Bioaugmented sulfur-oxidizing denitrification system with Alcaligenes defragrans B21 for high nitrate containing wastewater treatment

The performance of enriched sludge augmented with the B21 strain of Alcaligenes defragrans was compared with that of enriched sludge, as well as with pure Alcaligenes defragrans B21, in the context of a sulfur-oxidizing denitrification (SOD) process. In synthetic wastewater treatment containing 100-1,000 mg NO3-N/L, the single strain-seeded system exhibited superior performance, featuring higher efficiency and a shorter startup period, provided nitrate loading rate was less than 0.2 kg NO3-N/m(3) per day. At nitrate loading rate of more than 0.5 kg NO3-N/m(3) per day, the bioaugmented sludge system showed higher resistance to shock loading than two other systems. However, no advantage of the bioaugmented system over the enriched sludge system without B21 strain was observed in overall efficiency of denitrification. Both the bioaugmented sludge and enriched sludge systems obtained stable denitrification performance of more than 80% at nitrate loading rate of up to 2 kg NO3-N/m(3) per day.

Coordinate synthesis of azurin I and copper nitrite reductase in Alcaligenes xylosoxidans during denitrification

The denitrifying bacterium Alcaligenes xylosoxidans synthesises two azurins (Az), which are termed Az I and Az 2. Both function as effective electron donors to copper nitrite reductase (NiR) in vitro. As a first step towards identifying the physiological relevance of these electron transfer proteins in the denitrification process, the gene (azuA) encoding Az I was characterised and its expression with respect to denitrification determined. We show that the azuA gene from A. xylosoxidans is monocistronic and its expression is increased when cells are grown under denitrifying conditions in the presence of nitrate or nitrite. The expression pattern of azuA was similar, though not identical, to that of the monocistronic nirK gene, which encodes copper NiR, and is in accord with both gene products being synthesised when the bacterium denitrifies. Recombinant Az I was exported to the periplasm of the heterologous host Escherichia coli, was synthesised at very high levels (80 mg purified protein per litre) and was fully loaded with copper. Electron donation from reduced recombinant Az to NiR was indistinguishable from the activity determined with the native protein. Taken together, these findings indicate that in A. xylosoxidans azuA expression is coordinated with denitrification and recombinant Az I is processed and matured in the periplasm of E. coli in the same way it is in A. xylosoxidans.

Metabolism of [14C]-2,4-dichlorophenol in edible plants

Several 2,4-dichlorophenoxyacetic acid (2,4-D)-sensitive plants have been modified by genetic engineering with tfdA gene to acquire 2,4-D tolerance. The expression product of this gene degrades 2,4-D to 2,4-dichlorophenol (DCP), which is less phytotoxic but could cause a problem of food safety. After a comparison of 2,4-D and DCP metabolism in transgenic 2,4-D-tolerant and wild cotton (Gossypium hirsutum L.), a direct study of DCP metabolism in edible plants was performed. After petiolar uptake of a [U-phenyl-(14)C]-DCP solution followed by a 48 h water chase, aqueous extracts were analysed by high-performance liquid chromatography. Metabolites were thereafter isolated and their structural identities were determined by enzymatic and chemical hydrolyses and mass spectrometry analyses. The metabolic fate of DCP was equivalent to 2,4-D metabolism in transgenic 2,4-D-tolerant cotton. In addition, DCP metabolism was similar in transgenic and wild cotton. The major terminal metabolites were DCP-saccharide conjugates in all species, essentially DCP-(6-O-malonyl)-glucoside or its precursor DCP-glucose. The significance of this metabolic pathway with regard to food safety is discussed.

Alcaligenes aquatilis sp. nov., a novel bacterium from sediments of the Weser Estuary, Germany, and a salt marsh on Shem Creek in Charleston Harbor, USA

Four nitrite-dissimilating strains, isolated from Weser Estuary sediments, were investigated using a polyphasic taxonomic approach. Phylogenetic analysis based on 16S rRNA gene sequences indicated that these strains belong to the 'Betaproteobacteria' and are related to the genus Alcaligenes. The highest level of sequence similarity (100 %) was found with strain M3A (=ATCC 700596), a dimethyl sulfide-producing marine isolate that was included in this study. DNA-DNA hybridizations between the five strains and related Alcaligenes faecalis strains confirmed that the former belong to a single and novel species within the genus Alcaligenes. The isolates are Gram-negative, motile, rod-shaped cells with a DNA G+C content of about 56 mol%. The whole-cell fatty acid profiles of the isolates were very similar and included C(16 : 0), C(17 : 0) cyclo, C(18 : 1)omega7c, summed feature 2 (comprising any combination of C(12 : 0) aldehyde, an unknown fatty acid of equivalent chain length 10.928, C(16 : 1) iso I and C(14 : 0) 3-OH) and summed feature 3 (C(15 : 0) iso 2-OH and/or C(16 : 1)omega7c) as the major fatty acid components. On the basis of their phylogenetic, genomic and phenotypic properties, the five novel strains can be assigned to the genus Alcaligenes as a novel species, for which the name Alcaligenes aquatilis sp. nov. is proposed. The type strain is LMG 22996T (=CCUG 50924T).

Class 1 integrons and tetracycline resistance genes in alcaligenes, arthrobacter, and Pseudomonas spp. isolated from pigsties and manured soil

The presence of tetracycline resistance (Tc(r)) genes and class I integrons (in-1), and their ability to cotransfer were investigated in Tc(r) gram-negative (185 strains) and gram-positive (72 strains) bacteria from Danish farmland and pigsties. The isolates belonged to the groups or species Escherichia coli, Enterobacter spp., Arthrobacter spp., Alcaligenes spp., Pseudomonas spp., and Corynebacterium glutamicum. The 257 isolates were screened for in-1. Eighty-one of the gram-negative isolates were also screened for the Tc(r) genes tet(A), tet(B), and tet(C), and all (n = 72) gram-positive isolates were screened for tet(33). Fourteen (7%) of the soil isolates and eleven (25%) of the pigsty isolates contained in-1. All isolates that contained tet genes also contained in-1, except one gram-negative isolate from a pigsty that contained tet(B). All gram-positive isolates with in-1 also contained tet(33). No isolates contained more than one tet gene. The in-1-positive isolates were tested for resistance to selected antimicrobial agents and showed resistance to three to nine drugs. Filter-mating experiments showed cotransfer of Tc(r) and class I integrons from soil isolates to Escherichia coli and/or Pseudomonas putida. We conclude that soil bacteria in close contact to manure or pigsty environment may thus have an important role in horizontal spread of resistance. Use of tetracyclines in food animal production may increase not only Tc(r) but also multidrug resistance (caused by the presence tet genes and in-1) in bacteria.

Assessment of the microbial community in a constructed wetland that receives acid coal mine drainage

Constructed wetlands are used to treat acid drainage from surface or underground coal mines. However, little is known about the microbial communities in the receiving wetland cells. The purpose of this work was to characterize the microbial population present in a wetland that was receiving acid coal mine drainage (AMD). Samples were collected from the oxic sediment zone of a constructed wetland cell in southeastern Ohio that was treating acid drainage from an underground coal mine seep. Samples comprised Fe(III) precipitates and were pretreated with ammonium oxalate to remove interfering iron, and the DNA was extracted and purified by agarose gel electrophoresis prior to amplification of portions of the 16S rRNA gene. Amplified products were separated by denaturing gradient gel electrophoresis and DNA from seven distinct bands was excised from the gel and sequenced. The sequences were matched to sequences in the GenBank bacterial 16S rDNA database. The DNA in two of the bands yielded matches with Acidithiobacillus ferrooxidans and the DNA in each of the remaining five bands was consistent with one of the following microorganisms: Acidithiobacillus thiooxidans, strain TRA3-20 (a eubacterium), strain BEN-4 (an arsenite-oxidizing bacterium), an Alcaligenes sp., and a Bordetella sp. Low bacterial diversity in these samples reflects the highly inorganic nature of the oxic sediment layer where high abundance of iron- and sulfur-oxidizing bacteria would be expected. The results we obtained by molecular methods supported our findings, obtained using culture methods, that the dominant microbial species in an acid receiving, oxic wetland are A. thiooxidans and A. ferrooxidans.

[Isolation and characterization of a chlorpyrifos degrading bacteria and its bioremediation application in the soil]

A strain DSP3 capable of utilizing chlorpyrifos as the sole carbon and energy sources was isolated. Based on the results of phenotypic features, phylogenetic of 16S rDNA sequence, DNA (G + C) mol% and DNA homology between strain DSP3 and reference strains, the strain DSP3 is identified as Alcaligenes faecalis. The degradation rate of chlorpyrifos was at 98.6% (100 mg/L) in liquid culture medium within 18 days and nearly 100% (100 mg/kg) in soil within 20 days respectively. An addition of strain DSP3 (10(8) cells/g) to soil resulted in a higher degradation rate than noninoculated soils. The different degrading rate of chlorpyrifos in four types of treated soils suggests that the dissipation is mediated by the activity of the soil microorganisms.

Reclassification of Alcaligenes latus strains IAM 12599T and IAM 12664 and Pseudomonas saccharophila as Azohydromonas lata gen. nov., comb. nov., Azohydromonas australica sp. nov. and Pelomonas saccharophila gen. nov., comb. nov., respectively

The aim of this study was to clarify the taxonomic position of the nitrogen-fixing and hydrogen-oxidizing bacteria Alcaligenes latus strains IAM 12599T, IAM 12664 and IAM 12665 and Pseudomonas saccharophila IAM 14368T. It was found that the type strain of Alcaligenes latus, IAM 12599T, showed 99·9 and 96·1 % 16S rRNA gene sequence similarity to strains IAM 12665 and IAM 12664, respectively. A comparison using DNA–DNA hybridization suggested that strains IAM 12599T and IAM 12665 belong to a single species (89·7 %) and that strain IAM 12664 (35·1 %) forms a separate species. The phenotypic characteristics also support the conclusion that these bacteria should be identified as two species of a new genus: Azohydromonas lata gen. nov., comb. nov. (type strain IAM 12599T=DSM 1122T=LMG 3321T=ATCC 29712T; reference strain IAM 12665=DSM 1123=LMG 3325=ATCC 29714) and Azohydromonas australica sp. nov. (type strain IAM 12664T=DSM 1124T=LMG 3324T=ATCC 29713T). Pseudomonas saccharophila IAM 14368T was found to be closely related to the phototrophic bacterium Roseateles depolymerans, with 96·8 % 16S rRNA gene sequence similarity, but the two bacteria are quite different with respect to their metabolism and some significant phenotypic characteristics, suggesting that they cannot be included in a single genus. Further studies on their nifH gene sequences, G+C content of the DNA and cellular fatty acid composition confirm that Pseudomonas saccharophila should be reclassified: the name Pelomonas saccharophila gen. nov., comb. nov. is proposed, with the type strain IAM 14368T (=LMG 2256T=ATCC 15946T).

Spontaneous liberation of intracellular polyhydroxybutyrate granules in Escherichia coli

Despite receiving much attention as a biodegradable substitute for conventional non-biodegradable plastics, the commercial use of polyhydroxybutyrate (PHB) remains limited because of its high production cost. In order to reduce the recovery/purification cost, which forms over half of the total production cost, we have developed a new cultivation method which enables spontaneous liberation of PHB by modulation of the initial inoculum size and the medium composition in recombinant Escherichia coli harboring Alcaligenes eutrophus phbCAB genes. In flask cultivation using a low cell inoculum and 2x LB medium containing 21% glucose, autolysis of 80.2% as well as yields of 85.2 g/l of PHB and a PHB content of 99.0% (w/w) were obtained. The glucose conversion rate was 0.43. The strategies developed in this study can minimize complex and unfavorable efforts required for efficient recovery/purification processes, thereby enabling biodegradable plastic to be produced by the recombinant E. coli so as to compete with conventional non-biodegradable plastic.

Alcaligenes xylosoxidans bacteremia: clinical features and microbiological characteristics of isolates

Bacteremia caused by Alcaligenes xylosoxidans is rare. Between 1999 and 2002, 12 cases of bacteremia caused by A. xylosoxidans were diagnosed at a tertiary referral center in central Taiwan. The clinical features of these patients and the antimicrobial susceptibilities and pulsed-field gel electrophoresis (PFGE) pattern of their blood isolates were studied. All infections were acquired nosocomially. All of the adult patients had underlying diseases, and 10 (83%) had undergone an invasive procedure. The clinical syndrome included primary bacteremia in 7 patients (58%), and catheter-associated bacteremia, surgical wound infection, pneumonia, urinary tract infection, and empyema in 1 each. Polymicrobial bacteremia was found in 1 patient. The case-fatality rate was 17% (2/12). All isolates were susceptible to piperacillin and ceftazidime and resistant to aminoglycoside, ciprofloxacin and cefepime. Susceptibility to imipenem (67%), ampicillin-sulbactam (75%) and trimethoprim-sulfamethoxazole (92%) was variable. Genetic fingerprints obtained by PFGE showed identical pattern in the isolates from 2 neonates, indicating the epidemiologic relatedness of these infections. We conclude that A. xylosoxidans isolates are multi-resistant and A. xylosoxidans bacteremia should be considered as a possible etiology of infection after invasive procedures in patients with underlying diseases. Strict infection control is needed to prevent this infection.

Establishment of a genetically marked insect-derived symbiont in multiple host plants

Alcaligenes xylosoxidans subsp. denitrificans, originally isolated from the cibarial region of the foregut of the glassy-winged sharpshooter (Homalodisca coagulata), was transformed using the Himar1 transposition system to express EGFP. Seedlings of six potential host plants were inoculated with transformed bacteria and 2 weeks later samples were taken 5 cm away and analyzed by quantitative real-time PCR using primers designed to amplify the gene insert. The largest colony of 3,591,427 cells/2 cm of A. xylosoxidans subsp. denitrificans was found in Citrus limon, with almost all plants testing positive in both trials. The amount of colonization decreased in the other plants tested in the following order: orange (Citrus sinensis "sweet orange") > chrysanthemum (Chrysanthemum grandiflora cv. "White Diamond") > periwinkle (Vinca rosea) > crepe myrtle (Lagerstroemia indica) > grapevine (Vitis vinifera cv. Chardonnay). The bacterium's preference for citrus paralleled the host insect's preference for this same plant. Additional tests determined that A. xylosoxidans subsp. denitrificans thrives as a nonpathogenic, xylem-associated endophyte.

Heterologous metalloprotein biosynthesis in Escherichia coli: conditions for the overproduction of functional copper-containing nitrite reductase and azurin from Alcaligenes xylosoxidans

This paper reports on the optimization of conditions for the overproduction and isolation of two recombinant copper metalloproteins, originally encoded on the chromosome of the dentrifying soil bacterium Alcaligenes xylosoxidans, in the heterologous host Escherichia coli. The trimeric enzyme nitrite reductase (NiR) contains both type-1 and type-2 Cu centres, whilst its putative redox partner, azurin I, is monomeric and has only a type-1 Cu centre. Both proteins were processed and exported to the periplasm of E. coli, which is consistent with their periplasmic location in their native host A. xylosoxidans. NiR could be readily purified from the periplasmic fraction of E. coli but the enzyme as isolated possessed only type-1 Cu centres. The type-2 Cu centre could be fully reconstituted by incubation of the periplasmic fraction with copper sulfate prior to enzyme purification. Azurin I could only be isolated with a fully occupied type-1 centre when isolated from the crude cell extract but not after isolation from the periplasmic fraction, suggesting loss of the copper due to proteolysis. Based on a number of criteria, including spectroscopic, mass spectrometric, biochemical and structural analyses, both recombinant proteins were found to be indistinguishable from their native counterparts isolated from A. xylosoxidans. The findings of this work have important implications for the overproduction of recombinant metalloproteins in heterologous hosts.

Insights into Redox Partner Interactions and Substrate Binding in Nitrite Reductase from Alcaligenes xylosoxidans: Crystal Structures of the Trp138His and His313Gln Mutants,

Dissimilatory nitrite reductase catalyses the reduction of nitrite to nitric oxide within the key biological process of denitrification. We present biochemical and structural results on two key mutants, one postulated to be important for the interaction with the partner protein and the other for substrate entry. Trp138, adjacent to one of the type-1 Cu ligands, is one of the residues surrounding a small depression speculated to be important in complex formation with the physiological redox partners, azurin I and II. Our data reveal that the Trp138His mutant is fully active using methyl viologen as an artificial electron donor, but there is a large decrease in activity using azurin I. These observations together with its crystal structure at a high resolution of 1.6 A confirm the importance of Trp138 in electron transfer and thus in productive interaction with azurin. A "hydrophobic pocket" on the protein surface has been identified as the channel through which nitrite may be guided to the catalytic type-2 Cu site. Glu133 and His313 at the opening of the pocket are conserved among most blue and green copper nitrite reductases (CuNiRs). The failure to soak the substrate into our high-resolution crystal form of native and mutant CuNiRs has been linked to the observation of an extraneous poly(ethylene glycol) (PEG) molecule interacting with His313. We present the crystal structure of His313Gln and the substrate-bound mutant at high resolutions of 1.65 and 1.72 A, respectively. The observation of the substrate-bound structure for the His313Gln mutant and inhibitory studies with PEG establishes the role of the hydrophobic pocket as the port of substrate entry.

Site-directed mutagenesis alters DnaK-dependent folding process

The overproduction of d-aminoacylase (A6-d-ANase) of Alcaligenes xylosoxydans subsp. xylosoxydans A-6 (Alcaligenes A-6) is accompanied by aggregation of the overproduced protein, and its soluble expression is facilitated by the coexpression of DnaK-DnaJ-GrpE (DnaKJE). When the A6-d-ANase gene was expressed in the Escherichia coli dnaK mutant dnaK756, little activity was observed in the soluble fraction, and it was restored by the coexpression of DnaKJE or the substitution of the R354 residue of A6-d-ANase for lysine. These results suggest that the guanidino group of the R354 residue of A6-d-ANase disturbs its proper folding in the absence of DnaK and the disturbance is eliminated by binding of DnaK to the R354 residue in the presence of DnaK. This is the first report that the DnaK-dependent folding process of the enzyme is altered by site-directed mutagenesis.

Microdiversity of phenol hydroxylase genes among phenol-degrading isolates of Alcaligenes sp. from an activated sludge system

Enterobacterial repetitive intergenic consensus (ERIC)-PCR fingerprinting classified 97 phenol-degrading isolates with identical amplified ribosomal DNA restriction analysis (ARDRA) patterns into six genotypic groups. The 16S rRNA gene of the representative isolate of each group had higher than 99.47% common identity with each other and higher than 98% identity with the type strain of Alcaligenes faecalis. PCR-TGGE (temperature gradient gel electrophoresis) analysis of the genes of the largest subunit of the multi-component phenol hydroxylase (LmPH) in each isolate followed with sequencing showed that isolates within each ERIC-PCR group had identical LmPH gene sequences. Among the six different ERIC-PCR groups, two were found to harbor two different LmPH genes encoding low- and high-Ks (affinity constants) phenol hydroxylases, and the low-Ks type LmPH was identical in sequence with one predominant LmPH of the parental activated sludge. Three ERIC-PCR groups had only the high-Ks type and one had no sequence similar to the known LmPHs. Our work suggests that there is no correlation between the phylogenetic groupings of phenol-degrading bacteria and their LmPH genotypes possibly due to extensive horizontal gene transfer of this functional gene.

omega-Amino acid:pyruvate transaminase from Alcaligenes denitrificans Y2k-2: a new catalyst for kinetic resolution of beta-amino acids and amines

Alcaligenes denitrificans Y2k-2 was obtained by selective enrichment followed by screening from soil samples, which showed omega-amino acid:pyruvate transaminase activity, to kinetically resolve aliphatic beta-amino acid, and the corresponding structural gene (aptA) was cloned. The gene was functionally expressed in Escherichia coli BL21 by using an isopropyl-beta-D-thiogalactopyranoside (IPTG)-inducible pET expression system (9.6 U/mg), and the recombinant AptA was purified to show a specific activity of 77.2 U/mg for L-beta-amino-n-butyric acid (L-beta-ABA). The enzyme converts various beta-amino acids and amines to the corresponding beta-keto acids and ketones by using pyruvate as an amine acceptor. The apparent K(m) and V(max) for L-beta-ABA were 56 mM and 500 U/mg, respectively, in the presence of 10 mM pyruvate. In the presence of 10 mM L-beta-ABA, the apparent K(m) and V(max) for pyruvate were 11 mM and 370 U/mg, respectively. The enzyme exhibits high stereoselectivity (E > 80) in the kinetic resolution of 50 mM D,L-beta-ABA, producing optically pure D-beta-ABA (99% enantiomeric excess) with 53% conversion.

Identification, molecular biotyping and ultrastructural studies of bacterial communities isolated from two damaged frescoes of St Damian's Monastery in Assisi

AIM

To investigate the composition of the microbial community in biodeterioration of two frescoes in St Damian's Monastery in Assisi.

METHODS AND RESULTS

A total of 1292 colonies were isolated from the most deteriorated parts, analysed by microbiological, biomolecular and ultrastructural techniques, and taxonomically classified. Molecular biotyping of Staphylococcus cohnii colonies, one of the most prevalent bacterial species, showed a very restricted genome diversity while Bacillus licheniformis were very homogeneous by RFLP, tDNA-PCR and random-amplified polymorphic DNA. Electron microscopy confirmed heterogeneity of the bacterial population in the different sampling areas.

CONCLUSIONS

Several of the identified species are widespread in the soil or saprophytes of human skin. Although unable to demonstrate that they are involved in biodeterioration, they may represent trophic elements contributing to fungi-related chromatic alterations when adequate environmental conditions occur. Deterioration may in part be prevented or controlled by adequate air filtering or conditioning of the room.

Delivery of a Genetically Marked Alcaligenes sp. to the Glassy-Winged Sharpshooter for Use in a Paratransgenic Control Strategy

An artificial feeding system was designed for the glassy-winged sharpshooter (GWSS), Homalodisca coagulata Say (Hemiptera: Cicadellidae). The system, unlike previous systems, provided enough nutrients to GWSS to survive for 48 h. A system like this is a prerequisite to examining the potential use of paratransgenesis to interrupt transmission of Xylella fastidiosa, the bacterial pathogen causing Pierce's disease of grape, by insect vectors. We developed a system for short-term feeding of GWSS that allows for the introduction of bacteria in liquid medium, and we have demonstrated the ability of Alcaligenes xylosoxidans denitrificans, expressing a red fluorescent protein (dsRed), to colonize the cibarial region of the GWSS foregut for up to 5 weeks post-exposure. Alcaligenes xylosoxidans denitrificans thus occupies the same region in the foregut as the pathogen, Xylella fastidiosa.

In-situ characterization of microbial community in an A/O submerged membrane bioreactor with nitrogen removal

The bacterial community involved in removing nitrogen from sewage and their preferred DO environment within an anoxic/oxic membrane bioreactor (A/O MBR) was investigated. A continuously operated laboratory-scale A/O MBR was maintained for 360 d. At a sludge age of 150 d and a C/N ratio of 3.5, the system was capable of removing 88% of the influent nitrogen from raw wastewater through typical nitrogen removal transformations (i.e. aerobic ammonia oxidation and anoxic nitrate reduction). Characterization of the A/O MBR bacterial community was carried out using fluorescence in situ hybridization (FISH) techniques. FISH results further showed that Nitrosospira spp. and Nitrospira spp. were the predominant groups of ammonia and nitrite oxidizing group, respectively. They constituted up to 11% and 6% of eubacteria at DO below 0.05 mg/l (low DO), respectively, and about 14% and 9% of eubacteria at DO between 2-5 mg/l (sufficient DO), respectively, indicating preference of nitrifiers for a higher DO environment. Generally low counts of the genus Paracoccus were detected while negative results were observed for Paracoccus denitrificans, Alcaligenes spp, and Pseudomonas stutzeri under the low and sufficient DO environments. The overall results indicate that Nitrosospira spp., Nitrospira spp. and members of Paracoccus spp. can be metabolically functional in nitrogen removal in the laboratory-scale A/O MBR system.

In silico prediction and validation of the importance of the Entner-Doudoroff pathway in poly(3-hydroxybutyrate) production by metabolically engineered Escherichia coli

The metabolic network of Escherichia coli was constructed and was used to simulate the distribution of metabolic fluxes in wild-type E. coli and recombinant E. coli producing poly(3-hydroxybutyrate) [P(3HB)]. The flux of acetyl-CoA into the tricarboxylic acid (TCA) cycle, which competes with the P(3HB) biosynthesis pathway, decreased significantly during P(3HB) production. It was notable to find from in silico analysis that the Entner-Doudoroff (ED) pathway flux increased significantly under P(3HB)-accumulating conditions. To prove the role of ED pathway on P(3HB) production, a mutant E. coli strain, KEDA, which is defective in the activity of 2-keto-3-deoxy-6-phosphogluconate aldolase (Eda), was examined as a host strain for the production of P(3HB) by transforming it with pJC4, a plasmid containing the Alcaligenes latus P(3HB) biosynthesis operon. The P(3HB) content obtained with KEDA (pJC4) was lower than that obtained with its parent strain KS272 (pJC4). The reduced P(3HB) biosynthetic capacity of KEDA (pJC4) could be restored by the co-expression of the E. coli eda gene, which proves the important role of ED pathway on P(3HB) synthesis in recombinant E. coli as predicted by metabolic flux analysis.

[Phenotypic and genotypic characteristics of non fermenting atypical strains recovered from cystic fibrosis patients]

We used partial 16S rRNA gene (16S DNA) sequencing for the prospective identification of nonfermenting Gram-negative bacilli recovered from patients attending our cystic fibrosis center (hôpital Necker-Enfants malades), which gave problematic results with conventional phenotypic tests. During 1999, we recovered 1093 isolates of nonfermenting Gram-negative bacilli from 702 sputum sampled from 148 patients. Forty-six of these isolates (27 patients) were not identified satisfactorily in routine laboratory tests. These isolates were identified by 16S DNA sequencing as Pseudomonas aeruginosa (19 isolates, 12 patients), Achromobacter xylosoxidans (10 isolates, 8 patients), Stenotrophomonas maltophilia (9 isolates, 9 patients), Burkholderia cepacia genomovar I/III (3 isolates, 3 patients), Burkholderia vietnamiensis (1 isolate), Burkholderia gladioli (1 isolate) and Ralstonia mannitolilytica (3 isolates, 2 patients). Fifteen isolates (33%) were resistant to all antibiotics in routine testing. Sixteen isolates (39%) resistant to colistin were recovered on B. cepacia-selective medium: 2 P. aeruginosa, 3 A. xylosoxidans, 3 S. maltophilia and the 8 Burkholderia--Ralstonia isolates. The API 20NE system gave no identification for 35 isolates and misidentified 11 isolates (2 P. aeruginosa, 2 A. xylosoxidans and 1 S. maltophilia classified as B. cepacia ). Control measures and/or treatment were clearly improved as a result of 16S DNA sequencing in three of these cases. This study confirms the weakness of phenotypic methods for identification of atypical nonfermenting Gram-negative bacilli recovered from cystic fibrosis patients. The genotypic methods, such as 16S DNA sequencing which allows identification of strains in routine practice, appears to have a small, but significant impact on the clinical management of CF patients.

Long-term analysis of diesel fuel consumption in a co-culture of Acinetobacter venetianus, Pseudomonas putida and Alcaligenes faecalis

The dynamics of a microbial population isolated from superficial waters of Venice Lagoon and the ability to utilise diesel fuel (n-alkanes mixture C12-C28) as the sole carbon and energy source were studied in a long-term reconstruction experiment. The reconstructed microbial population consisted of three bacterial strains belonging to the species Acinetobacter venetianus, Pseudomonas putida, and Alcaligenes faecalis, which were able to oxidise n-alkanes to alkanoates, n-alkanols to alkanoates, or only n-alkanoates, respectively. Three different approaches: plate counting, cell counting by epifluorescence microscopy with DAPI staining, and by fluorescence in situ hybridisation (FISH) by using a probe conjugate with fluoresceine isothiocyanate specifically targeted towards the 16S rRNA of bacteria belonging to the genus Acinetobacter were used to monitor the growth of the bacterial population. The growth of A. venetianus was stimulated by the presence of other strains, suggesting a beneficial interaction. After the first week of growth A. venetianus cells formed aggregates, as confirmed by confocal microscopy (CLSM), which allowed them to be distinguished from free cells. A relationship between cell number and measured areas (microm2) per aggregate was found. Each cell presented an average surface of 1.21 microm2. Each aggregate was formed by a cellular monolayer biofilm consisting of up to several thousands of cells. The A. venetianus aggregates increased in number and size over time, but after two weeks fragmentation events, which had a beneficial effect on the growth of P. putida and A. faecalis, occurred.

Introduction of a pi-pi interaction at the active site of a cupredoxin: characterization of the Met16Phe Pseudoazurin mutant

The Met16Phe mutant of the type 1 copper protein pseudoazurin (PACu), in which a phenyl ring is introduced close to the imidazole moiety of the His81 ligand, has been characterized. NMR studies indicate that the introduced phenyl ring is parallel to the imidazole group of His81. The mutation has a subtle effect on the position of the two S(Cys)-->Cu(II) ligand-to-metal charge transfer bands in the visible spectrum of PACu(II) and a more significant influence on their intensities resulting in a A(459)/A(598) ratio of 0.31 for Met16Phe as compared to a A(453)/A(594) ratio of 0.43 for wild-type PACu(II) at pH 8. The electron paramagnetic resonance spectrum of the Met16Phe variant is more axial than that of the wild-type protein, and the resonance Raman spectrum of the mutant exhibits subtle differences. A C(gamma)H proton of Met86 exhibits a much smaller hyperfine shift in the paramagnetic (1)H NMR spectrum of Met16Phe PACu(II) as compared to its position in the wild-type protein, which indicates a weaker axial Cu-S(Met86) interaction in the mutant. The Met16Phe mutation results in an approximately 60 mV increase in the reduction potential of PACu. The pK(a) value of the ligand His81 decreases from 4.9 in wild-type PACu(I) to 4.5 in Met16Phe PACu(I) indicating that the pi-pi contact with Phe16 stabilizes the Cu-N(His81) interaction. The Met16Phe variant of PACu has a self-exchange rate constant at pH 7.6 (25 degrees C) of 9.8 x 10(3) M(-)(1) s(-)(1) as compared to the considerably smaller value of 3.7 x 10(3) M(-)(1) s(-)(1) for the wild-type protein under identical conditions. The enhanced electron transfer reactivity of Met16Phe PACu is a consequence of a lower reorganization energy due to additional active site rigidity caused by the pi-pi interaction between His81 and the introduced phenyl ring.