Detection of Dicrocoelium dendriticum larval stages in mollusc and ant intermediate hosts by PCR, using mitochondrial and ribosomal internal transcribed spacer (ITS-2) sequences.

The aim of this study was to develop, perfect and validate the PCR (polymerase chain reaction) technique using mitochondrial (mt) and ribosomal (ITS-2) DNA for the accurate identification of Dicrocoelium dendriticum in molluscs and ants, the first and second intermediate hosts, and their early detection. The first primers that were designed amplified a 169 pb mtDNA fragment of D. dendriticum permitted the detection of a single D. dendriticum metacercaria from the Formica rufibarbis and Formica pratensis abdomen, as well as the detection of the brainworm in the head of the ants collected in tetania. Although these primers did not amplify Dicrocoelium chinensis DNA and permitted detected D. dendriticum in the molluscs, they did not discriminate Brachylaimidae metacercariae found in the same mollusc. The PCR that was designed to amplify a 93 bp fragment of the ITS-2 is D. dendriticum specific as it did not amplify D. chinensis, Brachylaimidae and other trematodes. This technique is very sensitive since it permitted the detection of D. dendriticum in the molluscs from the first day post-infection, the brainworm in the head of the ants and only 1 D. dendriticum metacercaria from the abdomen of the ants. Both techniques are important, mainly the latter.

Partial characterization and isolation of 130 kDa antigenic protein of Dicrocoelium dendriticum adults.

The study focused on characterizing and isolating Dicrocoelium dendriticum antigens or their fractions that could be used for the immunological diagnosis of dicrocoeliosis. Somatic (SoAg) and excretory-secretory antigens (ESAg) were analyzed by SDS-PAGE and their specificity was evaluated by Western blot with homologous and heterologous sera. The antigens were partially purified by chromatographic techniques of gel-filtration (Sephacryl S-300) and ion exchange (Hitrap-DEAE-Sepharose). Western blot analysis using sera of ovine infected with D. dendriticum revealed eight main antigenic polypeptides ranging from 24 to 205 kDa for SoAg and seven for ESAg with apparent molecular mass in the range of 26-205 kDa. We detected a specific parasite protein with an approximate molecular weight of 130 kDa in SDS-PAGE gels, arranged as a 450 kDa tetramer in native conditions. It also showed strong immunoreactivity by Western blot against ovine sera experimentally infected with D. dendriticum. Gel filtration chromatography (Sephacryl S-300) also showed other specific proteins, one of about 24 kDa in SoAg and another of about 42 kDa in ESAg. The elution conditions of 450 kDa protein (130 kDa monomer) by DEAE chromatography were similar to those from the somatic antigen (pH 7.2, 0.1M NaCl, in 29-34 ml fractions) and from the excretion-secretion antigen (pH 8.0, 0.1M NaCl, in 29-35 ml fractions). The suitability of 130 kDa polypeptide for D. dendriticum infection diagnosis was confirmed by Western blot using a pool of sera as well as individual serum samples from experimentally infected sheep. The sequence of amino termini of 130 kDa polypeptide from both fractions was the same and identical to that reported for a peptide from D. dendriticum described as a globin. This sequence also revealed an appreciable similarity with the amino end of globins from some phylogenetically related worms.

Characterization of an inducible transport system for glycerol in Streptomyces clavuligerus. Repression by L-serine.

Streptomyces clavuligerus NRRL 3585 grown in a chemically defined medium containing glycerol as the sole carbon source transported this molecule by two different systems. One of these was constitutive with a very low uptake efficiency and insufficient to attend to the metabolic requirements of this bacterium (constitutive glycerol transport system) and the other (glycerol transport system (GTS)) active and specifically induced by D-glycerol which is responsible for the transport of more than 90% of the glycerol taken up the cells. GTS was seen to have an optimal pH and temperature of 7.0 and 30 degrees C, respectively, and its Km was 14 microM. It was repressed by L-serine and addition of this amino acid to the culture broth (10 mM) inhibited the growth of S. clavuligerus but not that of other species of Streptomyces.

Development and validation of a mtDNA multiplex PCR for identification and discrimination of Calicophoron daubneyi and Fasciola hepatica in the Galba truncatula snail.

Paramphistomosis and Fasciolosis caused by Calicophoron daubneyi and Fasciola hepatica, respectively, are frequent and important trematodoses in ruminant livestock worldwide. Both parasites use the same snail, Galba truncatula, as intermediate host. The aim of this study was to develop and validate an analytical method based on a mitochondrial DNA (mtDNA) multiplex PCR technique which would allow the early and specific identification, in one step, of C. daubneyi and F. hepatica infection in G. truncatula. First of all, a 1035 bp fragment of mtDNA from adult C. daubneyi worms was obtained. Then two pairs of specific mtDNA primers, which amplified a DNA fragment of 885 pb in the case of C. daubneyi, and of 425 pb in that of F. hepatica, were designed. By means of the multiplex PCR technique developed, there was always a specific amplification in samples from adult F. hepatica and C. daubneyi, but not from Calicophoron calicophorum, Cotylophoron cotylophorum, Cotylophoron batycotyle or Dicrocoelium dendriticum. Likewise, specific amplifications of the expected DNA fragments happened in all samples from snails harbouring larval stages of C. daubneyi or F. hepatica, previously detected by microscopy. However, amplifications were not seen when DNA from snails harbouring other Digenea (Plagiorchiidae, Notocotylidae and furcocercous cercariae) was analysed. Moreover, DNA from G. truncatula molluscs free from infection was not amplified. The multiplex PCR assay permitted infection in the snails experimentally infected with 4 miracidia to be detected as early as day 1 p.i. in the case of F. hepatica and with only 2 miracidia from day 2 p.i. in both, C. daubneyi and F. hepatica. Nevertheless it was necessary to wait until days 29 and 33 p.i. to see C. daubneyi and F. hepatica immature redia, respectively, using microscope techniques. The detection limit of the PCR technique was very low: 0.1 ng of DNA from C. daubneyi and 0.001 ng of DNA from F. hepatica. This allowed infection by either F. hepatica or C. daubneyi to be detected even when pools made up with only 1 µl (60 ng of DNA) from infected snail plus 99 µl from non-infected ones were analyzed. Moreover, simultaneous detection of both parasites was experimentally possible in pools made up with uninfected (98 µl), C. daubneyi infected (1 µl) and F. hepatica infected (1 µl) snails. The most precise and early diagnosis of the infections using the multiplex PCR technique designed will allow more realistic epidemiological models of both infections to be established and consequently a better strategic control.

A new class of glutamate dehydrogenases (GDH). Biochemical and genetic characterization of the first member, the AMP-requiring NAD-specific GDH of Streptomyces clavuligerus.

A new class of glutamate dehydrogenase (GDH) is reported. The GDH of Streptomyces clavuligerus was purified to homogeneity and characterized. It has a native molecular mass of 1,100 kDa and exists as an alpha(6) oligomeric structure composed of 183-kDa subunits. GDH, which requires AMP as an essential activator, shows a maximal rate of catalysis in 100 mm phosphate buffer, pH 7.0, at 30 degrees C. Under these conditions, GDH displayed hyperbolic behavior toward ammonia (K(m), 33 mm) and sigmoidal responses to changes in alpha-ketoglutarate (S(0.5) 1.3 mm; n(H) 1.50) and NADH (S(0.5) 20 microm; n(H) 1.52) concentrations. Aspartate and asparagine were found to be allosteric activators. This enzyme is inhibited by an excess of NADH or NH(4)(+), by some tricarboxylic acid cycle intermediates and by ATP. This GDH seems to be a catabolic enzyme as indicated by the following: (i) it is NAD-specific; (ii) it shows a high value of K(m) for ammonia; and (iii) when S. clavuligerus was cultured in minimal medium containing glutamate as the sole source of carbon and nitrogen, a 5-fold increase in specific activity of GDH was detected compared with cultures provided with glycerol and ammonia. GDH has 1,651 amino acids, and it is encoded by a DNA fragment of 4,953 base pairs (gdh gene). It shows strong sequence similarity to proteins encoded by unidentified open reading frames present in the genomes of species belonging to the genera Mycobacterium, Rickettsia, Pseudomonas, Vibrio, Shewanella, and Caulobacter, suggesting that it has a broad distribution. The GDH of S. clavuligerus is the first member of a class of GDHs included in a subfamily of GDHs (large GDHs) whose catalytic requirements and evolutionary implications are described and discussed.

From a short amino acidic sequence to the complete gene.

A useful strategy directed to the isolation of a required gene with a high GC content is reported. Using a degenerate oligonucleotide probe, deduced from the amino terminus of a protein, it is possible to obtain a fragment of DNA containing its encoding gene by PCR amplification. Furthermore, the cloning of a desired gene can be accomplished in two steps by using an oligonucleotide deduced (i) from an internal sequence, (ii) from a consensus sequence, or (iii) from a DNA sequence adjacent to a disrupting element (transposon, insertion sequence, cassette). This method, which could be applied to a bacteriophage, plasmid, or cosmid genomic library, has been successfully used for cloning several genes from different biological systems.

Phenylacetyl-coenzyme A is the true inducer of the phenylacetic acid catabolism pathway in Pseudomonas putida U.

Aerobic degradation of phenylacetic acid in Pseudomonas putida U is carried out by a central catabolism pathway (phenylacetyl-coenzyme A [CoA] catabolon core). Induction of this route was analyzed by using different mutants specifically designed for this objective. Our results revealed that the true inducer molecule is phenylacetyl-CoA and not other structurally or catabolically related aromatic compounds.

Catabolism of phenylacetic acid in Escherichia coli. Characterization of a new aerobic hybrid pathway.

The paa cluster of Escherichia coli W involved in the aerobic catabolism of phenylacetic acid (PA) has been cloned and sequenced. It was shown to map at min 31.0 of the chromosome at the right end of the mao region responsible for the transformation of 2-phenylethylamine into PA. The 14 paa genes are organized in three transcription units: paaZ and paaABCDEFGHIJK, encoding catabolic genes; and paaXY, containing the paaX regulatory gene. The paaK gene codes for a phenylacetyl-CoA ligase that catalyzes the activation of PA to phenylacetyl-CoA (PA-CoA). The paaABCDE gene products, which may constitute a multicomponent oxygenase, are involved in PA-CoA hydroxylation. The PaaZ protein appears to catalyze the third enzymatic step, with the paaFGHIJ gene products, which show significant similarity to fatty acid beta-oxidation enzymes, likely involved in further mineralization to Krebs cycle intermediates. Three promoters, Pz, Pa, and Px, driven the expression of genes paaZ, paaABCDEFGHIJK, and paaX, respectively, have been identified. The Pa promoter is negatively controlled by the paaX gene product. As PA-CoA is the true inducer, PaaX becomes the first regulator of an aromatic catabolic pathway that responds to a CoA derivative. The aerobic catabolism of PA in E. coli represents a novel hybrid pathway that could be a widespread way of PA catabolism in bacteria.

Microbial synthesis of poly(beta-hydroxyalkanoates) bearing phenyl groups from pseudomonas putida: chemical structure and characterization.

New poly(beta-hydroxyalkanoates) having aromatics groups (so-called PHPhAs) from a microbial origin have been characterized. These polymers were produced and accumulated as reserve materials when a beta-oxidation mutant of Pseudomonas putida U, disrupted in the gene that encodes the 3-ketoacyl-CoA thiolase (fadA), was cultured in a chemically defined medium containing different aromatic fatty acids (6-phenylhexanoic acid, 7-phenylheptanoic acid, a mixture of them, or 8-phenyloctanoic acid) as carbon sources. The polymers were extracted from the bacteria, purified and characterized by using (13)C nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Structural studies revealed that when 6-phenylhexanoic acid was added to the cultures, an homopolymer (poly-3-hydroxy-6-phenylhexanoate) was accumulated. The feeding with 8-phenyloctanoic acid and 7-phenylheptanoic acid leads to the formation of copolymers of the corresponding units with the n - 2 carbons formed after deacetylation, copoly(3-hydroxy-8-phenyloctanoate-3-hydroxy-6-phenylhexanoate) and copoly(3-hydroxy-7-phenylheptanoate-3-hydroxy-5-phenylvalerate), respectively. The mixture of 6-phenylhexanoic acid and 7-phenylheptanoic acid gave rise to the corresponding terpolymer, copoly(3-hydroxy-7-phenylheptanoate-3-hydroxy-6-phenylhexanoate-3-hydroxy-5-phenylvalerate). Studies on the chemical structure of these three polyesters revealed that they were true copolymers but not a mixture of homopolymers and that the different monomeric units were randomly incorporated in the macromolecular chains. Thermal behavior and molecular weight distribution were also discussed. These compounds had a dual attractive interest in function of (i) their broad use as biodegradable polymers and (ii) their possible biomedical applications.

Two different pathways are involved in the beta-oxidation of n-alkanoic and n-phenylalkanoic acids in Pseudomonas putida U: genetic studies and biotechnological applications.

In Pseudomonas putida U, the degradation of n-alkanoic and n-phenylalkanoic acids is carried out by two sets of beta-oxidation enzymes (betaI and betaII). Whereas the first one (called betaI) is constitutive and catalyses the degradation of n-alkanoic and n-phenylalkanoic acids very efficiently, the other one (betaII), which is only expressed when some of the genes encoding betaI enzymes are mutated, catabolizes n-phenylalkanoates (n > 4) much more slowly. Genetic studies revealed that disruption or deletion of some of the betaI genes handicaps the growth of P. putida U in media containing n-alkanoic or n-phenylalkanoic acids with an acyl moiety longer than C4. However, all these mutants regained their ability to grow in media containing n-alkanoates as a result of the induction of betaII, but they were still unable to catabolize n-phenylalkanoates completely, as the betaI-FadBA enzymes are essential for the beta-oxidation of certain n-phenylalkanoyl-CoA derivatives when they reach a critical size. Owing to the existence of the betaII system, mutants lacking betaIfadB/A are able to synthesize new poly 3-OH-n-alkanoates (PHAs) and poly 3-OH-n-phenylalkanoates (PHPhAs) efficiently. However, they are unable to degrade these polymers, becoming bioplastic overproducer mutants. The genetic and biochemical importance of these results is reported and discussed.

Molecular cloning and expression in different microbes of the DNA encoding Pseudomonas putida U phenylacetyl-CoA ligase. Use of this gene to improve the rate of benzylpenicillin biosynthesis in Penicillium chrysogenum.

The gene encoding phenylacetyl-CoA ligase (pcl), the first enzyme of the pathway involved in the aerobic catabolism of phenylacetic acid in Pseudomonas putida U, has been cloned, sequenced, and expressed in two different microbes. In both, the primary structure of the protein was studied, and after genetic manipulation, different recombinant proteins were analyzed. The pcl gene, which was isolated from P. putida U by mutagenesis with the transposon Tn5, encodes a 48-kDa protein corresponding to the phenylacetyl-CoA ligase previously purified by us (Martínez-Blanco, H., Reglero, A. Rodríguez-Aparicio, L. B., and Luengo, J. M. (1990) J. Biol. Chem. 265, 7084-7090). Expression of the pcl gene in Escherichia coli leads to the appearance of this enzymatic activity, and cloning and expression of a 10.5-kb DNA fragment containing this gene confer this bacterium with the ability to grow in chemically defined medium containing phenylacetic acid as the sole carbon source. The appearance of phenylacetyl-CoA ligase activity in all of the strains of the fungus Penicillium chrysogenum transformed with a construction bearing this gene was directly related to a significant increase in the quantities of benzylpenicillin accumulated in the broths (between 1.8- and 2.2-fold higher), indicating that expression of this bacterial gene (pcl) helps to increase the pool of a direct biosynthetic precursor, phenylacetyl-CoA. This report describes the sequence of a phenylacetyl-CoA ligase for the first time and provides direct evidence that the expression in P. chrysogenum of a heterologous protein (involved in the catabolism of a penicillin precursor) is a useful strategy for improving the biosynthetic machinery of this fungus.

Novel biodegradable aromatic plastics from a bacterial source. Genetic and biochemical studies on a route of the phenylacetyl-coa catabolon.

Novel biodegradable bacterial plastics, made up of units of 3-hydroxy-n-phenylalkanoic acids, are accumulated intracellularly by Pseudomonas putida U due to the existence in this bacterium of (i) an acyl-CoA synthetase (encoded by the fadD gene) that activates the aryl-precursors; (ii) a beta-oxidation pathway that affords 3-OH-aryl-CoAs, and (iii) a polymerization-depolymerization system (encoded in the pha locus) integrated by two polymerases (PhaC1 and PhaC2) and a depolymerase (PhaZ). The complete assimilation of these compounds requires two additional routes that specifically catabolize the phenylacetyl-CoA or the benzoyl-CoA generated from these polyesters through beta-oxidation. Genetic studies have allowed the cloning, sequencing, and disruption of the genes included in the pha locus (phaC1, phaC2, and phaZ) as well as those related to the biosynthesis of precursors (fadD) or to the catabolism of their derivatives (acuA, fadA, and paa genes). Additional experiments showed that the blockade of either fadD or phaC1 hindered the synthesis and accumulation of plastic polymers. Disruption of phaC2 reduced the quantity of stored polymers by two-thirds. The blockade of phaZ hampered the mobilization of the polymer and decreased its production. Mutations in the paa genes, encoding the phenylacetic acid catabolic enzymes, did not affect the synthesis or catabolism of polymers containing either 3-hydroxyaliphatic acids or 3-hydroxy-n-phenylalkanoic acids with an odd number of carbon atoms as monomers, whereas the production of polyesters containing units of 3-hydroxy-n-phenylalkanoic acids with an even number of carbon atoms was greatly reduced in these bacteria. Yield-improving studies revealed that mutants defective in the glyoxylic acid cycle (isocitrate lyase(-)) or in the beta-oxidation pathway (fadA), stored a higher amount of plastic polymers (1.4- and 2-fold, respectively), suggesting that genetic manipulation of these pathways could be useful for isolating overproducer strains. The analysis of the organization and function of the pha locus and its relationship with the core of the phenylacetyl-CoA catabolon is reported and discussed.

Molecular characterization of the phenylacetic acid catabolic pathway in Pseudomonas putida U: the phenylacetyl-CoA catabolon.

Fourteen different genes included in a DNA fragment of 18 kb are involved in the aerobic degradation of phenylacetic acid by Pseudomonas putida U. This catabolic pathway appears to be organized in three contiguous operons that contain the following functional units: (i) a transport system, (ii) a phenylacetic acid activating enzyme, (iii) a ring-hydroxylation complex, (iv) a ring-opening protein, (v) a beta-oxidation-like system, and (vi) two regulatory genes. This pathway constitutes the common part (core) of a complex functional unit (catabolon) integrated by several routes that catalyze the transformation of structurally related molecules into a common intermediate (phenylacetyl-CoA).

Genetically engineered Pseudomonas: a factory of new bioplastics with broad applications.

New bioplastics containing aromatic or mixtures of aliphatic and aromatic monomers have been obtained using genetically engineered strains of Pseudomonas putida. The mutation (-) or deletion (Delta) of some of the genes involved in the beta-oxidation pathway (fadA(-), fadB(-) Delta fadA or Delta fad BA mutants) elicits a strong intracellular accumulation of unusual homo- or co-polymers that dramatically alter the morphology of these bacteria, as more than 90% of the cytoplasm is occupied by these macromolecules. The introduction of a blockade in the beta-oxidation pathway, or in other related catabolic routes, has allowed the synthesis of polymers other than those accumulated in the wild type (with regard to both monomer size and relative percentage), the accumulation of certain intermediates that are rapidly catabolized in the wild type and the accumulation in the culture broths of end catabolites that, as in the case of phenylacetic acid, phenylbutyric acid, trans-cinnamic acid or their derivatives, have important medical or pharmaceutical applications (antitumoral, analgesic, radiopotentiators, chemopreventive or antihelmintic). Furthermore, using one of these polyesters (poly 3-hydroxy-6-phenylhexanoate), we obtained polymeric microspheres that could be used as drug vehicles.