Novel beta-lactam antibiotics synthesized by amination of catechols using fungal laccase

Novel cephalosporins, penicillins, and carbacephems were synthesized by amination of catechols with amino-beta-lactams like cefadroxil, amoxicillin, ampicillin and the structurally related carbacephem loracarbef using laccase from Trametes sp. All isolated monoaminated products inhibited the growth of several Gram positive bacterial strains in the agar diffusion assay, among them methicillin-resistant Staphylococcus aureus strains and vancomycin-resistant Enterococci. Observed differences in the cytotoxicity and in vivo activity in a "Staphylococcus-infected, immune suppressed mouse" model are discussed.

Laccase-catalyzed carbon-nitrogen bond formation: coupling and derivatization of unprotected L-phenylalanine with different para-hydroquinones

Unprotected L-phenylalanine was derivatized by an innovative enzymatic method by means of laccases from Pycnoporus cinnabarinus and Myceliophthora thermophila. During the incubation of L-phenylalanine with para-hydroquinones using laccase as biocatalyst, one or two main products were formed. Dependent on the substitution grade of the hydroquinones mono- and diaminated products were detected. Differences of the used laccases are discussed. The described reactions are of interest for the derivatization of amino acids and a synthesis of pharmacological-active amino acid structures in the field of white biotechnology.

Laccase-induced C-N coupling of substituted p-hydroquinones with p-aminobenzoic acid in comparison with known chemical routes

Fungal laccases (benzenediol:oxygen oxidoreductase, EC 1.10.3.2) from Pycnoporus cinnabarinus and Myceliophthora thermophila were used as biocatalysts for enzymatic reaction of halogen-, alkyl-, alkoxy-, and carbonyl-substituted p-hydroquinones (laccase substrates) with p-aminobenzoic acid (no laccase substrate). During this reaction, the laccase substrate was oxidized to the corresponding quinones, which react with p-aminobenzoic acid by amination of the laccase substrate. The different substitutions at the hydroquinone substrates were used to prove whether the substituents influence the position of amination and product yields. The cross-coupling of methoxy-p-hydroquinone (alkoxylated) and 2,5-dihydroxybenzaldehyd (carbonyl-substituted) with p-aminobenzoic acid resulted in the formation of one monoaminated product (yield alkoxylated 52%). If monohalogen- or monoalkyl-substituted p-hydroquinones were used as laccase substrates, two monoaminated products (constitution isomers) were formed. The simultaneous formation of two different monoaminated products from the same hydroquinone substrate is the first report for laccase-mediated synthesis of aminated constitution isomers. Depending from the type of substituent of the hydroquinone, the positions of the two monoaminations are different. While the amination at the monoalkylated hydroquinone occurs at the 5- and 6-positions (yield 38%), the amination at monohalogenated hydroquinones was detectable at the 3- and 5-positions (yield 53%). The same product pattern could be achieved if instead of the biocatalyst laccase the chemical catalyst sodium iodate was used as the oxidant. However, the yields were partially much lower (0-45% of the yields with laccase).

Anaerobically grown Thauera aromatica, Desulfococcus multivorans, Geobacter sulfurreducens are more sensitive towards organic solvents than aerobic bacteria

The effect of seven important pollutants and three representative organic solvents on growth of Thauera aromatica K172, as reference strain for nitrate-reducing anaerobic bacteria, was investigated. Toxicity in form of the effective concentrations (EC50) that led to 50% growth inhibition of potential organic pollutants such as BTEX (benzene, toluene, ethylbenzene, and xylene), chlorinated phenols and aliphatic alcohols on cells was tested under various anaerobic conditions. Similar results were obtained for Geobacter sulfurreducens and Desulfococcus multivorans as representative for Fe(3+)-reducing and sulphate-reducing bacteria, respectively, leading to a conclusion that anaerobic bacteria are far more sensitive to organic pollutants than aerobic ones. Like for previous studies for aerobic bacteria, yeast and animal cell cultures, a correlation between toxicity and hydrophobicity (log P values) of organic compounds for different anaerobic bacteria was ascertained. However, compared to aerobic bacteria, all three tested anaerobic bacteria were shown to be about three times more sensitive to the tested substances.

Novel cephalosporins synthesized by amination of 2,5-dihydroxybenzoic acid derivatives using fungal laccases II

Sixteen novel cephalosporins were synthesized by amination of 2,5-dihydroxybenzoic acid derivatives with the aminocephalosporins cefadroxil, cefalexin, cefaclor, and the structurally related carbacephem loracarbef using laccases from Trametes sp. or Myceliophthora thermophila. All products inhibited the growth of several Gram positive bacterial strains in the agar diffusion assay, among them methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. The products protected mice against an infection with Staphylococcus aureus lethal to the control animals. Cytotoxicity and acute toxicity of the new compounds were negligible. The results show the usefulness of laccase for the synthesis of potential new antibiotics. The biological activity of the new compounds stimulates intensified pharmacological tests.

Carbon-oxygen bond formation by fungal laccases: cross-coupling of 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide with the solvents water, methanol, and other alcohols

Laccase-catalyzed reactions lead to oxidation of the substrate via a cation radical, which has been described to undergo proton addition to form a quinonoid derivative or nucleophilic attack by itself producing homomolecular dimers. In this study, for the substrate 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide, we show that, besides the quinonoid form of substrate, all products formed are nonhomomolecular ones. Indeed, without addition of a reaction partner, heteromolecular products are formed from the quinonoid form of the laccase-substrate and the solvents water or methanol present in the incubation assay. Consequently, in laccase catalyzed syntheses performed in aqueous solutions or in the presence of methanol or other alcohols, undesirable heteromolecular coupling reactions between the laccase substrate and solvents must be taken into account. Additionally, it could be shown at the example of methanol and other alcohols that C-O-bound cross-coupling of dihydroxylated aromatic substances with the hydroxyl group of aliphatic alcohols can be catalyzed by fungal laccases.

Ultraviolet photoinduced weak bonds in aryl-substituted polysilanes

The susceptibility of aryl-substituted polysilylenes to photodegradation by ultraviolet (UV) radiation is examined on the prototypical materials poly[methyl(phenyl)silylene] (PMPSi) and poly[(biphenyl-4-yl)methylsilylene] (PBMSi). We extend the scope of our last paper (Schauer et al 2004 Polym. Degrad. Stabil. 84 383) with the elucidation of the degradation mechanisms for two different degradation wavelengths: 266 and 355 nm. The main purpose of this paper was to study photoluminescence (PL) after major degradation, predominantly in long-wavelength range 400-600 nm, studying the disorder, dangling bonds (DBs) and weak bonds (WBs) created by the degradation process. We claim that the PL of the 500-600 nm band is related to the existence of WBs on the Si chain and originates in the σ(*)-σ exciton migration at room temperature by diffusion, free electron-hole formation, trapping in WBs and subsequent radiative recombination by tunnelling. Increase of the normalized PL 520-540 nm band after UV degradation can be then evaluated as the increase of the density of states (DOS) of WBs. The efficiency of the WB creation in PMPSi is greater for 266 nm irradiation, supporting the notion of the suppressed exciton transport compared to the less energetical photon of 355 nm, where the WB creation is lowered due to the exciton migration to longer segments and/or already existing defects. For PBMSi the WB creation kinetics for 355 nm degradation is similar to that of PMPSi. The 266 nm degradation results then support the model calculations of DB and WB reconstruction in the more rigid Si skeleton.

High level expression of a recombinant phospholipase C from Bacillus cereus in Bacillus subtilis

Twenty-two Bacillus cereus strains were screened for phospholipase C (PLC, EC 3.1.4.3) activity using p-nitrophenyl phosphorylcholine as a substrate. Two strains (B. cereus SBUG 318 and SBUG 516) showed high activity at elevated temperatures (>70 degrees C) at acidic pH (pH 3.5-6) and were selected for cloning and functional expression using Bacillus subtilis. The genes were amplified from B. cereus DNA using primers based on a known PLC sequence and cloned into the expression vector pMSE3 followed by transformation into B. subtilis WB800. On the amino acid level, one protein (PLC318) was identical to a PLC described from B. cereus, whereas PLC516 contained an amino acid substitution (E173D). PLC production using the recombinant strains was performed by an acetoin-controlled expression system. For PLC516, 13.7 U g(-1) wet cell weight was determined in the culture supernatant after 30 h cultivation time. Three purification steps resulted in pure PLC516 with a specific activity of 13,190 U mg(-1) protein.

Differential gene expression in response to phenol and catechol reveals different metabolic activities for the degradation of aromatic compounds in Bacillus subtilis

Aromatic organic compounds that are present in the environment can have toxic effects or provide carbon sources for bacteria. We report here the global response of Bacillus subtilis 168 to phenol and catechol using proteome and transcriptome analyses. Phenol induced the HrcA, sigmaB and CtsR heat-shock regulons as well as the Spx disulfide stress regulon. Catechol caused the activation of the HrcA and CtsR heat-shock regulons and a thiol-specific oxidative stress response involving the Spx, PerR and FurR regulons but no induction of the sigmaB regulon. The most surprising result was that several catabolite-controlled genes are derepressed by catechol, even if glucose is taken up under these conditions. This derepression of the carbon catabolite control was dependent on the glucose concentration in the medium, as glucose excess increased the derepression of the CcpA-dependent lichenin utilization licBCAH operon and the ribose metabolism rbsRKDACB operon by catechol. Growth and viability experiments with catechol as sole carbon source suggested that B. subtilis is not able to utilize catechol as a carbon-energy source. In addition, the microarray results revealed the very strong induction of the yfiDE operon by catechol of which the yfiE gene shares similarities to glyoxalases/bleomycin resistance proteins/extradiol dioxygenases. Using recombinant His6-YfiE(Bs) we demonstrate that YfiE shows catechol-2,3-dioxygenase activity in the presence of catechol as the metabolite 2-hydroxymuconic semialdehyde was measured. Furthermore, both genes of the yfiDE operon are essential for the growth and viability of B. subtilis in the presence of catechol. Thus, our studies revealed that the catechol-2,3-dioxygenase YfiE is the key enzyme of a meta cleavage pathway in B. subtilis involved in the catabolism of catechol.

Novel penicillins synthesized by biotransformation using laccase from Trametes spec

Eight novel penicillins were synthesized by heteromolecular reaction of ampicillin or amoxicillin with 2,5-dihydroxybenzoic acid derivatives using a laccase from Trametes spec. All products inhibited the growth of several gram positive bacterial strains in the agar diffusion assay, among them methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci. The products protected mice against an infection with Staphylococcus aureus lethal to the untreated animals. Cytotoxicity and acute toxicity of the new compounds were neglectable. The results show the usefulness of laccase for the synthesis of potential new antibiotics. The biological activity of the new compounds stimulates intensified pharmacological tests.

Oxidative ring cleavage of low chlorinated biphenyl derivatives by fungi leads to the formation of chlorinated lactone derivatives

The yeast Trichosporon mucoides and the filamentous fungus Paecilomyces lilacinus as biphenyl oxidizing organisms are able to oxidize chlorinated biphenyl derivatives. Initial oxidation of derivatives chlorinated at C4 position started at the non-halogenated ring and went on up to ring cleavage. The products formed were mono- and dihydroxylated 4-chlorobiphenyls, muconic acid derivatives 2-hydroxy-4-(4-chlorophenyl)-muconic acid and 2-hydroxy-5-(4-chlorophenyl)-muconic acid as well as the corresponding lactones 4-(4-chlorophenyl)-2-pyrone-6-carboxylic acid and 3-(4-chlorophenyl)-2-pyrone-6-carboxylic acid. Altogether T. mucoides formed 12 products and P. lilacinus accumulated five products. Whereas the rate of the first oxidation step at 4-chlorobiphenyl seems to be diminished by the decreased bioavailability of the compound, no considerable differences were observed between the degradation of 4-chloro-4'-hydroxybiphenyl and 4-hydroxybiphenyl. Twofold chlorinated biphenyl derivatives did not serve as substrates for oxidation by either organism with the exception of 2,2'-dichlorobiphenyl, transformed by the yeast Trichosporon mucoides to two monohydroxylated derivatives. The results show, that soil fungi may contribute to the aerobic degradation of low chlorinated biphenyls accumulating from anaerobic dehalogenation of PCB by bacteria.

Laccase-induced derivatization of unprotected amino acid L-tryptophan by coupling with p-hydroquinone 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide

We have studied the enzymatic derivatization of amino acids by use of the polyphenol oxidase laccase. Derivatization of L-tryptophan was achieved by enzymatic crosslinking with the laccase substrate 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide. The main product (yield up to 70%) was identified as the quinoid compound 2-[2-(2-hydroxy-ethylcarbamoyl)-3,6-dioxo-cyclohexa-1,4-dienylamino]-3-(1H-indol-3-yl)- propionic acid and demonstrates that laccase-catalyzed C-N-coupling occurred on the amino group of the aliphatic side chain. These enzyme based reactions provide a simple and fast method for the derivatization of unprotected amino acids.

Transformation of 2-hydroxydibenzofuran by laccases of the white rot fungi Trametes versicolor and Pycnoporus cinnabarinus and characterization of oligomerization products

Laccase, a ligninolytic enzyme, was secreted by each of the white rot fungi Trametes versicolor and Pycnoporus cinnabarinus during growth in a nitrogen-rich medium under agitated conditions. After addition of 2-hydroxydibenzofuran to cell-free supernatants of the cultures, yellow precipitates were formed. These precipitates were poorly soluble in water and therefore readily separated from the supernatant. The products formed were more hydrophobic than the substrate, as indicated by their longer retention times on a reverse phase high-performance liquid chromatography column. Mass spectrometric analysis of the purified products indicated the formation of oligomers. Analysis of the mixture of products by gas chromatography and mass spectrometry after derivatization with diazomethane suggested the formation of at least three dimeric and nine trimeric products. Carbon-carbon and carbon-oxygen bonds were identified in the dimers and trimers, respectively. The nuclear magnetic resonance spectrum of the main dimer suggested coupling of the two monomers at the carbon one position.

The bphC gene-encoded 2,3-dihydroxybiphenyl-1,2-dioxygenase is involved in complete degradation of dibenzofuran by the biphenyl-degrading bacterium Ralstonia sp. SBUG 290

AIMS

Biphenyl-degrading bacteria are able to metabolize dibenzofuran via lateral dioxygenation and meta-cleavage of the dihydroxylated dibenzofuran produced. This degradation was considered to be incomplete because accumulation of a yellow-orange ring-cleavage product was observed. In this study, we want to characterize the 1,2-dihydroxydibenzofuran cleaving enzyme which is involved in dibenzofuran degradation in the bacterium Ralstonia sp. SBUG 290.

METHODS AND RESULTS

In this strain, complete degradation of dibenzofuran was observed after cultivation on biphenyl. The enzyme shows a wide substrate utilization spectrum, including 1,2-dihydroxydibenzofuran, 2,3-dihydroxybiphenyl, 1,2-dihydroxynaphthalene, 3- and 4-methylcatechol and catechol. MALDI-TOF analysis of the protein revealed a strong homology to the bphC gene products. We therefore cloned a 3.2 kb DNA fragment containing the bphC gene of Ralstonia sp. SBUG 290. The deduced amino acid sequence of bphC is identical to that of the corresponding gene in Pseudomonas sp. KKS102. The bphC gene was expressed in Escherichia coli and the meta-fission activity was detected using either 2,3-dihydroxybiphenyl or 1,2-dihydroxydibenzofuran as substrate.

CONCLUSIONS

These results demonstrate that complete degradation of dibenzofuran by biphenyl degraders can occur after initial oxidation steps catalysed by gene products encoded by the bph-operon. The ring fission of 1,2-dihydroxydibenzofuran is catalysed by BphC. Differences found in the metabolism of the ring fission product of dibenzofuran among biphenyl degrading bacteria are assumed to be caused by different substrate specificities of BphD.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows for the first time that the gene products of the bph-operon are involved in the mineralization of dibenzofuran in biphenyl degrading bacteria.

Simultaneous degradation of atrazine and phenol by Pseudomonas sp. strain ADP: effects of toxicity and adaptation

The strain Pseudomonas sp. strain ADP is able to degrade atrazine as a sole nitrogen source and therefore needs a single source for both carbon and energy for growth. In addition to the typical C source for Pseudomonas, Na(2)-succinate, the strain can also grow with phenol as a carbon source. Phenol is oxidized to catechol by a multicomponent phenol hydroxylase. Catechol is degraded via the ortho pathway using catechol 1,2-dioxygenase. It was possible to stimulate the strain in order to degrade very high concentrations of phenol (1,000 mg/liter) and atrazine (150 mg/liter) simultaneously. With cyanuric acid, the major intermediate of atrazine degradation, as an N source, both the growth rate and the phenol degradation rate were similar to those measured with ammonia as an N source. With atrazine as an N source, the growth rate and the phenol degradation rate were reduced to approximately 35% of those obtained for cyanuric acid. This presents clear evidence that although the first three enzymes of the atrazine degradation pathway are constitutively present, either these enzymes or the uptake of atrazine is the bottleneck that diminishes the growth rate of Pseudomonas sp. strain ADP with atrazine as an N source. Whereas atrazine and cyanuric acid showed no significant toxic effect on the cells, phenol reduces growth and activates or induces typical membrane-adaptive responses known for the genus Pseudomonas. Therefore Pseudomonas sp. strain ADP is an ideal bacterium for the investigation of the regulatory interactions among several catabolic genes and stress response mechanisms during the simultaneous degradation of toxic phenolic compounds and a xenobiotic N source such as atrazine.

Oxidation and ring cleavage of dibenzofuran by the filamentous fungus Paecilomyces lilacinus

The ability of the imperfect soil fungus Paecilomyces lilacinus to transform the environmental pollutant dibenzofuran was investigated. Transformation of dibenzofuran and related derivatives lead to 14 products, which were identified by UV spectroscopy, mass spectrometry, and proton nuclear magnetic resonance spectroscopy. Biotransformation was initiated by two separate hydroxylation steps, leading to the accumulation of 4-monohydroxylated and 4-dihydroxylateddibenzofurans. Hydroxylation at both aromatic rings produced 2,7-dihydroxydibenzofuran, 3,7-dihydroxydibenzofuran, and 2,8-dihydroxydibenzofuran. Further oxidation yields ring cleavage of dibenzofuran, which has not been described before for filamentous fungi. The ring fission products were identified as benzo[ b]furo[3,2-d]-2-pyrone-6-carboxylic acid and [2-(1-carboxy-methylidene)-benzofuran-3-ylidene]-hydroxy-acetic acid and its derivatives hydroxylated at carbon 7 and 8 at the non-cleaved ring. Other metabolites were riboside-conjugates of 2-hydroxydibenzofuran and 3-hydroxydibenzofuran. The results showed that P. lilacinus transforms the hydrophobic compound dibenzofuran by phase I/phase II reactions to produce hydroxylated products and excretable sugar conjugates.