II. Produkte der Reaktion von 1-Nitroso-3-nitro-1-methyl-guanidin mit Nucleobasen, Nucleosiden, Nucleosidphosphaten und Homopolyribonucleinsäuren

1-Nitroso-3-nitro-1-methyl-guanidine (NNMG) (at pH 5,5 resp. 6,0) methylates and deaminates the bases of nucleic acids. We treated nucleic bases, nucleosides, nucleoside phosphates and homopolyribonucleic acids with NNMG and we found the following methyl derivates of adenine: 1-methyladenine, 3-methyladenine and N6-methyladenine : of guanine: 7-methylguanine and of cytosine: 1-methylcytosine and 3-methylcytosine. Moreover bases of the nucleic acids were deaminated : adenine to hypoxanthine and guanine to xanthine.

Zum Wirkungsmechanismus von 1-Nitroso-3-nitro-1-methylguanidin (NNMG) bei der Mutationsauslösung / The Mode of Action of 1-Nitroso-3-nitro-1-methyl-guanidine (NNMG) in Mutagenesis

1. The stability of NNMG with respect to pH was investigated. A maximum, with a half-life of 40 hours, was found in phosphate-citric acid buffer at pH 5. The stability decreases quickly with increasing concentration of hydroxyl ions. At the optimal mutation rate (pH 6, 37°, and shaking) the half-live is only 14,4 hours.

2. NNMG uptake (using labelled NNMG) and mutation rate in the range pH 3,5 — 8,0 show an optimum at pH 6,0/6,5 for both Escherichia coli B and the red ad- mutant E 188 of Saccharomyces cerevisiae. The pH-dependence of NNMG uptake and mutation rate is similar.

3. The methylation of nucleic acids by means of [3H]-methyl-NNMG or [14C] -methyl-NNMG in phosphate-citric acid at 37° while shaking increases with the growing concentration of hydroxyl ions. At the optimal mutation rate, however, NNMG methylates relatively poor.

4. Incorporation of radioactive NNMG into Escherichia coli B results in labelling of nucleic acids and proteins. The labelling of DNA shows an optimum at pH 6. The extent of methylation was found to be higher in vivo than in vitro.

5. In the presence of cysteine or β-mercaptoethanol nucleic acids are methylated more intensively than in the cysteine-free control experiment. After one hour the methylation was about twentyfold higher in the presence of cysteine or β-mercaptoethanol compared to the cysteine-free control experiment. The methylation in presence of SH-compounds shows a maximum at pH 6. The explanation of both a higher methylation rate and its optimum at pH 6 suggests the activation of methylation by means of sulphhydryl-groups.

Zum Wirkungsmechanismus von 1-Nitroso-3-nitro-1-methyl-guanidin bei der Mutationsauslösung

The effect of NNMG on the template activities of different polynucleotides (polyuridylic acid, polycytidylic acid, polyadenylic acid and copolymer of adenylic and guanylic acid 5,5:1) and t-RNS was studied. The maximum inhibition of the messenger activity was found for poly-C, followed by poly-Α and poly-U. The acceptor activity of t-RNA was found to be inhibited by NNMG: maximum for proline, followed by serine, leucine, phenylalanine and lysine. The mechanism of these inhibitions was studied using NNMG radioactively labelled on the methyl group. Different amounts of radioactivity were found in the various polynucleotides and t-RNS.

Analysis of the proliferative responses to peptides in individuals with vigorous Gag protein-specific proliferation

Proliferative responses to recombinant HIV proteins in infected individuals may represent a correlate of protection from disease progression. In this study, the proliferative responses to HIV p24, p55 and gp120 were evaluated in infected subjects. Whereas, vigorous proliferative responses directed at the Gag proteins were detected in several individuals, Env-specific proliferation was observed in only one subject. Epitope mapping using overlapping peptides demonstrated proliferative responses of PBMC to Gag peptides. Responses were broadly directed at multiple peptides in some subjects. Although several of the peptides that induced proliferative responses also contain CTL epitopes potentially relevant in the particular individuals, many additional Gag T cell epitopes were present in each subject. This finding may be relevant for the design and testing of HIV candidate vaccines.

Isolation from Cussonia barteri of 1'-O-chlorogenoylchlorogenic acid and 1'-O-chlorogenoylneochlorogenic acid, a new type of quinic acid esters

1'-O-Chlorogenoylchlorogenic acid and 1'-O-chlorogenoylneochlorogenic acid, a new type of quinic acid esters, have been isolated, in addition to six known quinic acid esters, rutin, and a mixture of saponins, from the methanol extract of Cussonia barteri Seemann (Araliaceae) leaves collected in Cameroon. Structure determination was achieved by NMR, mass, IR, and UV spectroscopy. All compounds were tested for inhibitory activity on 5-lipoxygenase and cyclooxygenase-1, for antimicrobial activity against Bacillus subtilis, Pseudomonas fluorescens, and Cladosporium cucumerinum, and for haemolytic activity.

Polyphasic characterization of poly-3-hydroxybutyrate-co-3-hydroxyvalerate (p(HB-co-HV)) metabolizing and denitrifying Acidovorax sp. strains

For the purpose of denitrification in small drinking water plants, a bacterial mixed population was isolated from a packed bed column bioreactor with poly-3-hydroxybutyrate-co-3-hydroxyvalerate (P(HB-co-HV)) as a substrate for the denitrification of ground water (10 degrees C). Isolates 2nIII from the mixed culture, with the ability to denitrify and metabolize P(HB-co-HV), were used as starter cultures for the elimination of nitrate in ground water. The strains were characterized by diverse techniques. Classical phenotypic studies lead to rRNA group III of the genus Pseudomonas. Results obtained by molecular techniques demonstrated that the 2nIII strains are members of the Comamonadaceae and shows similarities to the genus Acidovorax. However, an integration of the 2nIII isolates within one of the known Acidovorax species is not possible for the moment. The 2nIII starter cultures clustered close to Av. temperans according to their whole cell proteins and fatty acids, whereas in DNA/DNA hybridization no significant DNA binding (< 25%) was found. In contrast a significant but low degree of DNA/DNA hybridization was found between the 2nIII strains and Av. facilis and Av. delafieldii. Our polyphasic results lead to the conclusion that the 2nIII strains may constitute a separate Acicdovorax species.

Simocyclinones, novel cytostatic angucyclinone antibiotics produced by Streptomyces antibioticus Tü 6040. I. Taxonomy, fermentation, isolation and biological activities

Two novel angucyclinone-type antibiotics, simocyclinones D4 and D8, were detected in the mycelium extract of Streptomyces antibioticus Tü 6040 by HPLC-diode-array and HPLC-electrospray-mass-spectrometry screening. The compounds show antibiotic activities against Gram-positive bacteria and cytostatic effects on various tumor cell lines.

A putative enolpyruvyl transferase gene involved in nikkomycin biosynthesis

The nikO gene encoding a putative enolpyruvyl transferase has been identified within the Streptomyces tendae Tü901/8c nikkomycin gene cluster. nikO encodes a deduced protein of 471 amino acid residues which exhibits significant sequence similarity to UDP-N-acetylglucosamine enolpyruvyl transferase and 5-enol-pyruvylshikimate 3-phosphate synthase from various origin. The nikO gene was inactivated by inserting a kanamycin resistance cassette; the mutant did not produce biologically active nikkomycins I, J, X, and Z nor the nucleoside moieties, nikkomycins C(x) and C(z), but accumulated the novel component RT 2.0. RT 2.0 has been isolated from culture filtrate and its structure was determined by using mass spectrometry and NMR analyses as ribofuranosyl-4-formyl-4-imidazolone which represents a novel nucleoside. The putative activity of the nikO gene product in nikkomycin biosynthesis will be discussed.

Two-step fast protein liquid chromatographic purification of the Serratia marcescens hemolysin and peptide mapping with mass spectrometry

The pore forming toxin of Serratia marcescens (ShlA) is secreted and activated by an outer membrane protein (ShlB). Activation of inactive ShlA (termed ShlA*) by ShlB is dependent on phosphatidylethanolamine (PE). Activation may be a covalent modification of ShlA. To test this hypothesis, the responsible activation domain (in the N-terminal 255 amino acids of ShlA) was isolated from whole bacteria with 8 M urea in an inactive form (ShlA-255*) and from the culture supernatant in an active form (ShlA-255), followed by a two-step purification by anion-exchange chromatography and gel permeation chromatography. Comparison of a tryptic peptide map of both forms with subsequent electrospray mass spectrometry (ES-MS) and sequencing by tandem ES-MS revealed no modification. These data imply that ShlB presumably imposes a conformation on ShlA-255 that triggers activity.

Degradation of desferrioxamines by Azospirillum irakense: assignment of metabolites by HPLC/electrospray mass spectrometry

Based on a recent finding that an Azospirillum isolate ASP-1 possessing high 16S rDNA similarity to Azospirillum irakense was able to degrade desferrioxamine type siderophores (Winkelmann et al. BioMetals 9, 78-83, 1996), various members of the genus Azospirillum were analyzed for their ability to degrade desferrioxamines. While the desferrioxamine-degrading activity was absent or scarcely detectable in strains of A. lipoferum, A. brasilense, A. amazonense, degradation activity seemed to be confined to the species A. irakense (KBC-1, KA3). Also the identity of strain ASP-1 as A. irakense could be confirmed by species-specific oligonucleotide hybridization, Inter-LINE PCR fingerprinting and carbon source utilization pattern (BIOLOG) analysis. Products of desferrioxamine B degradation were analyzed by analytical HPLC and HPLC/electrospray mass spectrometry. Using whole cells and purified enzyme it was shown that the trihydroxamate desferrioxamine B (561 amu) is split at the N-terminal amide bond yielding a monohydroxamate (MH1, 219 amu) and a dihydroxamate (DH1, 361 amu) metabolite. A second monohydroxamate (MH2, 319 amu) resulted from DH1 after splitting the acetylhydroxamate bond. Minor amounts of a further dihydroxamate (DH2, 419 amu) originated from splitting the second amide bond in desferrioxamine B. In addition to desferrioxamine B, several other linear and cyclic desferrioxamines and derivatives were degraded, whereas desferricoprogen and desferri-ferrichrome were not degraded, indicating high substrate specificity of the desferrioxamine hydrolase in A. irakense species. A simple microtiter plate assay was developed which can be used to phenotypically discriminate and identify species of A. irakense from other Azospirillum species by their characteristic feature of desferrioxamine degradation.

Identification and analysis of the balhimycin biosynthetic gene cluster and its use for manipulating glycopeptide biosynthesis in Amycolatopsis mediterranei DSM5908

Seven complete genes and one incomplete gene for the biosynthesis of the glycopeptide antibiotic balhimycin were isolated from the producer, Amycolatopsis mediterranei DSM5908, by a reverse-cloning approach and characterized. Using oligonucleotides derived from glycosyltransferase sequences, a 900-bp glycosyltransferase gene fragment was amplified and used to identify a DNA fragment of 9,882 bp. Of the identified open reading frames, three (oxyA to -C) showed significant sequence similarities to cytochrome P450 monooxygenases and one (bhaA) showed similarities to halogenase, and the genes bgtfA to -C showed similarities to glycosyltransferases. Glycopeptide biosynthetic mutants were created by gene inactivation experiments eliminating oxygenase and glycosyltransferase functions. Inactivation of the oxygenase gene(s) resulted in a balhimycin mutant (SP1-1) which was not able to synthesize an antibiotically active compound. Structural analysis by high-performance liquid chromatography-mass spectrometry, fragmentation studies, and amino acid analysis demonstrated that these oxygenases are involved in the coupling of the aromatic side chains of the unusual heptapeptide. Mutant strain HD1, created by inactivation of the glycosyltransferase gene bgtfB, produced at least four different compounds which were not glycosylated but still antibiotically active.

Low level chemiluminescence from liquid culture media

Low level chemiluminescence (CL) can be observed from autoclaved liquid culture media, as used in microbiology. The light emission is oxygen-dependent and arises from reactions following auto-oxidation of reducing Maillard products which are formed during autoclaving. The inhibition of this CL by radical scavengers and antioxidants has been studied. As superoxide radicals and hydrogen peroxide are predominantly involved in the initiation of the CL, the investigation of CL from culture media offers a convenient tool for the detection of exogenous (medium-mediated) oxidative stress being imposed onto micro-organisms in culture. Transition metal ions showed, dependent on concentration, both inhibitory and stimulating effects on the CL, which was also affected by the presence of complexing agents. Iron porphyrins and related complexes displayed a very efficient quenching of the CL, which may be of particular importance, as aerobic micro-organisms have been previously shown to be very efficient in quenching the CL from culture media.

Inhibition of virulence factor expression in Staphylococcus aureus by the Staphylococcus epidermidis agr pheromone and derivatives

The agr quorum-sensing system in Staphylococci controls the production of surface proteins and exoproteins. In the pathogenic species Staphylococcus aureus, these proteins include many virulence factors. The extracellular signal of the quorum-sensing system is a thiolactone-containing peptide pheromone, whose sequence varies among the different staphylococcal strains. We demonstrate that a synthetic Staphylococcus epidermidis pheromone is a competent inhibitor of the Staphylococcus aureus agr system. Derivatives of the pheromone, in which the N-terminus or the cyclic bond structure was changed, were synthesized and their biological activity was determined. The presence of a correct N-terminus and a thiolactone were absolute prerequisites for an agr-activating effect in S. epidermidis, whereas inhibition of the S. aureus agr system was less dependent on the original structure. Our results show that effective quorum-sensing blockers that suppress the expression of virulence factors in S. aureus can be designed based on the S. epidermidis pheromone.

A model for the generation of low level chemiluminescence from microbiological growth media and its depletion by bacterial cells

We present a model for the development of chemiluminescence (CL) in autoclaved liquid growth media, as they are used in microbiology for the culturing of microorganisms, or in other related Maillard systems. The model distinguishes between four different stages consisting of sugar fragmentation during heating, autooxidation of highly reducing fragmentation products, radical chain reactions leading to a peroxidation of the media, and finally the formation of excited states, energy transfer reactions and CL emission. The proposed model is also discussed in regard of a recently reported elimination of this CL in growing cultures of microorganisms and possible pathways for this interference are suggested.

Identification of unusual amino acids in peptides using automated sequential Edman degradation coupled to direct detection by electrospray-ionization mass spectrometry

The determination of the primary structure of peptides and proteins is routine in many laboratories; however, many of the obtained sequences are incomplete or can be misinterpreted when the samples contain unusual amino acids. Here we report the development of an automated peptide sequenator coupled to an electrospray-ionization (ESI) mass spectrometer (MS) that, in conjunction with minor modifications to the sequencing conditions and, in some cases, prior derivatization of amino acids, allows the detection of the phenylthiohydantoin (PTH) derivatives of a number of unusual amino acids. Using the coupled sequenator-ESI-MS system we were able to determine the complete sequence of the lantibiotic gallidermin, a partial sequence of the calcium-dependent peptide antibiotic CDA2 as well as the pool sequence of a mixture of synthetic peptides containing nonproteinogenic amino acids. In addition to the 20 proteinogenic amino acids, the procedure was able to detect PTH derivatives of hydroxyphenylglycine, 2,3-didehydroasparagine, 3-methylglutamic acid, oxytryptophan, ornithine, N-methylglycine, dihydroxyphenylalanine, and alpha-aminoisobutyric acid. Similarly, after a simple derivatization procedure, we were also able to correctly identify educts of 2,3-didehydroalanine, 2,3-didehydrobutyrine, lanthionine, and 3-methyllanthionine.

Weak light emission patterns from lactic acid bacteria

Distinct low level chemiluminescence patterns during aerobic growth of a selection of bacterial strains of the lactic acid group were recorded in on-line measurements. These patterns may be specific for the strain and the medium employed for cultivation. The patterns are oxygen-dependent and consist in the case of Enterococcus faecalis of three basic patterns, which reflect different mechanisms leading to both the generation and depletion of initiators of the chemiluminescence, particularly hydrogen peroxide and superoxide radical. The influence of catalase and superoxide dismutase on the patterns was examined. We could demonstrate the sensitivity of chemiluminescence measurements for the detection of both exogenous oxidative stress, which is imposed to the cells by reactive species formed in the medium, as well as endogenous oxidative stress, which is due to products of the cellular oxygen metabolism, the latter being often the reason for growth restriction.

Production of nikkomycins Bx and Bz by mutasynthesis with genetically engineered Streptomyces tendae Tü901

The previously described Streptomyces tendae nikC::aph mutant was used to mutasynthesize nikkomycins Bx and Bz. The mutant is deficient in L-lysine 2-aminotransferase, which transaminates lysine to form piperideine 2-carboxylate, the precursor of the peptidyl side chain of the biologically active nikkomycins I, J, X, and Z, and is therefore unable to produce these nikkomycins. The mutant accumulates the biologically inactive biosynthetic nucleoside precursors nikkomycins Cx and Cz. Resting cell cultures of the mutant fed with benzoic acid produced the biologically active nikkomycins Bx and Bz, which contain 2-amino-4-hydroxy-3-methyl-4-(4'-hydroxyphenyl)butanoic acid as the peptidyl side chain. The structures of nikkomycins Bx and Bz were confirmed by mass spectrometry and NMR. Nikkomycins Bx and Bz exhibit significantly higher pH stability than their analogues nikkomycins X and Z.

Activation of nuclear factor-kappaB in macrophages by mycoplasmal lipopeptides

Mycoplasmas are potent macrophage stimulators. The active principle are lipopeptides or lipoproteins with a characteristic N-terminal S-[dihydroxypropyl]-cysteinyl group bearing two ester-bound fatty acids and lacking the amide-bound one common to other bacterial lipoproteins. Using synthetic analogues of mycoplasmal lipopeptides, we investigated activation of the transcription factor NF-kappaB in the C3H/HeJ mouse-derived DMBM-3 cell line. The lipopeptides activated NF-kappaB at below nanomolar concentrations. Activation in the murine system occurred distinctly earlier than TNF-alpha liberation, excluding autocrine stimulation by TNF-alpha. As determined from a supershift experiment, the active NF-kappaB complex consisted of the heterodimer p50/p65(RelA). The relevance of these findings for the inflammatory response to mycoplasmas and for mycoplasma-mediated effects on HIV-infected macrophages is discussed.

Structure and specific activity of macrophage-stimulating lipopeptides from Mycoplasma hyorhinis

Mycoplasmas are potent macrophage stimulators. We describe the isolation of macrophage-stimulatory lipopeptides S-[2, 3-bisacyl(C16:0/C18:0)oxypropyl]cysteinyl-GQTDNNSSQSQQPGS GTTNT and S-[2,3-bisacyl(C16:0/C18:0)oxypropyl]cysteinyl-GQTN derived from the Mycoplasma hyorhinis variable lipoproteins VlpA and VlpC, respectively. These lipopeptides were characterized by amino acid sequence and composition analysis and by mass spectrometry. The lipopeptides S-[2,3-bis(palmitoyloxy)propyl]cysteinyl-GQTNT and S-[2, 3-bis(palmitoyloxy)propyl]cysteinyl-SKKKK and the N-palmitoylated derivative of the latter were synthesized, and their macrophage-stimulatory activities were compared in a nitric oxide release assay with peritoneal macrophages from C3H/HeJ mice. The lipopeptides with the free amino terminus showed half-maximal activity at 3 pM regardless of their amino acid sequence; i.e., they were as active as the previously isolated M. fermentans-derived lipopeptide MALP-2. The macrophage-stimulatory activity of the additionally N-palmitoylated lipopeptide or of the murein lipoprotein from Escherichia coli, however, was lower by orders of magnitude. It is concluded that the lack of N-acyl groups in mycoplasmal lipoproteins explains their exceptionally high in vitro macrophage-stimulatory capacity. Certain features that lipopolysaccharide endotoxin and mycoplasmal lipopeptides have in common are discussed. Lipoproteins and lipopeptides are likely to be the main causative agents of inflammatory reactions to mycoplasmas. This may be relevant in the context of mycoplasmas as arthritogenic pathogens and their association with AIDS.

Characterization of the N-acetylglucosaminyltransferase activity involved in the biosynthesis of the Staphylococcus epidermidis polysaccharide intercellular adhesin

The polysaccharide intercellular adhesin (PIA) is an important factor in the colonization of medical devices by Staphylococcus epidermidis. The genes encoding PIA production are organized in the icaADBC (intercellular adhesion) operon. To study the function of the individual genes, we have established an in vitro assay with UDP-N-acetylglucosamine, the substrate for PIA biosynthesis, and analyzed the products by thin-layer chromatography and mass spectrometry. IcaA alone exhibited a low N-acetylglucosaminyltransferase activity and represents the catalytic enzyme. Coexpression of icaA with icaD led to a significant increase in activity. The newly identified icaD gene is located between icaA and icaB and overlaps both genes. N-Acetylglucosamine oligomers produced by IcaAD reached a maximal length of 20 residues. Only when icaA and icaD were expressed together with icaC were oligomer chains that react with PIA-specific antiserum synthesized. IcaA and IcaD are located in the cytoplasmic membrane, and IcaC also has all the structural features of an integral membrane protein. These results indicate a close interaction between IcaA, IcaD, and IcaC. Tunicamycin and bacitracin did not affect the in vitro synthesis of PIA intermediates or the complete PIA biosynthesis in vivo, suggesting that a undecaprenyl phosphate carrier is not involved. IcaAD represents a novel protein combination among beta-glycosyltransferases.

Bioassay guided isolation of a new C18-polyacetylene, (+)-9(Z),17-octadecadiene-12,14-diyne-1,11,16-triol, from Cassonia barteri

A novel C18-polyacetylene, (+)-9( Z),17-octadecadiene-12,14-diyne-1,11,16-triol, has been isolated from the ethyl acetate extract of Cassonia barteri (Araliaceae) leaves collected in Cameroon. The structure determination was achieved by NMR, mass, IR, and UV spectroscopy. The new polyenyne shows antibacterial activity against Bacillus subtilis and Pseudomonas fluorescens, antifungal activity against Cladosporium cucumerinum, moiluscicidal activity against Biomphalaria glabrata at low concentrations, and in addition it possesses haemolytic activity.

Structure of the pheromone peptide of the Staphylococcus epidermidis agr system

The agr quorum-sensing system is responsible for the regulation of several virulence factors in staphylococci, with an extracellular pheromone peptide as signalling molecule. By monitoring the biological activity of synthetic peptides, it could be demonstrated that the pheromone of the agr system in Staphylococcus epidermidis is an octapeptide containing a thiolester linkage between the central cysteine and the C-terminal carboxyl group. The peptide was active at nanomolar concentrations. The N-terminus of the peptide pheromone, which is encoded as part of a protein precursor, proved to be crucial for biological activity.

Adjuvant lipopeptide interaction with model membranes

The cationic lipohexapeptide Pam3Cys-Ser-(Lys)4 is a synthetic model for the triacylated N-terminal part of bacterial lipoproteins, and it is used as an adjuvant and macrophage activator. The amphiphilic lipopeptide was injected below a phosphatidylserine monolayer at the air-water interface. It interacted with the interface, as seen by a decrease in the surface potential (deltaV), and it was inserted in the monolayer, until surface charge neutralization was reached, as seen by the parallel increases of deltaV and of the surface pressure. No insertion occurred above 29 mN/m. The interaction kinetics was sensitive to ionic strength and to the nature of acidic phospholipids and of their acyl chains, but the final equilibrium was independent of these factors. Addition of the lipopeptide to large unilamellar vesicles (LUVs) induced their aggregation, and an exchange of lipids between fluorophor-labelled and non-labelled LUVs. However, no fusion was observed, just as reported for polylysine. The lipopeptide strongly inhibited calcium-induced fusion of PS LUVs, in contrast to the published effect of polylysine. This was probably due to inhibition of calcium fixation on liposomes, since it was observed that the lipopeptide efficiently displaced 45Ca2+ from a PS monolayer. In addition, a phospholipid segregation was observed in SUVs for a few ten micromolar of the lipopeptide.

Effect of salt concentration and temperature on survival of Legionella pneumophila

The effects of various concentrations of sodium chloride solutions (0.1%-3%) and different temperatures (4, 10, 20, 30 and 37 degrees C) on survival of Legionella pneumophila were investigated. It was found that at temperatures between 4 degrees C and 20 degrees C, Legionella organisms survived in salt solutions up to 3% NaCl. Only the combination of high temperatures, i.e. 30 degrees C and 37 degrees C, with NaCl concentrations over 1.5%, reduced cell numbers significantly. It was interesting to note that the addition of small amounts of NaCl (0.1%-0.5%) enhanced survival of Leg. pneumophila, suggesting a protective effect of NaCl. In order to obtain information about conditions encountered in the environment, the survival experiments were repeated in sterile sea water from the Baltic Sea and the North Sea. The marked bacterial die-off, especially at higher temperatures, was not observed in natural sea water. All these results indicate that Leg. pneumophila can survive in the marine environment.

Isolation, structure elucidation, and synthesis of a macrophage stimulatory lipopeptide from Mycoplasma fermentans acting at picomolar concentration

Macrophages are typically stimulated by components of microbial cell walls. Surprisingly, cell wall-less mycoplasmas can also very efficiently stimulate macrophages. We showed recently that mycoplasma-derived lipopeptides constitute the active principle. We have now isolated a clone of Mycoplasma fermentans expressing mainly one macrophage-stimulating lipopeptide. This lipopeptide was detergent-extracted and isolated by reversed-phase high-performance liquid chromotography, using nitric oxide release from C3H/HeJ mouse macrophages as bioassay for detection. In contrast to "conventional" bacterial lipoproteins, this lipopeptide had a free NH2 terminus. Amino acid composition, sequence, and the molecular weight of 2,163. 3 are consistent with the following structure: S-(2, 3-bisacyloxypropyl)cysteine-GNNDESNISFKEK with one mole C16:0, and a further mole of a mixture of C18:0 and C18:1 fatty acid per lipopeptide molecule. The sequence could not be found in either the protein identification resource nor the Swiss Prot data bank. We named this 2-kD lipopeptide, macrophage-activating lipopeptide-2 (MALP-2). Synthetic dipalmitoyl MALP-2 and mycoplasma-derived MALP-2 were compared with the bioassay. Both lipopeptides showed an identical dose dependency with a half-maximal response at 10(-11) M concentration. MALP-2 may be one of the most potent natural macrophage stimulators besides endotoxin.

Interaction between poly-3-hydroxybutyrate-co-3-hydroxyvalerate and a denitrifying Pseudomonas strain

In a laboratory-scale system, dentrification activity of a heterotrophic microbial starter culture changed when different lots of poly-3-hydroxybutyrate-co-3-hydroxyvalerate (P(HB-co-HV)) were used as the solid carbon source in the heterotrophic denitrification reactor. In this study, possible influences of physical and chemical properties of commercially produced P(HB-co-HV) (Biopol) on biofilm formation and metabolic activity of a denitrifying starter culture were investigated. These parameters indicate the polymers' suitability for the application as the matrix substance in the bioreactor. No differences in microstructure were detected between the different lots of polymers. Growth inhibitory effects by chemical additives were found in the case of triacetine, which was included as a plasticizer in seven of eight tested lots. The amount of hydroxyvaleric acid in the polymer was not assumed to affect denitrification activity. Relevant differences could be detected regarding primary adhesion of the starter culture Pseudomonas sp. strain 2nIII. It showed good adsorption properties to hydrophobic substances with a dependence on precultivation conditions. Pseudomonas sp. strain 2nIII degraded poly-3-hydroxybutyrate acid homopolymer and P(HB-co-HV) copolymers but was unable to break up poly-3-hydroxyvaleric acid. A possible reason for these findings is the substrate specifity of the polyhydroxyalkanoate depolymerase.

Site-directed mutagenesis of putative active-site residues in squalene-hopene cyclase

Squalene-hopene cyclase (SHC) catalyzes the complex polycylization of squalene to hopene, similar to the cyclization of oxidosqualene to sterols. Sequence analysis of SHC revealed a highly conserved aspartate-rich motif (DDTA), comparable to the DCTA motif of oxidosqualene cyclases, which is supposed to be part of the active site. In order to determine the importance of the motif in squalene cyclization, the conserved residues Asp376 and Asp377 in the DDTA motif of SHC from Alicyclobacillus acidocaldarius were individually replaced by glutamate, glutamine, glycine, and arginine. With the exception of the [Glu376]SHC mutant, all other substitutions resulted in almost or complete loss of enzyme activity. Compared to that of the wild-type enzyme, the specific activity of the [Glu376]SHC mutant enzyme was reduced to 10%, accompanied by a significant decrease in the apparent Vmax, whereas the apparent K(m) remained unchanged, CD measurements indicated that mutations did not affect the secondary structure. It is proposed that Asp376 and Asp377 are crucial for catalysis and may act as point charges to stabilize intermediate cations. Moreover, for squalene-hopene cyclase, a high content of alpha-helical conformation could be found, providing the first structural information for a triterpene cyclase.

Identification of gram-negative bacteria by isoelectric focusing of soluble cellular proteins

Strains of Escherichia coli, Pseudomonas aeruginosa and Proteus mirabilis, isolated from clinical specimens were disrupted by repeated freezing in liquid nitrogen and thawing at room temperature. The samples were separated by isoelectric focusing using polyacrylamide gels. The resulting protein patterns showed clear differences between the three species and made identification possible.

Swarming phenomena, basis of a method to identify motile bacteria densitometrically

The swarming phenomenon of 18 strains was tested with the intention to identify motile, swarming bacteria. Not all bacteria which are motile in liquid are able to swarm on semisolid nutrient broth, but all swarming bacteria show characteristic swarming developments, resulting in different swarming zones which could be scanned densitometrically. The densitograms are fully reproducible for the same strain and show similarities between strains of one species.

Proportion of phage-insensitive and phage-sensitive cells within pure strains of lactic streptococci, and the influence of calcium

It is of industrial importance to investigate the interaction ofStreptococcus lactiswith phages. Although it has been long recognized that in phage–bacterial relationships the phage-carrier state can occur (Hunter, 1947), relatively little study has been done on this subject. The terras ‘phage-carrier state’ and ‘pseudolysogeny’ have been used synonymously to describe bacterial cultures which are persistently infected with a virus (Barksdale & Arden, 1974, Lawrenceet al.1976). The phagecarrier state differs from lysogenesis in that the bacteria are easily separated from the bacteriophage by a simple plating and re-isolation procedure (Grahamet al.1952). Süssmuth & Tayran (1986) showed that after lysis of one single strain, phage and phage-insensitive bacteria coexist. This work investigates the proportion of phage-insensitive bacteria remaining after lysis of otherStr. lactisstrains, the effect of calcium on this proportion, and the number of generations required to return to a normal sensitive population.

A highly sensitive bacterial assay for toxins based on swarming inhibition, and comparison with the cup plate assay based on growth inhibition

The motility inhibition of the swarming bacteria Proteus mirabilis and Azospirillum brasilense was found to be an appropriate parameter to indicate toxic effects caused by some mycotoxins, lactones and anhydrides of dicarboxylic acids. If these substances are in contact with the motile bacteria the following phenomena can be observed: at a certain toxin concentration the swarming of the bacteria is inhibited. If the concentration is increased the swarming ceases, and at still higher concentrations the bacteria are inactivated. In some instances swarming is stimulated at very low toxin doses. The sensitivity of this assay is comparable to the cup plate assay based on growth inhibition with Bacillus thuringiensis [Lenz, P. et al., Toxicology, 40 (1986) 199, Boutibonnes et al., Pharmacology, 11 (1983) 430] and in some cases it is even higher.

Purification and characterization of chloramphenicol acetyltransferase from Flavobacterium CB60

From the highly chloramphenicol-resistant cytophaga-like bacterium Flavobacterium CB60, which can both acetylate chloramphenicol and degrade it in co-metabolism, the chloramphenicol acetyltransferase (CAT) was purified to homogeneity and characterized. The purification included fractional precipitation with ammonium sulphate and two affinity chromatography steps, eluting CAT the first time with 5 mM-chloramphenicol and the second time with a linear gradient (0-10 mM) of chloramphenicol. The purification was 3979-fold. Properties of this CAT were investigated and compared with CATs from other bacteria. Although CAT from Flavobacterium CB60 shares some properties with the enzymes from Escherichia coli and other Gram-negative bacteria--especially with CATII and CATIII--it has distinct properties like extreme heat lability and the inability to produce diacetylchloramphenicol, so that it might be regarded as a new variant.

Bacterial tests as indicators for the detoxification of the mycotoxin penicillic acid by ammonia treatment

The detoxification of penicillic acid by reaction with ammonia was examined by means of a polymerase assay using two strains of Escherichia coli (pol A+ and pol A-1) and a recombination assay using two strains of Bacillus subtilis (rec+ and rec-). A 100-fold surplus of ammonia added to penicillic acid abolished the cytotoxic and genotoxic effects of penicillic acid towards the bacteria under the test conditions. The study presents the possibility of detoxifying mycotoxins in feeds by ammonia treatment and demonstrates the suitability of bacterial assays as indicators for mycotoxins.

Development of sensitive bacterial tests, exemplified by two mycotoxins

For a sensitive bacterial test for mycotoxins the cup plate assay, based on growth inhibition, was optimised with Bacillus thuringiensis as test strain. Bacillus thuringiensis allowed the detection of 1.25 microgram kojic acid. A minimal amount of 12.5 micrograms kojic acid or 1.25 micrograms patulin was detectable by means of pigment suppression with isolated mutants of Serratia marcescens, whereas the wild type of this strain was insensitive.

Oscillating tolerance in synchronized cultures of Staphylococcus aureus

Cells of synchronized cultures of Staphylococcus aureus showed an oscillating MBC/MIC ratio when tested with penicillin G. Although the MICs did not differ significantly throughout the cell cycle, the MBC was at its maximum when actively dividing cells were inoculated.

The reaction of the mutagen 1,1'-hexamethylene-bis-[(5-p-chlorophenyl)-biguanide] with guanosine and cysteine

The mutagen 1,1'-hexamethylene-bis[(5-p-chlorophenyl)-biguanide] reacts at 37 degrees C with guanosine and guanine to yield xanthosine or xanthine and oxidizes cysteine to cystine. After treatment of a guanosine-labelled DNA sample from Escherichia coli with the mutagen xanthine could be detected as a reaction product. At a slow rate the mutagen is hydrolysed spontaneously yielding urea, 1.6-hexanediol and 4-chloroaniline. The reaction mechanisms both of the hydrolysis and of the reaction with cysteine and guanosine are discussed.

[Properties of aromatic-amino-acid aminotransferases from two chloramphenicol-resistant Flavobacteria]

Two enzymes of chloramphenicol-resistant Flavobacterium strain CB 60 and strain CB 6 which catalyse the transamination of tyrosine, phenylalanine and tryptophan were enriched 43-fold and 31-fold. The molecular mass for the aromatic-amino-acid aminotransferases of both strains was found to be 120000 Da and the isoelectric point was at about pH 4.2-4.3. Both enzymes are not influenced by EDTA. A ping pong bi-bi-mechanism was obtained for the kinetic mechanism of the reaction. The aminotransferases of strain CB 60 and CB 6 differ in the pH optimum (pH 8.4-9.0 and 7.8-9.0), in the optimum of temperature (40.0 degrees C and 57.5 degrees C) and in a higher heat stability of the enzyme of strain CB 60 in comparison to that of strain CB 6. The catalytic activity of the enzyme of strain CB 60 is not influenced by cycloserine, contrary to the enzyme of CB 6 which is inhibited to 89%. Isonicotinohydrazide does not inhibit the enzyme of strain CB 6, but reduces the catalytic activity of the enzyme of strain CB 60 to 64%. Both enzymes are inhibited differently by phenylhydrazine [78% (CB 60) and 56% (CB 6)]. Data in percentages are related to 0.15 mM inhibitor. For the substrates tyrosine, phenylalanine, tryptophan and 2-oxoglutarate, the aminotransferase of strain CB 60 has Km values of 15.0, 16.6, 16.6 and 1.7mM, and for the enzyme of strain CB 6 Km values of 1.40, 1.33, 1.37 and 0.97mM were obtained.

Effects of 1,1'-hexamethylene-bis-[(5-p-chlorophenyl)-biguanide] on the genome and on the synthesis of nucleic acids and proteins in the bacterial cells

The strongly effective bactericidal compound 1,1'-hexamethylene-bis-[(5-p-chlorophenyl)-biguanide] (HCG), which is used as a disinfectant alterates the DNA of B. subtilis as shown in the rec assay, induced auxotrophic mutants in E. coli B and causes prophage induction in Micrococcus lysodeikticus 53-40 (N5). In vivo experiments with E. coli B have demonstrated that HCG extensively breaks down bacterial DNA and interacts with the synthesis of cellular DNA to the similar extent as found for N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The structural integrity of ribosomes and of ribosomal subunits remains intact in the presence of HCG.

Conversion of chloramphenicol degradation products by tyrosine aminotransferase from Flavobacteria

The tyrosine aminotransferase of Flavobacterium strain CB 60, strain CB 6 and F. devorans r - a partially purified enzyme was used - is able to deaminate oxidatively p-aminophenylalanine and the intermediate products of chloramphenicol degradation p-nitrophenylserine and p-aminophenylserine. The aminotransferases of the strains CB 6 and CB 60 also convert p-aminophenylserinol. p-Nitrophenylserinol only reacts with the enzyme from strain CB 6. Determination of substrate specificity from strain CB 6 shows that an alcoholic group in C3 position (ring proximal) and to a lower degree an alcoholic group in C1 position (ring distal) decrease the turnover rate. Based on its broad substrate specificity the tyrosine aminotransferase has the ability not only to metabolize physiological compounds but also degradation products of chloramphenicol.

Induction of prophage and mutagenic effects by alkyl alkylaminosulfonates, ethyl aminosulfonate and alkyl methanesulfonates

Prophage induction and mutation by alkylaminosulfonates, ethyl aminosulfonate and alkyl methanesulfonates were examined comparatively. Prophage induction was carried out with a lysozyme lysis technique on the lysogenic strain Micrococcus lysodeikticus 53-40 (N5). The sulfonic ester derivatives show a slight lysogenic induction. At higher concentrations their toxicity seems to mask phage detection. Only methyl isopropylaminosulfonate and ethyl aminosulfonate exhibit no or negligible toxic effects, and with these compounds at higher concentrations a strong prophage induction is found. Alkyl sulfonate derivatives induce mutations in the tester strain of Salmonella typhimurium TA1535. Methyl methylaminosulfonate and ethyl N-methyl-N-2-chloroethyl aminosulfonate show a mutagenicity comparable to that of the well-known methyl methanesulfonate or ethyl methanesulfonate. With ethyl aminosulfonate, however, which does not show inactivation, no significant mutagenic effect was observed. DNA alterations were found in the polymerase-deficient strain E. coli P3478. The results of prophage induction and mutagenicity are compared and discussed.

Chloramphenicol resistance of three different flavobacteria

The chloramphenicol resistance of some flavobacteria was investigated comparatively. This resistance can be explained either by acetylation of chloramphenicol to O-acetylchloramphenicol via constitutively formed acetyltransferases, followed by cometabolic degradation (strain CB 60), or by limited uptake and total degradation (strain CB 6) by inducible enzymes or by other mechanisms (F. devorans). The mechanisms of resistance, CM-acetylation, CM-degradation and limited uptake are discussed.

[gamma-Irradiated ribosomes from Micrococcus radiodurans in a cell-free protein synthesizing system (author's transl)]

gamma-irradiation inactivation of isolated ribosomes of Micrococcus radiodurans was studied by examining poly U directed synthesis of polyphenylalanine. Ribosomes of M. radiodurans did not show significant gamma-radiation sensitivity up to a dose of approx. 11.6 k Gy. Cells of M. radiodurans take up more magnesium than E. coli cells unter the same conditions. The magnesium content of ribosomes of M. radiodurans was 18% higher than that of E. coli ribosomes. A possible relation between Mg2+-content and gamma-resistance is discussed.

[Protein synthesis with cell extracts of Micrococcus radiodurans (author's transl)]

Pure active ribosomes of cells of Micrococcus radiodurans could be obtained when cultivated in trypton, glucose and nutrient broth by adding natrium citrate. The optimal conditions for a cell-free protein synthesis were investigated at the (polyuridylic acid) dependent polyphenylalanine synthesis. When exchanging ribosomes and S100-fractions with the corresponding fractions of E. coli, we found that the enzyme fractions of M. radiodurans extremely inhibit the ribosomal activity. The incorporation rates in the cell-free system of M. radiodurans yield, at comparable conditions, in relation to E. coli under 10%.

Prophage induction by alkylating ethyl methylaminosulfonate

Treatment of the lysogenic strain M. lysodeikticus 53-40 (N5) with ethyl methylaminosulfonate results in a slight increase in infective center concentration of N5 phages which is only detectable once disturbing cells had been eliminated by lysozyme. After conversion of ethyl methylaminosulfonate with radioactive labelled guanosine at 37 degrees C, N7-ethyl-guanine could be ascertained. Therefore the biological activity of the drug may be due to an ethylation of DNA.