Mycolic acid composition and thermally adaptative changes in Nocardia asteroides

Mycotic acid composition of Corynebacterium glutamicum and its cell surface mutants: effects of growth with glycine and isonicotinic acid hydrazide

Auxotrophic mutants of Corynebacterium glutamicum strain ATCC 13059 (parent of AS019, a rifampicin-resistant variant), which were morphologically distinct from the parent and formed protoplasts more readily, had been isolated previously. Mutants MLB130-133 and MLB194 were more sensitive to growth inhibition by isonicotinic acid hydrazide (INH) and glycine, which caused branching and budding. Fatty acid and mycolic acid (MA) profiles were determined after growth in LBG (Luria broth plus glucose), LBG-glycine (LBG- and LBG-INH (LBG-I). The fatty acid profiles of all strains were similar, except that mutant MLB133 showed some increase in stearic acid (C18:0), normally a minor component, late in the growth cycle and oleic acid proportionately decreased. All strains had five major types of MAs (C32:0, C34:0, C34:1, C36:1, C36:2) but the relative proportion of each varied with the strain, age of culture and medium composition. Mutants MLB133 and MLB194 showed slightly higher levels of non-covalentiy bound MAs than the parent and normally showed a higher proportion of longer-chained, unsaturated MAs. The proportion of extracellular MAs increased with culture age for these mutants. Typically, by late stationary phase, mycolic acids in culture fluids increased to 6.5% of the total MAs for MLB194 and 7.9% for MLB133 compared with 3.5% for the parent strain grown in LBG. The main effect of glycine (2%, w/v) addition was to increase the proportion of mycolic acids found in extracellular fluids (16.1 % for AS019 and 31% for MLB133). The most significant effects of INH were seen when strains were cultured in LBG with 8 mg INH ml−1. When harvested at late stationary phase, strains MLB133 and MLB194 had 18.8% and 21.2% extracellular mycolic acids respectively, with a significant increase in the relative proportion of unsaturated mycolic acids. This effect was not as marked for AS019, which also showed a similar decrease in C32:0 relative to increases in the proportion of C34:1 and C36:2 plus a corresponding increase in the overall proportion of unsaturated mycolic acids and increased extracellular mycolates (8.5%). These results suggest that the mutations in strains MLB133 and MLB194 are associated with synthesis of specific mycolic acids (e.g. C32:0) and attachment of mycolic acids to the cell surface, both of which are likely target sites for glycine and INH action for cell-surface modifications. In addition to previously reported targeting of the peptidoglycan cross-linking, these results show that glycine affects mycolic acid attachment to the cell surface of C. glutamicum.

Drug sensitivity and environmental adaptation of mycobacterial cell wall components

The intrinsic resistance of many mycobacterial species to chemotherapy is largely attributable to their impermeable cell wall. The composition of the cell wall of a particular species appears to be influenced by the environmental niche that the species occupies. The complex regulatory and biosynthetic pathways involved in cell wall biosynthesis and construction offer useful chemotherapeutic targets against mycobacteria.

Nocardia species: host-parasite relationships

The nocardiae are bacteria belonging to the aerobic actinomycetes. They are an important part of the normal soil microflora worldwide. The type species, Nocardia asteroides, and N. brasiliensis, N. farcinica, N. otitidiscaviarum, N. nova, and N. transvalensis cause a variety of diseases in both normal and immunocompromised humans and animals. The mechanisms of pathogenesis are complex, not fully understood, and include the capacity to evade or neutralize the myriad microbicidal activities of the host. The relative virulence of N. asteroides correlates with the ability to inhibit phagosome-lysosome fusion in phagocytes; to neutralize phagosomal acidification; to detoxify the microbicidal products of oxidative metabolism; to modify phagocyte function; to grow within phagocytic cells; and to attach to, penetrate, and grow within host cells. Both activated macrophages and immunologically specific T lymphocytes constitute the major mechanisms for host resistance to nocardial infection, whereas B lymphocytes and humoral immunity do not appear to be as important in protecting the host. Thus, the nocardiae are facultative intracellular pathogens that can persist within the host, probably in a cryptic form (L-form), for life. Silent invasion of brain cells by some Nocardia strains can induce neurodegeneration in experimental animals; however, the role of nocardiae in neurodegenerative diseases in humans needs to be investigated.

Nocardia species: host-parasite relationships

The nocardiae are bacteria belonging to the aerobic actinomycetes. They are an important part of the normal soil microflora worldwide. The type species, Nocardia asteroides, and N. brasiliensis, N. farcinica, N. otitidiscaviarum, N. nova, and N. transvalensis cause a variety of diseases in both normal and immunocompromised humans and animals. The mechanisms of pathogenesis are complex, not fully understood, and include the capacity to evade or neutralize the myriad microbicidal activities of the host. The relative virulence of N. asteroides correlates with the ability to inhibit phagosome-lysosome fusion in phagocytes; to neutralize phagosomal acidification; to detoxify the microbicidal products of oxidative metabolism; to modify phagocyte function; to grow within phagocytic cells; and to attach to, penetrate, and grow within host cells. Both activated macrophages and immunologically specific T lymphocytes constitute the major mechanisms for host resistance to nocardial infection, whereas B lymphocytes and humoral immunity do not appear to be as important in protecting the host. Thus, the nocardiae are facultative intracellular pathogens that can persist within the host, probably in a cryptic form (L-form), for life. Silent invasion of brain cells by some Nocardia strains can induce neurodegeneration in experimental animals; however, the role of nocardiae in neurodegenerative diseases in humans needs to be investigated.

High-performance liquid chromatography patterns of mycolic acids as criteria for identification of Mycobacterium chelonae, Mycobacterium fortuitum, and Mycobacterium smegmatis

Rapidly growing mycobacteria of clinical significance were identified by mycolic acids detected with high-performance liquid chromatography. Mycolic acids from whole cells were extracted, derivatized, and detected by a modified high-performance liquid chromatography procedure in less than 3 h. Use of an internal standard allowed differentiation of Mycobacterium chelonae and Mycobacterium fortuitum by comparison of relative retention times. Peak height ratios were used for subidentification of M. chelonae strains; however, M. fortuitum and Mycobacterium smegmatis could not be separated by this system.

Molecular species of mycolic acid subclasses in eight strains of Mycobacterium smegmatis

Thin layer chromatographic and gas chromatographic separation and mass spectrometric identification of mycolic acid subclasses and molecular species from eight strains of Mycobacterium smegmatis were established. Two major adjacent spots and a lower minor one were detected on silica gel thin layer chromatograms of methyl esters. The most abundant subclass showing the highest Rf value on TLC was that of alpha-mycolic acids (M1), the second was that of alpha-mycolic acids (M1), a shorter homologue than alpha-mycolates, and the third was the hydroxy mycolic acids (M4) derived from epoxy mycolic acids. They were identified by gas chromatography-mass spectrometry as their trimethylsilylether derivatives. alpha'-Mycolic acids were monoenoic acids ranging from C60 to C66 and possessing an alpha-unit of C24:0. Such profiles of alpha'-mycolic acids were common in eight strains. alpha-Mycolates were dienoic acids ranging from C75 to C79 and possessing an alpha-unit of C24:0. In most strains, the major molecular species of alpha-mycolates were odd-carbon-numbered, centering at C77 and C79, possessing a methyl branch in the even-carbon-numbered straight chain. The average carbon number of alpha-mycolates, from seven strains examined, was about 78, but that of the Takeo strain was 76.3. The profiles of epoxy mycolic acid molecular species composition from eight strains ranging from C75 to C81 were very similar to their M1 subclass profiles.

Effect of growth stage on mycolic acid structure in cell walls of Nocardia asteroides GUH-2

Mycolic acids were extracted from the cell walls of Nocardia asteroides GUH-2 during different phases of growth at 37 degrees C. These were subjected to structural analysis by combining thin-layer chromatography and gas-liquid chromatography with UV and infrared spectrophotometry and mass spectroscopy of both methyl esters and trimethyl silyl derivatives. By analyzing the fragmentation patterns of these derivatives by three different methods of mass spectroscopy combined with gas-liquid chromatographic separation, the different structural subclasses of mycolic acids were quantitated. Significant qualitative and quantitative modifications of specific mycolic acid subclasses occurred in the cell walls of N. asteroides GUH-2 that were growth stage dependent. The mycolic acids that were predominant in the log phase were polyunsaturated (greater than 2 double bonds per molecule), with long chain lengths and even carbon atom numbers (i.e., C54, C56). In contrast, those that were prominent in the stationary phase were more saturated (few or no double bonds) and of shorter overall carbon chain length (less than or equal to C52). Furthermore, stationary-phase cells had significantly increased amounts of mycolic acids with odd-numbered carbon chain lengths (i.e., C49, C51, C53).

Relationship among cell wall composition, stage of growth, and virulence of Nocardia asteroides GUH-2

The clearance and organ distribution of virulent Nocardia asteroides GUH-2P and the avirulent mutant GUH-2AI at different stages of growth was determined after intravenous inoculation into BALB/c mice. The mutant differed significantly from the parent strain in its ability to survive and grow within the murine host. Since the mutant GUH-2AI had a very different colonial morphology compared with GUH-2P, it was believed that cell surface components might be affected by the mutation that resulted in the loss of virulence. Therefore, cell walls of both GUH-2P and GUH-2AI at different stages of growth were prepared and their composition determined. There were growth-stage-dependent changes in the composition of the cell walls that appeared to correlate with concurrent alterations in virulence; however, the overall chemical composition of the cell wall of the mutant (GUH-2AI) was not significantly different from that of the parent strain (GUH-2P). Both strains demonstrated significant modifications in fatty and mycolic acid composition at different stages of growth. Furthermore, the specific composition of C54 mycolic acids was very different in virulent log-phase cells compared with less-virulent stationary-phase cells, and the avirulent mutant lacked a C54:3 mycolate that was prominent in the virulent log-phase GUH-2P. Thus, C54:3 mycolic acid represented 2.5% of the cell wall (dry weight) in log-phase GUH-2P, but it was undetectable in the walls of GUH-2AI at the stationary phase of growth. These results suggest that certain mycolic acids are associated with virulence.

Determination of molecular species composition of C80 or longer-chain alpha-mycolic acids in Mycobacterium spp. by gas chromatography-mass spectrometry and mass chromatography

The molecular species composition of alpha-mycolic acids ranging from C68 to C86 in 13 rapidly growing and 12 slowly growing mycobacterial species was determined by gas chromatography, gas chromatography-mass spectrometry, and mass chromatography. In gas chromatographic analysis, the molecular species of alpha-mycolic acids were well separated as trimethylsilyl ether derivatives of the methyl esters, according to their total carbon numbers. The total carbon and double-bond numbers of mycolic acids at each peak on gas chromatograms were determined from the [M]+, [M - 15]+, and [M - 90]+ ions on the mass spectrum, and straight and branched chain structures were identified by the mass fragment ions [A]+, due to C2--C3 cleavage [R-CH-O-Si(CH3)3]+, and [B]+, due to C3--C4 cleavage [(CH3)3-Si-O-CH-CH(R')-COOCH3]+. The concentration of odd- and even-carbon-numbered mycolic acids, which often overlap each other on gas chromatograms, and the composition of three homologous mycolic acids with different alpha units (C22:0, C24:0, and C26:0) were clearly determined by mass chromatography monitoring [M - 15]+ ions and [B - 29]+ ions, respectively. The molecular species composition of alpha-mycolic acids and their average carbon numbers (av. cn.) as a simple expression of the composition were calculated from the mass chromatograms. Each mycobacterial species examined was demonstrated to possess a characteristic profile of alpha-mycolic acid composition, and based on this the species were classified approximately into eight groups: C68 to C76 (av. cn. 72), dienoic, possessing a C20 alkyl branch at the 2 position (C22 alpha-unit) for Mycobacterium diernhoferi and Mycobacterium sp. strain 3707, a chromogenic rapid grower; C72 to C78 (av. cn. 75), dienoic with both C22 and C24 alpha units, containing a small or a large amount of odd-carbon-numbered molecules, for M. vaccae, M. rhodesiae, and M. phlei (chromogenic rapid growers); C72 to C80 (av. cn. 75 to 77), dienoic with C24 alpha-unit, containing a moderate or a large amount of odd-carbon-numbered molecules, for M. smegmatis, M. chitae, M. chelonae (M. chelonei), and M. fortuitum (nonchromogenic rapid growers); C78 to C82 (av. cn. 80), even-carbon-numbered dienoic with C24 alpha unit for M. agri and M. thermoresistible (rapid growers); C75 to C81 (av. cn. 77 to 79), odd-carbon-numbered dienoic with C24 alpha unit for M. nonchromogenicum complex (M. nonchromogenicum, M. terrae, and "M. novum") (slow growers); (vi) C76 to C84 (av. cn. 79 to 81), even-carbon-numbered dienoic with C24 alpha unit for MAIS complex including M. scrofulaceum, M. avium, and M. intracellulare (slow growers); (vii) C72 to C80 (av. cn. 77 to 79), even-carbon-numbered dienoic with C24 alpha unit for M. szulgai, M. gordonae, and M. kansasii (chromogenic slow growers); and (viii) C76 to C86 (av. cn. 79 to 81), even-carbon-numbered dienoic with C26 alpha unit M. bovis Ravenol and BCG and M. tuberculosis H37Rv. This study demonstrated that gas chromatography-mass spectrometric analysis of the molecular species composition of alpha-mycolic acid can give rapid, important, and very precise information for the identification of pathogenic and nonpathogenic mycobacterial species.

Isonicotinic acid hydrazide induced changes and inhibition in mycolic acid synthesis in Nocardia and related taxa

The mycolic acid compositions of Nocardia rubra and related bacteria grown in media containing different concentrations of antituberculous isonicotinic acid hydrazide (INH) were determined in detail by gas chromatography-mass spectrometry. On the basis of molecular species composition, average carbon numbers of mycolic acids were calculated. In Nocardia rubra, N. lutea and Rhodococcus rhodochrous IFO-13161, the ratio of mycolic to non-mycolic fatty acids and the average carbon numbers of mycolic acids were decreased at the INH concentrations of higher than 1 microgram/ml, paralleling with the significant inhibition of growth. In above three species the synthesis of longer chain mycolic acids (longer than C44 or C46 ) was inhibited more significantly than shorter homologues such as C38 or C40 . In contrast, neither growth inhibition nor change in corynomycolic acid composition was observed in Corynebacteria xerosis and Rhodococcus rhodochrous IFO-13165 at the concentration region of INH up to 100 micrograms/ml. The direct mass fragmentographic analysis of the trimethylsilylated (TMS) derivatives of mycolic acid methyl esters, monitoring [M-15] ions of individual molecular species, revealed that the chain shortening of total mycolic acid molecule by INH occurred more greatly in more highly unsaturated subclasses than in less unsaturated subclasses. Furthermore, mass fragmentographic analysis, monitoring fragment ions (A) and (B), due to straight chain and branched chain alkyl units, respectively, demonstrated the inhibition of mycolic acids was not attributed to the shortening of alpha-alkyl chain, but to the inhibition of chain elongation of C28 to C32 straight chain meromycolic acids. It was also indicated the amounts of trehalose mono- and di- mycolate (cord factor) decreased significantly with the addition of INH (1 to 20 micrograms/ml) in the above strains. From the results obtained above, INH appeared to inhibit the synthesis of mycolic acids longer than C44 or C46 specifically by inhibiting chain elongation or desaturation of precursor long chain fatty acids longer than C28 or C30.

In vitro synthesis of mycolic acids by the fluffy layer fraction of Bacterionema matruchotii

Biosynthetic activity for mycolic acid occurred in the fluffy layer fraction but not in the 5000g supernatant of Bacterionema matruchotii. With [1-14C]palmitic acid as precursor for the in vitro system, the predominant product was identified as C32:0 mycolic acid by radio-gas-liquid chromatographic (radio-GLC) and gas chromatographic/mass spectroscopic analyses; if [1-14C]stearic acid was used, two major radioactive peaks appeared on GLC: one corresponding to the peak of (C34:0 + C34:1) mycolic acids and the other to (C36:0 + C36:1) mycolic acids. By pyrolysis/radio-GLC analysis, C32:0 mycolic acid synthesized by [1-14C]palmitic acid was pyrolyzed at 300 degrees C to form palmitaldehyde (the mero moiety) and methyl palmitate (the branch moiety). The pH optimum for the incorporation of [1-14C]palmitate into bacterionema mycolic acids was 6.4 and the reaction required a divalent cation. The in vitro system utilized myristic, palmitic, stearic and oleic acids (probably via their activated forms) well as precursors, among which myristic and palmitic acids were more effective than the rest. Avidin showed no effect on the biosynthesis of mycolic acid from 14C-palmitate whereas cerulenin, a specific inhibitor of beta-ketoacyl synthetase in de novo fatty acid synthesis, inhibited the reaction at a relatively higher concentration. Thin-layer chromatographic analysis of lipids extracted from the reacting mixture without alkaline hydrolysis showed that both exogenous [1-14C]fatty acid and synthesized mycolic acids were bound to an unknown compound by an alkali-labile linkage and this association seemed to occur prior to the condensation of two molecules of fatty acid.

Separation and analysis of novel polyunsaturated mycolic acids from a psychrophilic, acid-fast bacterium, Gordona aurantiaca

More than 30 molecular species of highly unsaturated mycolic acids, ranging from C60 to C78 and possessing between two and seven double bonds, have been obtained from a new genus of acid-fast bacteria, Gordona aurantiaca. They were fully separated and identified as their trimethylsilyl ether derivatives by a combination of silica gel thin-layer chromatography (TLC), argentation thin-layer chromatography and gas chromatography/mass spectrometry (GC/MS). On silica gel thin-layer chromatography two adjacent spots, corresponding to mycolic acids possessing different structures of straight-chain and alpha-alkyl branch, were detected. The lower spot was separated by argentation TLC into four subclasses: monoenoic (including a small amount of saturated), dienoic, trienoic and tetraenoic mycolic acids ranging from C62 to C74 and possessing a C16:0, C18:0 or C20:0 alkyl branch at the C-2 position. The upper spot was separated by argentation TLC into five subclasses: dienoic (including a small amount of monoenoic), trienoic, tetraenoic, pentaenoic and hexaenoic (heptaenoic) acids ranging from C64 to C78 and possessing a C18:1 or C20:1 alkyl branch at the C-2 position. These types of mycolic acid structure differ from those reported previously in Mycobacteria and Nocardia, in the numbers of both carbon atoms and double-bonds and the intermediate length of the alpha-alkyl branch. The characteristic polyenoic structure of the straight-chain alkyl unit was also confirmed by GC/MS analysis of the meromycolaldehydes obtained after pyrolysis of the methyl mycolates. The major aldehydes obtained from the lower-spot mycolic acids were C44, C46, C48, C50 and C52, while those from the upper-spot mycolic acids were C48, C50, C52, C54 and C56, centering at C54. These aldehydes were also shown to possess between two and four double bonds in the lower-spot and between two and seven double bonds in the higher-spot mycolic acids, respectively. The physiological role of such highly polyunsaturated mycolic acids in psychrophilic acid-fast bacteria is discussed.