Inactivation of polyketide synthase and related genes results in the loss of complex lipids in Mycobacterium tuberculosis H37Rv.

AIMS: Phthiocerol dimycocerosate (PDIM) waxes and other lipids are necessary for successful Mycobacterium tuberculosis infection, although the exact role of PDIM in host-pathogen interactions remains unclear. In this study, we investigated the contribution of tesA, drrB, pks6 and pks11 genes in complex lipid biosynthesis in M. tuberculosis. METHODS AND RESULTS: Four mutants were selected from M. tuberculosis H37Rv transposon mutant library. The transposon insertion sites were confirmed to be within the M. tuberculosis open reading frames for tesA (a probable thioesterase), drrB (predicted ABC transporter), pks11 (putative chalcone synthase) and pks6 (polyketide synthase). The first three of these transposon mutants were unable to generate PDIM and the fourth lacked novel polar lipids. CONCLUSIONS: Mycobacterium tuberculosis can be cultivated in vitro without the involvement of certain lipid synthesis genes, which may be necessary for in vivo pathogenicity. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of transposon mutants is a new functional genomic approach for the eventual definition of the mycobacterial 'lipidome'.

Mycolic acids and ancient DNA confirm an osteological diagnosis of tuberculosis.

SETTING: The underlying trends in the past epidemiology of tuberculosis (TB) are obscure, requiring recourse to the archaeological record. It would therefore be of value to develop methods for reliable TB diagnosis in ancient populations. OBJECTIVE: To test the capability of two biomarkers, Mycobacterium tuberculosis complex mycolic acids and a DNA target (IS6110), for confirming an osteological diagnosis of TB in medieval individuals, based on the presence of Pott's disease and/or rib lesions. DESIGN: Osteological examination of three archaeological individuals (Medieval: approximately 1000 years old) revealed a Pott's disease case, one with no changes consistent with TB and one with rib lesions. Rib samples from these individuals were examined for the presence of Mycobacterium tuberculosis complex mycolic acids and mycobacterial DNA. RESULTS: Mycobacterium tuberculosis complex mycolic acids and the DNA target were detected in the Pott's disease case, whilst mycolic acids (insufficient for confirmation) alone were detected in the rib lesion case. CONCLUSIONS: Biomarkers provide a sensitive tool to detect ancient TB. Mycobacterium tuberculosis DNA is not distributed homogeneously, making multiple sampling essential. Mycolic acids seem more reliable for ancient TB diagnosis than IS6110. The demonstrated stability of mycolic acids show that they may be of value in tracing the palaeoepidemiology of tuberculosis back into antiquity.

Biochemical characterization of acyl carrier protein (AcpM) and malonyl-CoA:AcpM transacylase (mtFabD), two major components of Mycobacterium tuberculosis fatty acid synthase II.

Malonyl coenzyme A (CoA)-acyl carrier protein (ACP) transacylase (MCAT) is an essential enzyme in the biosynthesis of fatty acids in all bacteria, including Mycobacterium tuberculosis. MCAT catalyzes the transacylation of malonate from malonyl-CoA to activated holo-ACP, to generate malonyl-ACP, which is an elongation substrate in fatty acid biosynthesis. To clarify the roles of the mycobacterial acyl carrier protein (AcpM) and MCAT in fatty acid and mycolic acid biosynthesis, we have cloned, expressed, and purified acpM and mtfabD (malonyl-CoA:AcpM transacylase) from M. tuberculosis. According to the culture conditions used, AcpM was produced in Escherichia coli in two or three different forms: apo-AcpM, holo-AcpM, and palmitoylated-AcpM, as revealed by electrospray mass spectrometry. The mtfabD gene encoding a putative MCAT was used to complement a thermosensitive E. coli fabD mutant. Expression and purification of mtFabD resulted in an active enzyme displaying strong MCAT activity in vitro. Enzymatic studies using different ACP substrates established that holo-AcpM constitutes the preferred substrate for mtFabD. In order to provide further insight into the structure-function relationship of mtFabD, different mutant proteins were generated. All mutations (Q9A, R116A, H194A, Q243A, S91T, and S91A) completely abrogated MCAT activity in vitro, thus underlining the importance of these residues in transacylation. The generation and characterization of the AcpM forms and mtFabD opens the way for further studies relating to fatty acid and mycolic acid biosynthesis to be explored in M. tuberculosis. Since a specific type of FabD is found in mycobacterial species, it represents an attractive new drug target waiting to be exploited.

Amycolatopsis sacchari sp. nov., a moderately thermophilic actinomycete isolated from vegetable matter.

The taxonomic position of a group of moderately thermophilic actinomycetes isolated from vegetable matter was determined using a suite of genotypic and phenotypic properties. The organisms were found to share a range of chemical and morphological markers typical of members of the genus Amycolatopsis. A representative of the group, strain K24T, formed a distinct phyletic line within the range of variation occupied by the genus Amycolatopsis in the 16S rDNA tree. The strains have many phenotypic properties in common and some of these distinguish the group from representatives of the validly described species of Amycolatopsis. It is clear from the combined datasets that the strains merit recognition as a new species of Amycolatopsis. The name proposed for the new species is Amycolatopsis sacchari; the type strain is K24T (= DSM 44468T = KCTC 9863T).

Thiolactomycin and related analogues as novel anti-mycobacterial agents targeting KasA and KasB condensing enzymes in Mycobacterium tuberculosis.

Prevention efforts and control of tuberculosis are seriously hampered by the appearance of multidrug-resistant strains of Mycobacterium tuberculosis, dictating new approaches to the treatment of the disease. Thiolactomycin (TLM) is a unique thiolactone that has been shown to exhibit anti-mycobacterial activity by specifically inhibiting fatty acid and mycolic acid biosynthesis. In this study, we present evidence that TLM targets two beta-ketoacyl-acyl-carrier protein synthases, KasA and KasB, consistent with the fact that both enzymes belong to the fatty-acid synthase type II system involved in fatty acid and mycolic acid biosynthesis. Overexpression of KasA, KasB, and KasAB in Mycobacterium bovis BCG increased in vivo and in vitro resistance against TLM. In addition, a multidrug-resistant clinical isolate was also found to be highly sensitive to TLM, indicating promise in counteracting multidrug-resistant strains of M. tuberculosis. The design and synthesis of several TLM derivatives have led to compounds more potent both in vitro against fatty acid and mycolic acid biosynthesis and in vivo against M. tuberculosis. Finally, a three-dimensional structural model of KasA has also been generated to improve understanding of the catalytic site of mycobacterial Kas proteins and to provide a more rational approach to the design of new drugs.

Activation of human neutrophils by mycobacterial phenolic glycolipids.

The interaction between mycobacterial phenolic glycolipids (PGLs) and phagocytes was studied. Human neutrophils were allowed to interact with each of four purified mycobacterial PGLs and the neutrophil production of reactive oxygen metabolites was followed kinetically by luminol-/isoluminol-amplified chemiluminescence. The PGLs from Mycobacterium tuberculosis and Mycobacterium kansasii, respectively, were shown to stimulate the production of oxygen metabolites, while PGLs from Mycobacterium marinum and Mycobacterium bovis BCG, respectively, were unable to induce an oxidative response. Periodate treatment of the M. tuberculosis PGL decreased the production of oxygen radicals, showing the importance of the PGL carbohydrate moiety for the interaction. The activation, however, could not be inhibited by rhamnose or fucose, indicating a complex interaction which probably involves more than one saccharide unit. This is in line with the fact that the activating PGLs from M. tuberculosis and M. kansasii contain tri- and tetrasaccharides, respectively, while the nonactivating PGLs from M. marinum and M. bovis BCG each contain a monosaccharide. The complement receptor 3 (CR3) has earlier been shown to be of importance for the phagocyte binding of mycobacteria, but did not appear to be involved in the activation of neutrophils by PGLs. The subcellular localization of the reactive oxygen metabolites formed was related to the way in which the glycolipids were presented to the cells.

Antimycobacterial activities of isoxyl and new derivatives through the inhibition of mycolic acid synthesis.

Isoxyl (ISO), a thiourea (thiocarlide; 4, 4'-diisoamyloxythiocarbanilide), demonstrated potent activity against Mycobacterium tuberculosis H37Rv (MIC, 2.5 micrograms/ml), Mycobacterium bovis BCG (MIC, 0.5 microgram/ml), Mycobacterium avium (MIC, 2.0 microgram/ml), and Mycobacterium aurum A+ (MIC, 2.0 microgram/ml), resulting in complete inhibition of mycobacteria grown on solid media. Importantly, a panel of clinical isolates of M. tuberculosis from different geographical areas with various drug resistance patterns were all sensitive to ISO in the range of 1 to 10 microgram/ml. In a murine macrophage model, ISO exhibited bactericidal killing of viable intracellular M. tuberculosis in a dose-dependent manner (0.05 to 2.50 microgram/ml). The selective action of ISO on mycolic acid synthesis was studied through the use of [1, 2-14C]acetate labeling of M. tuberculosis H37Rv, M. bovis BCG, and M. aurum A+. At its MIC for M. tuberculosis, ISO inhibited the synthesis of both fatty acids and mycolic acids (alpha-mycolates by 91.6%, methoxymycolates by 94.3%, and ketomycolates by 91.1%); at its MIC in M. bovis BCG, ISO inhibited the synthesis of alpha-mycolates by 87.2% and that of ketomycolates by 88.5%; and the corresponding inhibitions for M. aurum A+ were 87.1% for alpha-mycolates, 87.2% for ketomycolates, and 86.5% for the wax-ester mycolates. A comparison with isoniazid (INH) and ethionamide (ETH) demonstrated marked similarity in action, i.e., inhibition of the synthesis of all kinds of mycolic acids. However, unlike INH and ETH, ISO also inhibited the synthesis of shorter-chain fatty acids. ISO showed no acute toxicity against primary macrophage cell cultures as demonstrated by diminution of redox activity. A homologous series of ISO derivatives were synthesized. Most derivatives were as effective or more effective than the parent compound in the agar proportion assay. Thus, these thioureas, like INH and ETH, specifically inhibit mycolic acid synthesis and show promise in counteracting a wide variety of drug-sensitive and -resistant strains of M. tuberculosis.

Lipid domains of mycobacteria studied with fluorescent molecular probes.

The complex mycobacterial cell envelope is recognized as a critical factor in our failure to control tuberculosis, leprosy and other non-tuberculous pathogens. Although its composition has been extensively determined, many details regarding the organization of the envelope remain uncertain. This is particularly so for the non-covalently bound lipids, whose natural distribution may be disrupted by conventional biochemical or cytological techniques. In order to study the native organization of lipid domains in the mycobacterial envelope, we have applied a range of fluorescent lipophilic probes to live mycobacteria, including Mycobacterium smegmatis, Mycobacterium tuberculosis, Mycobacterium avium, Mycobacterium gadium and Mycobacterium aurum, and analysed the resultant signals by fluorescence microscopy and digital image processing. Five key features were observed: (i) the presence of both envelope and intracellular lipid domains; (ii) differential localization of probes into these domains influenced predominantly by their hydrophobicity, as modelled by their calculated octanol:water partition coefficients and by their amphiphilicities; (iii) uneven distribution of lipophilic material in the envelope; (iv) selective labelling of septal regions of the envelope; and (v) modification of labelling patterns by additional treatments such as fluorescence quenching antibodies, detergents and solvents. Using this last approach, a coherent cell envelope lipid domain was demonstrated outside the cytoplasmic membrane and, for the first time, the proposed covalently linked mycolyl-arabinogalactan-peptidoglycan macromolecular complex was imaged directly. The use of fluorescent probes and high-resolution fluorescence microscopy has enabled us to obtain a coherent view of distinct lipid domains in mycobacteria. Further application of this approach will facilitate understanding of the role of lipids in the physiology of these organisms.

Structure of a new glycolipid from the Mycobacterium avium-Mycobacterium intracellulare complex.

From the lipid fraction of a freeze-dried cell mass of a strain of the Mycobacterium avium-Mycobacterium intracellulare complex, a new glycolipid was isolated and was characterized as 5-mycoloyl-alpha-arabinofuranosyl (1-->1')-glycerol, mainly on the basis of nuclear magnetic resonance spectroscopy studies.

Classification of thermophilic streptomycetes, including the description of Streptomyces thermoalcalitolerans sp. nov.

A polyphasic taxonomic study was undertaken to clarify relationships within and between representative thermophilic alkalitolerant streptomycetes isolated from soil and appropriate marker strains. The resultant data, notably those from DNA-DNA relatedness studies, support the taxonomic integrity of the validly described species Streptomyces thermodiastaticus, Streptomyces thermoviolaceus and Streptomyces thermovulgaris. However, the genotypic and phenotypic data clearly show that Streptomyces thermonitrificans Desai and Dhala 1967 and S. thermovulgaris (Henssen 1957) Goodfellow et al. 1987 represent a single species. On the basis of priority, S. thermonitrificans is a later subjective synonym of S. thermovulgaris. Similarly, 10 out of the 11 representative thermophilic alkalitolerant isolates had a combination of properties consistent with their classification as S. thermovulgaris. The remaining thermophilic alkalitolerant isolate, Streptomyces strain TA56, merited species status. The name Streptomyces thermoalcalitolerans sp. nov. is proposed for this strain. A neutrophilic thermophilic isolate, Streptomyces strain NAR85, was identified as S. thermodiastaticus.

Mycobacterium tuberculosis complex DNA in calcified pleura from remains 1400 years old.

Mycobacterium tuberculosis complex DNA was isolated and identified in calcified pleura from remains 1400 years old, with the polymerase chain reaction. This is the first demonstration of tuberculosis in non-mummified archaeological tissue other than bone; the presence of mycobacterial mycolic acids in the sample supports this conclusion. The study of ancient DNA from microbial pathogens is of interest as it enables verification of traditional diagnoses, may answer long-standing questions in the history of disease, and provides ancient DNA sequences that can be compared with those of modern isolates.

Serotaxonomic analysis of glycolipids from Mycobacterium chelonae-M. fortuitum complex and bovine farcy strains.

The antigenicity and cross-reactivity of glycolipids from strains of bovine farcy and the Mycobacterium chelonae-M. fortuitum complex were analyzed using the ELISA technique. Purified alkali-stable glycopeptidolipids (GPLs) with a characteristic dimethylrhamnosyl sugar unit extracted from M. abscessus, M. chelonae, M. peregrinum and M. senegalense, gave very strong reactions with sera against members of the same four species. Particularly strong cross-reactions were evident between M. peregrinum and M. senegalense. These GPLs reacted more weakly with antisera against the other mycobacteria tested, though clear reactions were noticed with M. farcinogenes and M. fortuitum and also with M. bovis BCG, M. phlei, and M. tuberculosis strains. Alkali-labile diacyl trehalose (DAT) and triacyl trehalose (TAT) from M. fortuitum reacted with homologous sera, and with that against M. tuberculosis. Traces of uncharacterized acyl trehaloses isolated from two strains of M. farcinogenes gave comparatively weak reactions. Mycobacteria labeled M. farcinogenes and M. senegalense produced glucosylated trehalose-based glycolipids (GTs) and the studies showed that the major type was antigenic. These glycolipids cross-reacted strongly with M. senegalense NCTC 4524 but not with the type strain of M. senegalense. On the basis of the chemical patterns and the antigenicity of the GPLs it is evident that M. peregrinum and M. senegalense are particularly closely related and these species show a very close affinity to M. abscessus-M. chelonae.

Structures of phenolic glycolipids from Mycobacterium kansasii.

From the lipid fraction of cells of Mycobacterium kansasii, four phenolic glycolipids K5, K6, K7 and K8, were isolated, in addition to three known phenolic glycolipids KI, KII and KIV. K5 was identified as a tetraglycosyl phenolic glycolipid whose sugar moiety was 2,6-dideoxy-4-O-methyl-L-alpha-arabinohexopyranosyl(1-->3)-4-O-pro pionyl-2-O-methyl-L-alpha-fucopyranosyl(1-->3)-2-O-methyl-L-alpha-rhamno pyranosyl-(1-->3)-2,4-di-O-methyl-L-alpha-rhamnopyranosyl(1-->) and phenolic glycolipid K6 as deacetyl-KI. Glycolipids K7 and K8 were triglycosyl phenolic glycolipids having the sugar moieties of 2-O-methyl-L-alpha-fucopyranosyl(1-->3)-2-O-methyl-L-alpha-rhamnopyranos yl(1-->3)-2,4-di-O-methy-L-alpha-rhamnopyranosyl(1-->) and 2-O-methyl-L-alpha-fucopyranosyl(1-->3)-2-O-methyl-L-alpha-rhamnopyranos yl(1-->3)-2-O-methyl-L-alpha-rhamnopyranosyl(1-->), respectively. Phenolic glycolipids K6 and K7 have been referred to as controlled degradation products of phenolic glycolipid KI previously. Also isolated was 5-mycolyl-beta-arabinofuranosyl(1-->2)-5-mycolyl-alpha-ar abinofurnosyl(1-->1')-glycerol, an analogue of glycolipid ai, originally isolated from Mycobacterium avium-Mycobacterium intracellulare complex, having mycolic acids of M. kansasii.

A chemotaxonomic study of the lipoglycans of Rhodococcus rhodnii N445 (NCIMB 11279).

Rhodococcus rhodnii N445 was investigated for the presence of macroamphiphilic lipoglycan. Purification of a hot phenol-water extract by hydrophobic interaction chromatography allowed the resolution of three lipoglycan fractions. The two main preparations contained lipoglycans with carbohydrate compositions consistent with the presence of lipoarabinomannan and lipomannan, whilst the minor fraction appeared to contain a mixture of these two lipoglycans. The fatty acid composition of the lipoglycans resembled that of the whole cells except that the relative proportion of unsaturated fatty acids was decreased. Although lipoarabinomannan and structurally-related lipomannan lipoglycans from representatives of the genus Mycobacterium have been extensively studied, this is the first report of the lipoglycan composition of a representative of the genus Rhodococcus as presently defined. These findings provide further chemotaxonomic evidence that lipoarabinomannan-type lipoglycans are widely distributed throughout the mycolic acid-containing actinomycetes.

Synthesis of racemic 2,4-dimethyltetradecanoic acid from Mycobacterium kansasii.

A known intermediate, (3 R, S; 5 R,S)-3,5-dimethyl-6-triphenylmethyloxyhexanal gave, in a Wittig reaction with 1-octyltriphenylphosphonium bromide and n-butyl lithium in anhydrous tetrahydrofuran, a mixture of olefininic compounds. Trityl deprotection and hydrogenation of the double bond afforded the (2 R, S; 4 R,S)-2,4-dimethyltetradecanols. Oxidation of the alcohol functionality using pyridinium dichromate in anhydrous N,N'-dimethylformamide gave racemic, (2 R, S; 4 R,S)-2,4-dimethyltetradecanoic acids, which were converted to their methyl esters. 2,4-Dimethyltetradecanoic acids are constituents of glycolipid antigens from Mycobacterium kansasii.

Distribution of antibody titres against phenolic glycolipids from Mycobacterium tuberculosis in the sera from tuberculosis patients and healthy controls.

Sera from tuberculosis (TB) patients and healthy controls were tested by ELISA for their antibody titres against the two major phenolic glycolipids (PGLs) of Mycobacterium tuberculosis, PGL-tbO (a 1:3 mixture of PGL-tb1 and its analogue whose phthiocerol moiety is phenolphthiotriol A) and PGL-tbK. Both PGL-tbs were shown to be specific to M. tuberculosis, and the profiles of serum anti-PGL-tbK titres revealed that PGL-tbK, like PGL-tb1, was fairly widely distributed among strains of M. tuberculosis. Even when these two PGL-tbs were used, however, the rate of ELISA-positives was not very high among TB patients, which is probably explained by the nature of the disease. Moreover, a considerable number of sera from healthy controls, especially from younger age groups, had high anti-PGL-tb titres, which implies that environmental exposure to M. tuberculosis is much higher than has been estimated from the actual TB cases. The ELISA system using these species-specific PGL-tb antigens may be useful for the survey of TB infection, since it gives more direct information on TB infection than the PPD skin test.

A new group (type 3) of Mycobacterium celatum isolated from AIDS patients in the London area.

We describe a new group (type 3) of the recently proposed species Mycobacterium celatum isolated from eight patients with AIDS in London, England. Sequences of genes coding for 16S rRNA (EMBL accession no. Z46664) showed a divergence of 17 bases from M. celatum type 2 reference isolates and a divergence of 7 bases from M. celatum type 1 reference isolates. A reference strain is available (NCTC 12882).

Stereochemistry of 2,4-dimethyleicos-2-enoate from the pyruvylated glycolipid of Mycobacterium smegmatis.

The absolute stereochemistry of 2,4-dimethyleicos-2-enoic acid, isolated from the pyruvylated glycolipid of Mycobacterium smegmatis, has been determined. The two enantiomers of methyl 2,4-dimethyleicos-2-enoate were synthesised for the first time but could not be separated by gas chromatography on cyclodextrin phases. (E)-2-Methyloctadec-2-enoate, an intermediate in the synthesis, is a characteristic component of acyl trehalose glycolipids from Mycobacterium fortuitum. Ozonolysis of the fatty acid ester mixture, obtained from the pyruvylated glycolipid produced 2-methyloctadecanoate. It was identified as the (S)-enantiomer by comparison with (2R) and (2S)-2-methyloctadecanoic acid, intermediates in the synthesis of (4R)- and (4S)-2,4,-dimethyleicos-2-enoic acid, using enantioselective gas chromatography of the methyl esters with heptakis(2,6-di-O-methyl-3-O-pentyl)-beta-cyclodextrin as a chiral stationary phase. The natural acid was therefore determined to be 2E-(4S)-2,4-dimethyleicos-2-enoic acid.

Thin-layer chromatography and mass spectrometry of pentafluorobenzylidene derivatives of members of the phthiocerol family from Mycobacterium tuberculosis and Mycobacterium marinum.

The difference in relative stereochemistry of the 1.3-diol unit of mycobacterial phthiocerols can be determined by simple thin-layer chromatographic analysis of pentafluorobenzylidene acetal derivatives. The threo phthiocerol acetals from Mycobacterium tuberculosis are composed of equal amounts of two axial-equatorial stereoisomers but the erythro phthiocerols from Mycobacterium marinum form only one acetal with diequatorial substituents. The two acetals formed from a threo phthiocerol can be separated by thin-layer chromatography and mass spectra of the two stereoisomers allowed assignment of their structures.

Characterization of the specific antigenicity of representatives of M. senegalense and related bacteria.

Representative strains of M. senegalense and an unusual strain, labelled M. farcinogenes (M280) were examined by thin-layer chromatography for the presence of characteristic surface glycolipids. In the case of M. farcinogenes M280 and M. senegalense M264, the glycolipids were of the alkali-labile acyltrehalose lipooligosaccharide (LOS) class of antigens, whereas M. senegalense M263 was found to contain the alkali-stable glycopeptidolipids (GPL). Through a combination of 1H-NMR, methylation analysis, FAB/MS, and other analytical techniques, the structures of these glycolipids were deduced. The LOS glycolipids were found to be similar in structure to the characteristic glucosyltrehalose-based glycolipids isolated previously from clinical isolates of M. fortuitum, but distinct from the diacyltrehaloses characteristic of the type strain of M fortuitum. The glycopeptidolipids from M. senegalense M263 were closely similar to those characterized previously from M.