Primary structure of the wall peptidoglycan of leprosy-derived corynebacteria

Identification and Characterization of a Cell Wall Hydrolase for Sporangiospore Maturation in Actinoplanes missouriensis

The rare actinomycete Actinoplanes missouriensis grows as substrate mycelium and forms terminal sporangia containing a few hundred spores as dormant cells. Upon contact with water, the sporangia open up and release spores to external environments. Here, we report a cell wall hydrolase, GsmA, that is required for sporangiospore maturation in A. missouriensis The gsmA gene is conserved among Actinoplanes species and several species of other rare actinomycetes. Transcription of gsmA is activated in the late stage of sporangium formation by the global transcriptional activator TcrA, which is involved in sporangium formation and dehiscence. GsmA is composed of an N-terminal signal peptide for the twin arginine translocation pathway, two tandem bacterial SH3-like domains, and a glucosaminidase domain. Zymographic analysis using a recombinant C-terminal glucosaminidase domain protein showed that GsmA is a hydrolase able to digest cell walls extracted from the vegetative mycelia of A. missouriensis and Streptomyces griseus A gsmA deletion mutant (ΔgsmA) formed apparently normal sporangia, but they released chains of 2 to 20 spores under sporangium dehiscence-inducing conditions, indicating that spores did not completely mature in the mutant sporangia. From these results, we concluded that GsmA is a cell wall hydrolase for digesting peptidoglycan at septum-forming sites to separate adjacent spores during sporangiospore maturation in A. missouriensis Unexpectedly, flagella were observed around the spore chains of the ΔgsmA mutant by transmission electron microscopy. The flagellar formation was strictly restricted to cell-cell interfaces, giving an important insight into the polarity of the flagellar biogenesis in a spherical spore.IMPORTANCE In streptomycetes, an aerial hypha is compartmentalized by multiple septations into prespores, which become spores through a series of maturation processes. However, little is known about these maturation processes. The rare actinomycete Actinoplanes missouriensis produces sporangiospores, which are assumed to be formed also from prespores generated by the compartmentalization of intrasporangium hyphae via septation. The identification of GsmA as a cell wall hydrolase for the separation of adjacent spores sheds light on the almost unknown processes of sporangiospore formation in A. missouriensis Furthermore, the fact that GsmA orthologues are conserved within the genus Actinoplanes but not in streptomycetes indicates that Actinoplanes has developed an original strategy for the spore maturation in a specific environment, that is, inside a sporangium.

Use of a codon alteration strategy in a novel approach to cloning the Mycobacterium tuberculosis diaminopimelic acid epimerase

Previous attempts to express the diaminopimelate epimerase gene dapF of Mycobacterium tuberculosis in Escherichia coli resulted in undetectable enzyme yields. We used silent mutation of the first 10 codons of the recombinant ORF in an attempt to reduce the formation of secondary structures that might occur near the 5' end of the mRNA and inhibit translation. This significantly increased the yield of the enzyme, which was purified and characterized biochemically. This strategy could be generally applied to other mycobacterial genes that are difficult to express hetero-specifically and here provided pure M. tuberculosis DapF, a good foundation for future research in antimycobacterial agents.

Comparative cell wall core biosynthesis in the mycolated pathogens, Mycobacterium tuberculosis and Corynebacterium diphtheriae

The recent determination of the complete genome sequence of Corynebacterium diphtheriae, the aetiological agent of diphtheria, has allowed a detailed comparison of its physiology with that of its closest sequenced pathogenic relative Mycobacterium tuberculosis. Of major importance to the pathogenicity and resilience of the latter is its particularly complex cell envelope. The corynebacteria share many of the features of this extraordinary structure although to a lesser level of complexity. The cell envelope of M. tuberculosis has provided the molecular targets for several of the major anti-tubercular drugs. Given a backdrop of emerging multi-drug resistant strains of the organism (MDR-TB) and its continuing global threat to human health, the search for novel anti-tubercular agents is of paramount importance. The unique structure of this cell wall and the importance of its integrity to the viability of the organism suggest that the search for novel drug targets within the array of enzymes responsible for its construction may prove fruitful. Although the application of modern bioinformatics techniques to the 'mining' of the M. tuberculosis genome has already increased our knowledge of the biosynthesis and assembly of the mycobacterial cell wall, several issues remain uncertain. Further analysis by comparison with its relatives may bring clarity and aid the early identification of novel cellular targets for new anti-tuberculosis drugs. In order to facilitate this aim, this review intends to illustrate the broad similarities and highlight the structural differences between the two bacterial envelopes and discuss the genetics of their biosynthesis.

Biochemistry and comparative genomics of SxxK superfamily acyltransferases offer a clue to the mycobacterial paradox: presence of penicillin-susceptible target proteins versus lack of efficiency of penicillin as therapeutic agent

The bacterial acyltransferases of the SxxK superfamily vary enormously in sequence and function, with conservation of particular amino acid groups and all-alpha and alpha/beta folds. They occur as independent entities (free-standing polypeptides) and as modules linked to other polypeptides (protein fusions). They can be classified into three groups. The group I SxxK D,D-acyltransferases are ubiquitous in the bacterial world. They invariably bear the motifs SxxK, SxN(D), and KT(S)G. Anchored in the plasma membrane with the bulk of the polypeptide chain exposed on the outer face of it, they are implicated in the synthesis of wall peptidoglycans of the most frequently encountered (4-->3) type. They are inactivated by penicillin and other beta-lactam antibiotics acting as suicide carbonyl donors in the form of penicillin-binding proteins (PBPs). They are components of a morphogenetic apparatus which, as a whole, controls multiple parameters such as shape and size and allows the bacterial cells to enlarge and duplicate their particular pattern. Class A PBP fusions comprise a glycosyltransferase module fused to an SxxK acyltransferase of class A. Class B PBP fusions comprise a linker, i.e., protein recognition, module fused to an SxxK acyltransferase of class B. They ensure the remodeling of the (4-->3) peptidoglycans in a cell cycle-dependent manner. The free-standing PBPs hydrolyze D,D peptide bonds. The group II SxxK acyltransferases frequently have a partially modified bar code, but the SxxK motif is invariant. They react with penicillin in various ways and illustrate the great plasticity of the catalytic centers. The secreted free-standing PBPs, the serine beta-lactamases, and the penicillin sensors of several penicillin sensory transducers help the D,D-acyltransferases of group I escape penicillin action. The group III SxxK acyltransferases are indistinguishable from the PBP fusion proteins of group I in motifs and membrane topology, but they resist penicillin. They are referred to as Pen(r) protein fusions. Plausible hypotheses are put forward on the roles that the Pen(r) protein fusions, acting as L,D-acyltransferases, may play in the (3-->3) peptidoglycan-synthesizing molecular machines. Shifting the wall peptidoglycan from the (4-->3) type to the (3-->3) type could help Mycobacterium tuberculosis and Mycobacterium leprae survive by making them penicillin resistant.

DNA methylation in leprosy-associated bacteria: Mycobacterium leprae and Corynebacterium tuberculostearicum

The DNAs of two kinds of microorganisms from human leprosy lesion, Mycobacterium leprae and Corynebacterium tuberculostearicum (also known as "leprosy-derived corynebacterium" or LDC), have been analysed and compared with the genomes of reference bacteria of the CMN group (genera Corynebacterium, Mycobacterium and Nocardia). The guanine-plus-cytosine content (% GC) of DNA was determined by a double-labelling procedure, which is unaffected by the presence of modified and unusual bases (that alter both buoyant density and mid-melting-point determinations). Accordingly, the DNAs of seven LDC strains had GC values of 54-56 mol %, and that of armadillo-grown M. leprae a value of 54.8 +/- 0.9 mol %. Restriction patterns disclosed no methylated cytosine in the DNA sequences CCGG, GGCC, AGCT and GATC of either LDC or M. leprae DNA. N6-methyl adenine was present in the sequence GATC of all LDC strains, but was missing from the genomes of all others CMN organisms analysed, including M. leprae. By HPLC analysis of LDC-DNA hydrolysates, it was found that N6-methyladenine amounted to 1.8% of total DNA adenine, and was present exclusively within GATC sequences, which appeared all to be methylated. It is concluded that LDC represent a group of corynebacteria endowed with high genetic homogeneity and a unique restriction pattern, whereby their genome is easily distinguished from that of M. leprae, which has a similar base composition.

Biological, chemical, immunological and staining properties of bacteria isolated from tissues of leprosy patients

Two kinds of microorganisms are found in tissue of leprosy patients: Mycobacterium leprae (ML) and leprosy derived corynebacteria (LDC). ML from untreated patients has an alcohol-acid-fastness, which is lost upon treatment with antibiotics and immune response (tuberculoid leprosy). Vulnerable ML thus produced can be reversibly de-stained by organic solvent: in tissue sections from tuberculoid and treated patients, more bacteria are, thus, revealed by the Wade-Fite than by the Ziehl-Neelsen procedure. Organisms of genera Corynebacterium, Mycobacterium and Nocardia (CMN group), have DNA with %GC contents of 50-70, 69-72, and 68-70 respectively. GC values of DNA from ML and LDC are close to 56%. DNA from different LDC strains display high homology among them and low homology with reference corynebacteria. CMN cell wall consists of interconnected peptidoglycan and polysaccharide-mycolate complex. Peptidoglycan of LDC (and known CMN) has the polysaccharide backbone linked to a tetrapeptide of L-Ala, D-Glu, m-DAP (meso-diaminopimelate), D-Ala. In ML, L-Ala is replaced by glycine. Mycobacterial wall polysaccharides (that of ML is unknown) are branched arabinogalactans with end arabinoses linked to C70 to C90 mycolates. LDC peripheral polysaccharides are arabinogalactomannans with arabinose and mannose lateral strands. Mycolic acids of LDC are of corynomycolic type (C32, C34 and C36 with 1-4 double bonds) and those of ML are of mycobacterial type. Components of CMN wall and cytoplasm are immunologically active as antigens (polysaccharides, proteins), haptens (lipids) and adjuvants (peptidoglycans). Strong intrageneric and weak intergenera crossreactions are observed among CMN bacteria: LDC preparations, however, crossreact strongly with ML and mycobacteria, and weakly with reference corynebacteria. LDC in leprosy tissues can, thus, be revealed as well by fluorescent anti-LDC antisera as by anti-ML antisera. The main crossreacting component is antigen M1 of LDC, which corresponds to antigens Ag 7 of ML and Ag60 of BCG, the active components of lepromin and tuberculin (known reagents for cutaneous tests). Antigen M1 has a polysaccharide moiety crossreacting with the wall polysaccharide of LDC.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of the cytoplasmic antigens of leprosy-derived corynebacteria and some mycobacteria

The immunological relationship between leprosy-derived corynebacteria (LDC) and reference mycobacteria was analysed by crossed immunoelectrophoresis with intermediate gel. For this purpose, three reference systems (LDC15/anti-LDC15, LDC18/anti-LDC8, and LDC8/anti-LDC8) were developed. They showed 15 to 20 distinct antigenic components in LDC cytoplasm. Extensive cross-reactivity was observed among different LDC isolates, affecting 3 to 17 components. Moreover, several components were shown to cross-react with mycobacteria when anti-bacillus Calmette-Guérin (BCG), anti-Mycobacterium leprae, other antisera and lepromatous leprosy sera were incorporated in the intermediate gel. The major cross-reactive component, antigen M, was present in all LDC isolates and cross-reacted with antigen 7 of M. leprae and antigen 60 of M. bovis BCG. The thermostability of these antigens and the specificity of the cross-reacting antigens were assessed. The data underline the degree of immunochemical homogeneity within the LDC group of micro-organisms and relatedness with M. leprae and other mycobacteria.

Analysis of mycolic acids from a group of corynebacteria by capillary gas chromatography and mass spectrometry

The cell wall of leprosy-derived corynebacteria (a group of 'diphtheroids' isolated from human leprosy lesions and patients' blood) was previously shown to contain, in addition to peptidoglycan and arabinogalactan, mycolic acids. These alpha-branched beta-hydroxy fatty acids were attributed to the corynomycolic group, according to their RF in monodimensional thin-layer chromatography. In the present work, mycolic acids from leprosy-derived and reference corynebacteria have been fractionated by monodimensional and bidimensional thin-layer chromatography and by gas chromatography. Pyrolyzed mycolic acids have been analyzed on conventional packed columns, whereas intact methyl esters of mycolic acids with free and silylated beta-hydroxyl group have been analyzed on capillary columns, and their structure has been established by mass spectrometry. In all leprosy-derived corynebacteria, some 20 components containing 24-36 carbon atoms and 0-4 double bonds were obtained. The three major groups had 32, 34 and 36 carbons, and the frequency of unsaturated versus saturated chains increased proportionally to the molecular weight. For comparison, the main components of a reference corynebacterium. Corynebacterium diphtheriae PW8, had 30 and 32 carbons, and their hydrocarbon chains were essentially saturated. This work confirms the relative chemical homogeneity of different leprosy-derived corynebacteria and describes some peculiar traits in the chemical structure of this group of organisms. In addition, it shows the complexity of the mycolic acid fraction of corynebacterial cell wall and suggests that the mycolic acid pattern is a sort of fingerprint of each bacterial strain grown under standard conditions. Finally, the fractionation of intact corynomycolic acid methyl esters with free or silylated beta-hydroxyl group by capillary gas chromatography proved to be the best analytical procedure at present available for resolving this complex mixture of corynomycolate isomers. Structural determination of silylated samples by mass spectrometry is preferred because they have more diagnostic fragments.