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PubMed2005

Biosynthesis and identification of volatiles released by the myxobacterium Stigmatella aurantiaca.

The volatiles released by agar plate cultures of two strains of the myxobacterium Stigmatella aurantiaca (strains Sg a15 and DW4/3-1) were collected in a closed-loop stripping apparatus (CLSA) and analyzed by GC-MS. Large numbers of substances from different compound classes (ketones, esters, lactones, terpenes, and sulfur and nitrogen compounds) were identified; several of them are reported from natural sources for the first time. The volatiles 2-methyltridecan-4-one (17), its isomer 3-methyltridecan-4-one (20), and the higher homologue 2-methyltetradecan-4-one (18) were identified in the extracts of both strains and were synthesized. In addition, strain Sg a15 produced 2,12-dimethyltridecan-4-one (19), 2-methyltridec-2-en-4-one (23), and a series of phenyl ketones, among them 1-phenyldecan-1-one (14) and 9-methyl-1-phenyldecan-1-one (16), whereas strain DW4/3-1 emitted traces of 10-methylundecan-2-one (21). The biosynthesis of 14 and 16 was examined in feeding experiments with deuterated precursors carried out on agar plate cultures. The leucine-derived starter unit isovalerate was shown to be incorporated into 16, as was phenylalanine-derived benzoic acid into both 14 and 16. The results point to formation both of the phenyl ketones and of the structurally related aliphatic ketones through an unusual head-to-head coupling between a starter unit such as benzoyl-CoA and a fatty acyl-CoA, followed by decarboxylation.

Benzoic Acid↗
PubMed2005

The pyruvate kinase of Stigmatella aurantiaca is an indole binding protein and essential for development.

Myxospore formation of the myxobacterium Stigmatella aurantiaca can be uncoupled from the cooperative development i.e. fruiting body formation, by low concentrations of indole. Two putative indole receptor proteins were isolated by their capacity to bind indole and identified as pyruvate kinase (PK) and aldehyde dehydrogenase. The PK activity of Stigmatella crude extracts was stimulated by indole. Cloning of the PK gene (pykA) and the construction of a pykA disruption mutant strikingly revealed that PK is essential for multicellular development: Fruiting body formation was abolished in the mutant strain and indole-induced spore formation was delayed. The developmental defects could be complemented by insertion of the pykA gene at the mtaB locus of the Stigmatella genome excluding any polar effects of the pykA disruption.

Bacterial Proteins↗
PubMed1993

Selective amplification of DNA fragments coding for the G domain of factors IF2 and EF-Tu, two G proteins from the myxobacterium Stigmatella aurantiaca.

Two DNA fragments of the genome of the myxobacterium Stigmatella aurantiaca were selectively amplified by PCR. These fragments encode a segment of the G domain of translational initiation factor IF2 and elongation factor EF-Tu, two GTP-binding proteins. This was made possible by carefully designing the primers for this reaction to avoid the amplification of every G-domain-encoding region of the genome. The sequence of two pairs of primers was deduced from highly conserved regions, namely G1 and G3 and/or their vicinal amino acids, within each subfamily (initiation and elongation factors, respectively) of GTP-binding proteins. On the basis of the expected size, one band was selected in each experiment, cloned into a vector, and sequenced. This showed unambiguously after comparison analysis that they belong to the IF2 and EF-Tu genes, respectively. This strategy seems suitable for the amplification of a segment of any gene coding for a G protein from any origin.

Amino Acid Sequence↗
PubMed1982

Pheromone produced by the myxobacterium Stigmatella aurantiaca.

An extracellular, diffusible signaling molecule (pheromone) was produced by Stigmatella aurantiaca during fruiting body formation. The pheromone decreased the aggregation period in both the light and the dark and substituted for light in stimulating the maturation of aggregates into fruiting bodies. The cells were more sensitive to lower concentrations of pheromone in the light than in the dark, possibly explaining the stimulation of aggregation and fruiting body formation by light. The pheromone also interacted cooperatively with GMP to shorten the aggregation period. The pheromone behaved chemically as a low-molecular-weight lipid.

Animals↗
PubMed2001

SigB, an alternative sigma factor of the myxobacterium Stigmatella aurantiaca, is synthesized during development and heat shock.

Alternative sigma factors have been detected in the myxobacterium Stigmatella aurantiaca during indole-induced sporulation, fruiting body formation and heat shock using an antiserum raised against sigma factor SigB. The time course of sigB gene expression was analysed by RT-PCR and by determining beta-galactosidase activity during development in a merodiploid strain that harboured a sigB-lacZ fusion gene. Inactivation of the sigB gene by insertion of the neo gene resulted in the loss of one sigma factor as shown by Western analysis. Neither fruiting body formation nor sporulation, nor the production of possible SigB targets, such as DnaK, GroEL or HspA, were affected.

Bacterial Proteins↗
PubMed2000

The myxochelin iron transport regulon of the myxobacterium Stigmatella aurantiaca Sg a15.

The biosynthetic gene cluster of the myxochelin-type iron chelator was cloned from Stigmatella aurantiaca Sg a15 and characterized. This catecholate siderophore was only known from two other myxobacteria. The biosynthetic genes of 2,3-dihydroxybenzoic acid are located in the cluster (mxcC-mxcF). Two molecules of 2, 3-dihydroxybenzoic acid are activated and condensed with lysine in a unique way by a protein homologous to nonribosomal peptide synthetases (MxcG). Inactivation of mxcG, which encodes an adenylation domain for lysine, results in a myxochelin negative mutant unable to grow under iron-limiting conditions. Growth could be restored by adding Fe3+, myxochelin A or B to the medium. Inactivation of mxcD leads to the same phenotype. A new type of reductive release from nonribosomal peptide synthetases of the 2, 3-dihydroxybenzoic acid bis-amide of lysine from MxcG, catalyzed by a protein domain with homology to NAD(P) binding sites, is discussed. The product of a gene, encoding a protein similar to glutamate-1-semialdehyde 2,1-aminomutases (mxcL), is assumed to transaminate the aldehyde that is proposed as an intermediate. Further genes encoding proteins homologous to typical iron utilization and iron uptake polypeptides are reported.

Amino Acid Sequence↗
PubMed2001

The mtaA gene of the myxothiazol biosynthetic gene cluster from Stigmatella aurantiaca DW4/3-1 encodes a phosphopantetheinyl transferase that activates polyketide synthases and polypeptide synthetases.

Myxothiazol is synthesized by the myxobacterium Stigmatella aurantiaca DW4/3-1 via a combined polyketide synthase/polypeptide synthetase. The biosynthesis of this secondary metabolite is also dependent on the gene product of mtaA. The deduced amino acid sequence of mtaA shows similarity to 4'-phosphopantetheinyl transferases (4'-PP transferase). This points to an enzyme activity that converts inactive forms of the acyl carrier protein domains of polyketide synthetases (PKSs) and/or the peptidyl carrier protein domains of nonribosomal polypeptide synthetases (NRPSs) of the myxothiazol synthetase complex to their corresponding holo-forms. Heterologous co-expression of MtaA with an acyl carrier protein domain of the myxothiazol synthetase was performed in Escherichia coli. The proposed function as a 4'-PP transferase was confirmed and emphasizes the significance of MtaA for the formation of a catalytically active myxothiazol synthetase complex. Additionally, it is shown that MtaA has a relaxed substrate specificity: it processes an aryl carrier protein domain derived from the enterobactin synthetase of E. coli (ArCP) as well as a peptidyl carrier protein domain from a polypeptide synthetase of yet unknown function from Sorangium cellulosum. Therefore, MtaA should be a useful tool for activating heterologously expressed PKS and NRPS systems.

Adenosine Triphosphatases↗
PubMed1997

Bifunctional structure of two adenylyl cyclases from the myxobacterium Stigmatella aurantiaca.

Two adenylyl cyclase genes (cyaA and cyaB) from the myxobacterium Stigmatella aurantiaca were cloned by complementation of Escherichia coli mutants defective in the cya gene. cyaA codes for a protein of 424 amino acid residues (AC1), while cyaB encodes a protein of 352 residues (AC2). Both cyclases are sensitive to adenosine: cAMP production was strongly inhibited in E coli cells and cell extracts expressing these genes. AC1 comprises a hydrophobic domain of six transmembrane helices coupled to a cytoplasmic catalytic domain endowed with adenylyl cyclase activity. A 17 amino acid residue sequence, which is a signature of G-protein coupled receptors, as well as of slime mold Dictyostelium discoideum cyclic AMP receptors, was found in the membrane domain. AC2 displays features also indicating that it is a bifunctional enzyme. The domain located upstream from the catalytic adenylyl cyclase domain shows strong similarity to receiver modules of response regulators of two-component bacterial signaling systems. In vitro mutagenesis of conserved aspartate residues in this domain was shown to interfere with cAMP synthesis.

Adenosine↗
PubMed1998

Intercellular signaling in Stigmatella aurantiaca: purification and characterization of stigmolone, a myxobacterial pheromone.

The myxobacterium Stigmatella aurantiaca passes through a life cycle that involves formation of a multicellular fruiting body as the most complex stage. An early step in this differentiation process depends on a signal factor secreted by the cells when nutrients become limited. The formation of a fruiting body from a small cell population can be accelerated by addition of this secreted material. The bioactive compound was found to be steam volatile. It was purified to homogeneity by steam distillation followed by reversed-phase and normal-phase HPLC. The pheromone was named stigmolone, in accordance with the structure 2,5, 8-trimethyl-8-hydroxy-nonan-4-one, as determined by NMR and mass spectrometry. Stigmolone represents a structurally unique and highly bioactive prokaryotic pheromone that is effective in the bioassay at 1 nM concentration.

Alkanes↗
PubMed1980

Effects of specific cations on aggregation and fruiting body morphology in the myxobacterium Stigmatella aurantiaca.

The cation requirements for fruiting body formation in the myxobacterium Stigmatella aurantiaca on agarose were determined. Calcium alone caused the cells to aggregate into interconnecting ridges. Under these conditions, stalk formation was severely depressed but sporangia frequently formed. The combination of magnesium and manganese was necessary for optimal formation of discrete aggregates (rather than ridges) and stalks. Manganese inhibited sporangium development. The inclusion of calcium into the magnesium-manganese medium overcame the inhibition by manganese and stimulated the production of multiple sporangia.

Calcium↗
PubMed1983

Occurrence of dialkyl ether phospholipids in Stigmatella aurantiaca DW4.

We investigated the lipid composition of vegetative cells of Stigmatella aurantiaca. Four phospholipids were isolated and identified: phosphatidylethanolamine as the main component, phosphatidylglycerol, lysophosphatidylethanolamine in an exceptionally large amount (17%), and phosphatidylinositol (18 to 25%), rare in procaryotic cells. This composition did not change significantly during growth. The fatty acids of total lipids were found to be rather similar to those of other strains of myxobacteria; the main fatty acids found were unsaturated and branched. We noted a different fatty acid pattern for each phospholipid. The presence of unusual alkyl ether linkages, established by chemical hydrolysis and infrared spectroscopy, was unexpected in these bacteria. Diacyl ester, dialkyl ether, and monoacyl-monoalkyl structures were shown in phosphatidylethanolamine and phosphatidylglycerol. Lysophosphatidylethanolamine was essentially a monoacyl form, whereas phosphatidylinositol was a unique dialkyl ether phospholipid.

Fatty Acids↗
PubMed2005

Structure and biosynthesis of myxochromides S1-3 in Stigmatella aurantiaca: evidence for an iterative bacterial type I polyketide synthase and for module skipping in nonribosomal peptide biosynthesis.

The myxobacterium Stigmatella aurantiaca DW4/3-1 harbours an astonishing variety of secondary metabolic gene clusters, at least two of which were found by gene inactivation experiments to be connected to the biosynthesis of previously unknown metabolites. In this study, we elucidate the structures of myxochromides S1-3, novel cyclic pentapeptide natural products possessing unsaturated polyketide side chains, and identify the corresponding biosynthetic gene locus, made up of six nonribosomal peptide synthetase modules. By analyzing the deduced substrate specificities of the adenylation domains, it is shown that module 4 is most probably skipped during the biosynthetic process. The polyketide synthase MchA harbours only one module and is presumably responsible for the formation of the variable complete polyketide side chains. These data indicate that MchA is responsible for an unusual iterative polyketide chain assembly.

Amino Acid Sequence↗
PubMed1994

Cloning and characterization of the gene encoding the major sigma factor of Stigmatella aurantiaca.

The gene (sigA) encoding the major sigma factor of the myxobacterium, Stigmatella aurantiaca, was cloned and sequenced. The deduced polypeptide contains 706 amino acids (aa) and has a deduced M(r) of 79,910. It exhibits four different aa sequence motifs which correlate with the conserved domains of the major sigma factors of Myxococcus xanthus (sigma 80), Escherichia coli (sigma 70) and Bacillus subtilis (sigma 43). The sigma factor (sigma A) was detected in crude lysates of vegetative cells and in cells of different developmental stages from S. aurantiaca with an antiserum to M. xanthus sigma 80 by Western blot analysis. The SigA polypeptide copurified with RNA polymerase from vegetative S. aurantiaca cells. The aa sequence of its N terminus matches a sequence located 25 codons downstream from the proposed start codon. The sigA gene was expressed in E. coli and the corresponding gene product cross-reacted with the SigA antiserum as a polypeptide of 100 kDa, which is identical in size to the sigma A detected in vegetative cells of S. aurantiaca.

Amino Acid Sequence↗
PubMed1992

Purification of the DNA-dependent RNA polymerase from the myxobacterium Stigmatella aurantiaca.

The DNA-dependent RNA polymerase (EC 2.7.7.6) of the myxobacterium Stigmatella aurantiaca has been purified. It shows three main polypeptide bands with apparent molecular weights of 146,000, 105,000, and 40,000 in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. beta and beta' subunits of the S. aurantiaca polymerase were shown to migrate in the 146,000-molecular-weight polypeptide band and the main sigma factor was shown to migrate in the 105,000-molecular-weight band by using heterologous antisera.

DNA-Directed RNA Polymerases↗
PubMed1995

Genetic and molecular analysis of the tRNA-tufB operon of the myxobacterium Stigmatella aurantiaca.

The tufB gene, encoding elongation factor Tu (EF-Tu), from the myxobacterium Stigmatella aurantiaca was cloned and sequenced. It is preceded by four tRNA genes, the first ever described in myxobacteria. The tRNA synthesized from these genes and the general organization of the locus seem identical to that of Escherichia coli, but differences of potential importance were found in the tRNA sequences and in the intergenic regions. The primary structure of EF-Tu was deduced from the tufB DNA sequence. The factor is composed of 396 amino acids, with a predicted molecular mass of 43.4 kDa, which was confirmed by expression of tufB in maxicells. Sequence comparisons between S.aurantiaca EF-Tu and other bacterial homologues from E.coli, Salmonella typhimurium and Thermus thermophilus displayed extensive homologies (75.9%). Among the variable positions, two Cys residues probably involved in the temperature sensitivity of E.coli and S.typhimurium EF-Tu are replaced in T.thermophilus and S.aurantiaca EF-Tu. Since two or even three tuf genes have been described in other bacterial species, the presence of multiple tuf genes was sought for. Southern and Northern analysis are consistent with two tuf genes in the genome of S.aurantiaca. Primer extension experiments indicate that the four tRNA genes and tufB are organized in a single operon.

Base Sequence↗
PubMed1985

Morphogenesis of Stigmatella aurantiaca fruiting bodies.

Scanning electron micrographs of intermediate stages of fruiting body formation in the myxobacterium Stigmatella aurantiaca suggest that fruiting body formation can be divided into several stages distinguishable on the basis of the motile behavior of the cells. Aggregates formed at sites where cells glide as groups in circles or spirals. Thus, each aggregate was surrounded by a wide band of cells. Several streams of cells were pointed toward and connected to the wide band of cells at the base of the aggregate, suggesting directed cell movement toward the aggregate. The pattern of cells at the base of taller, more mature aggregates suggested that groups of cells enter the aggregate from the surrounding band of cells by changing the pitch of their movement, thus creating an ascending spiral. Stalk formation was characterized by a distinctly different pattern, which suggested that single cells emerge from the band of cells and move toward the aggregate, under it, and then vertically to create the stalk. At this stage, the aggregate appeared to be torn from the substrate as it was lifted off the surface. The cells in the completed stalks were well separated, and most had their long axes pointed in a vertical direction. A great deal of the stalk material appeared to be slime in which the cells were embedded and through which they were presumably moving in the live material. Some suggestions regarding factors that may direct the observed morphogenetic movements are discussed.

Cell Division↗
PubMed1999

New lessons for combinatorial biosynthesis from myxobacteria. The myxothiazol biosynthetic gene cluster of Stigmatella aurantiaca DW4/3-1.

The biosynthetic mta gene cluster responsible for myxothiazol formation from the fruiting body forming myxobacterium Stigmatella aurantiaca DW4/3-1 was sequenced and analyzed. Myxothiazol, an inhibitor of the electron transport via the bc(1)-complex of the respiratory chain, is biosynthesized by a unique combination of several polyketide synthases (PKS) and nonribosomal peptide synthetases (NRPS), which are activated by the 4'-phosphopantetheinyl transferase MtaA. Genomic replacement of a fragment of mtaB and insertion of a kanamycin resistance gene into mtaA both impaired myxothiazol synthesis. Genes mtaC and mtaD encode the enzymes for bis-thiazol(ine) formation and chain extension on one pure NRPS (MtaC) and on a unique combination of PKS and NRPS (MtaD). The genes mtaE and mtaF encode PKSs including peptide fragments with homology to methyltransferases. These methyltransferase modules are assumed to be necessary for the formation of the proposed methoxy- and beta-methoxy-acrylate intermediates of myxothiazol biosynthesis. The last gene of the cluster, mtaG, again resembles a NRPS and provides insight into the mechanism of the formation of the terminal amide of myxothiazol. The carbon backbone of an amino acid added to the myxothiazol-acid is assumed to be removed via an unprecedented module with homology to monooxygenases within MtaG.

Amino Acid Sequence↗
PubMed1996

Stigmatella aurantiaca fruiting body formation is dependent on the fbfA gene encoding a polypeptide homologous to chitin synthases.

Stigmatella aurantiaca is a prokaryotic organism that undergoes a multicellular cycle of development resulting in the formation of a fruiting body. For analyzing this process, mutants defective in fruiting body formation have been induced by transposon mutagenesis using a Tn5-derived transposon. About 800 bp upstream of the transposon insertion of mutant AP182 which inactivates a gene (fbfB) involved in fruiting, a further gene (fbfA) needed for fruiting body formation was detected. Inactivation of fbfA leads to mutants which form only non-structured clumps instead of the wild-type fruiting body. The mutant phenotype of fbfA mutants can be partially suppressed by mixing the mutant cells with cells of some independent mutants defective in fruiting body formation. The fbfA gene is transcribed after 8 h of development as determined by measuring the induction of beta-galactosidase activity of a fbfA-delta(trp)-lacZ fusion gene and by Northern (RNA) analysis using an insertion encoding a stable mRNA. The predicted polypeptide FbfA shows a homology of about 30% to NodC of rhizobia, an N-acetylglucosamine-transferase which is involved in the synthesis of the sugar backbone of lipo-oligosaccharides. These induce the formation of the root nodules in the Papilionaceae. Besides the predicted molecular mass of 45.5 kDa, the hydropathy profile reveals a structural relationship to the NodC polypeptide.

Amino Acid Sequence↗