. bovis bacillus Calmette-Guerin vaccine strain, the most widely used human vaccine. Here we describe the 4,345,492-bp genome sequence of M. bovis AF2122/97 and its comparison with the genomes of Mycobacterium tuberculosis and Mycobacterium leprae. Strikingly, the genome sequence of M. bovis is >99.95% identical to that of M. tuberculosis, but deletion of genetic information has led to a reduced genome size. Comparison with M. leprae reveals a number of common gene losses, suggesting the removal of functional redundancy. Cell wall components and secreted proteins show the greatest variation, indicating their potential role in host-bacillus interactions or immune evasion. Furthermore, there are no genes unique to M. bovis, implying that differential gene expression may be the key to the host tropisms of human and bovine bacilli. The genome sequence therefore offers major insight on the evolution, host preference, and pathobiology of M. bovis.

Original genome annotations need to be regularly updated if the information they contain is to remain accurate and relevant. Here the complete re-annotation of the genome sequence of Mycobacterium tuberculosis strain H37Rv is presented almost 4 years after the first submission. Eighty-two new protein-coding sequences (CDS) have been included and 22 of these have a predicted function. The majority were identified by manual or automated re-analysis of the genome and most of them were shorter than the 100 codon cut-off used in the initial genome analysis. The functional classification of 643 CDS has been changed based principally on recent sequence comparisons and new experimental data from the literature. More than 300 gene names and over 1000 targeted citations have been added and the lengths of 60 genes have been modified. Presently, it is possible to assign a function to 2058 proteins (52% of the 3995 proteins predicted) and only 376 putative proteins share no homology with known proteins and thus could be unique to M. tuberculosis.

Virulence and immunity are poorly understood in Mycobacterium tuberculosis. We sequenced the complete genome of the M. tuberculosis clinical strain CDC1551 and performed a whole-genome comparison with the laboratory strain H37Rv in order to identify polymorphic sequences with potential relevance to disease pathogenesis, immunity, and evolution. We found large-sequence and single-nucleotide polymorphisms in numerous genes. Polymorphic loci included a phospholipase C, a membrane lipoprotein, members of an adenylate cyclase gene family, and members of the PE/PPE gene family, some of which have been implicated in virulence or the host immune response. Several gene families, including the PE/PPE gene family, also had significantly higher synonymous and nonsynonymous substitution frequencies compared to the genome as a whole. We tested a large sample of M. tuberculosis clinical isolates for a subset of the large-sequence and single-nucleotide polymorphisms and found widespread genetic variability at many of these loci. We performed phylogenetic and epidemiological analysis to investigate the evolutionary relationships among isolates and the origins of specific polymorphic loci. A number of these polymorphisms appear to have occurred multiple times as independent events, suggesting that these changes may be under selective pressure. Together, these results demonstrate that polymorphisms among M. tuberculosis strains are more extensive than initially anticipated, and genetic variation may have an important role in disease pathogenesis and immunity.

Countless millions of people have died from tuberculosis, a chronic infectious disease caused by the tubercle bacillus. The complete genome sequence of the best-characterized strain of Mycobacterium tuberculosis, H37Rv, has been determined and analysed in order to improve our understanding of the biology of this slow-growing pathogen and to help the conception of new prophylactic and therapeutic interventions. The genome comprises 4,411,529 base pairs, contains around 4,000 genes, and has a very high guanine + cytosine content that is reflected in the biased amino-acid content of the proteins. M. tuberculosis differs radically from other bacteria in that a very large portion of its coding capacity is devoted to the production of enzymes involved in lipogenesis and lipolysis, and to two new families of glycine-rich proteins with a repetitive structure that may represent a source of antigenic variation.