Structures of homologous composite transposons carrying cbaABC genes from Europe and North America

IS1071 is a class II transposable element carrying a tnpA gene related to the transposase genes of the Tn3 family. Copies of IS1071 that are conserved with more than 99% nucleotide sequence identity have been found as direct repeats flanking a remarkable variety of catabolic gene sequences worldwide. The sequences of chlorobenzoate catabolic transposons found on pBRC60 (Tn5271) in Niagara Falls, N.Y., and on pCPE3 in Bologna, Italy, show that these transposons were formed from highly homologous IS1071 and cbaABC components (levels of identity, > 99.5 and > 99.3%, respectively). Nevertheless, the junction sequences between the IS1071L and IS1071R elements and the internal DNA differ by 41 and 927 bp, respectively, suggesting that these transposons were assembled independently on the two plasmids. The formation of the right junction in both transposons truncated an open reading frame for a putative aryl-coenzyme A ligase with sequence similarity to benzoate- and p-hydroxybenzoate-coenzyme A ligases of Rhodopseudomonas palustris.

Effect of vitamins on the aerobic degradation of 2-chlorophenol, 4-chlorophenol, and 4-chlorobiphenyl

The effect of vitamins on the aerobic degradation and dechlorination of 2-chlorophenol and 4-chlorophenol by Pseudomonas pickettii, strain LD1, and 4-chlorobiphenyl by Pseudomonas sp. strain CPE1 was determined. These microorganisms are capable of using the target compounds as the sole carbon and energy source, but do not need vitamins to metabolize them. The addition to the culture medium of a vitamin solution containing biotin, folic acid, pyridoxine hydrochloride, riboflavin, thiamine hydrochloride, niacin, pantothenic acid, cyanocobalamin, p-aminobenzoic acid, and thioctic acid (total final concentration: < or = 600 ppb) resulted in a 7%-16% increase in the amount of target compounds degraded over the incubation period required for the concentration of the compound in the cultures to drop to approximately zero. A corresponding increase in the amount of chloride ion produced was also detected during the same period, indicating active (and often stoichiometric) dechlorination of the target compounds.

Aerobic dechlorination of low-chlorinated biphenyls by bacterial biofilms in packed-bed batch bioreactors

Cells of an aerobic three-membered bacterial co-culture, designated as ECO3, capable of cometabolizing and aerobically dechlorinating low-chlorinated biphenyls in the presence of biphenyl, were immobilized on Manville silica beads, on frosted-glass beads and on polyurethane foam cubes in packed-bed bioreactors continuously fed with a biphenyl-saturated air stream. The ECO3 biofilm reactors were found to be capable of extensively mineralizing several pure dichlorobiphenyls (75 mg/l) and Aroclor 1221 (75 mg/l) in batch mode. Immobilized ECO3 cells could aerobically degrade and dechlorinate the dichlorobiphenyls tested more extensively than suspended ECO3 cells. Among the three biofilm reactors, the glass bead bioreactor and the polyurethane bioreactor exhibited the highest capability of mineralizing both dichlorobiphenyls and Aroclor 1221; the polychlorinated biphenyl availability in the bioreactors more than the biomass availability, both depending on the nature of the support employed, significantly governed the efficiency of the treatment. These results are of interest for the possible development of a bioreactor system for continuous treatment of polychlorinated-biphenyl-contaminated wastewaters.

2-Chlorobenzoic acid and 2,5-dichlorobenzoic acid metabolism by crude extracts of Pseudomonas sp. CPE2 strain

Crude extracts of Pseudomonas sp. CPE2 strain, which is capable of growing on 2-chlorobenzoic acid (2-CBA) and 2,5-dichlorobenzoic acid (2,5-dCBA) in the absence of other carbon sources, were found to be capable of bioconverting 2-CBA and 2,5-dCBA to catechol and 4-chlorocatechol, respectively, by a reaction requiring molecular oxygen and exogenous NADH. Extracts obtained from 2-CBA-grown cells in the presence of 2-CBA and from 2,5-dCBA-grown cells in the presence of 2,5-dCBA were found to have activities similarly influenced by the assay parameters pH, temperature, and by concentration of oxygen, protein, Fe2+, FAD and NADH in the assay medium. In addition, the activity of the two crude extracts in the presence of 2-CBA or 2,5-dCBA was described by very similar Michaelis-Menten kinetic parameters. These observations led to the speculation that a unique broad-spectrum chlorobenzoate 1,2-dioxygenase catalyses the 2-CBA and 2,5-dCBA metabolism both in 2-CBA- and 2,5-dCBA-grown CPE2 cells.

Aroclor 1221 aerobic dechlorination by a bacterial co-culture: role of chlorobenzoic acid degrading bacteria in the process

A bacterial co-culture, ECO3, constituted by a polychlorobiphenyl degrading bacterium, Pseudomonas sp. strain CPE1, and two chlorobenzoic acid degrading bacteria, could grow on Aroclor 1221 (75 mg/L) as the sole carbon source without accumulating chlorinated aromatic metabolites in the medium; 44.5% of the Aroclor 1221 organic chlorine was detected as chloride ion in the medium after 115 h of incubation in batch condition. When glass beads (diameter = 3 mm, 30% w/v) or Triton X-100 (0.066% v/v) were added to ECO3 cultures, average dechlorination percentages were 80% and 89.5%, respectively, after the same incubation time. These percentages were significantly higher than those previously observed with the only polychlorobiphenyl degrading member of ECO3, CPE1 strain, in the same culture conditions. This result can be ascribed to the capability of the ECO3 chlorobenzoic acid degrading bacteria of completely mineralizing the chlorinated benzoic acids produced during the Aroclor 1221 degradation. The depletion of these intermediates seems to prevent toxic or inhibitory effects on the bacteria thus permitting a larger Aroclor 1221 metabolization.

The presence of glass beads or Triton X-100 in the medium enhances the aerobic dechlorination of Aroclor 1221 in Pseudomonas sp. CPE1 culture

The culture pure Pseudomonas sp. CPE1 strain capable of metabolizing low-chlorinated biphenyls in the presence of biphenyl was found to be able to grow on Aroclor 1221 in the absence of an additional carbon source. The presence of glass beads (diameter = 3 mm, 30% w/v) or Triton X-100 (0.066% v/v) in the culture medium significantly enhanced the aerobic dechlorination of the polychlorinated biphenyls present in Aroclor 1221 in batch cultures of CPE1 strain. This result has been ascribed to an increase of Aroclor 1221 bioavailability in the cultures containing glass beads or Triton X-100, probably deriving from a greater interface area PCB-water, i.e. the surface area on which the polychlorobiphenyl degradation seems to take place.

Aerobic degradation and dechlorination of 2-chlorophenol, 3-chlorophenol and 4-chlorophenol by a Pseudomonas pickettii strain

A Gram-negative aerobic bacterium capable of using 2-chlorophenol (2-CP), 3-chlorophenol (3-CP) and 4-chlorophenol (4-CP) as sole carbon sources was isolated and characterized. The bacterium, designated LD1, was identified to be a Pseudomonas pickettii strain. LD1 was able to totally degrade and dechlorinate 2-CP (initial concentration: 1.51 mmol l-1), 3-CP (initial concentration: 0.57 mmol l-1) and 4-CP (initial concentration: 0.75 mmol l-1) within 30, 30 and 40 h of incubation, respectively, under growing-cell batch conditions. LD1 was also found to be able to metabolize chlorocatechols in growing- and resting-cell conditions. This suggests that the bacterium degrades monochlorophenols through a chlorocatechol pathway. In addition, LD1 was found to be capable of readily metabolizing other organic compounds such as phenol, benzoic acid, hydroxybenzoic acids and hydroquinone. Because of the broad spectrum of monochlorophenols and organic compounds that LD1 can degrade, this bacterium appears to have the potential for being successfully used in the biotreatment of wastewaters and in soil decontamination.

Influence of organic and inorganic growth supplements on the aerobic biodegradation of chlorobenzoic acids

The effect of yeast extract and its less complex substituents on the rate of aerobic dechlorination of 2-chlorobenzoic acid (2-ClBZOH) and 2,5-dichlorobenzoic acid (2,5-Cl2BZOH) by Pseudomonas sp. CPE2 strain, and of 3-chlorobenzoic acid (3-ClBZOH), 4-chlorobenzoic acid (4-ClBZOH) and 3,4-dichlorobenzoic acid (3,4-Cl2BZOH) by Alcaligenes sp. CPE3 strain were investigated. Yeast extract at 50 mg/l increased the average dechlorination rate of 200 mg/l of 4-ClBZOH, 2,5-Cl2BZOH, 3,4-Cl2BZOH, 3-ClBZOH and 2-ClBZOH by about 75%, 70%, 55%, 7%, and 1%, respectively. However, in the presence of yeast extract the specific dechlorination activity of CPE2 and CPE3 cells (per unit biomass) was always lower than without yeast extract, although it increased significantly during the exponential growth phase. When a mixed vitamin solution or a mixed trace element solution was used instead of yeast extract the rate of 4-ClBZOH dechlorination increased by 30%-35%, whereas the rate of 2,5-Cl2BZOH and 3,4-Cl2BZOH dechlorination increased by only 2%-10%. The presence of vitamins or trace elements also resulted in a specific dechlorination activity that was generally higher than that observed for the same cells grown solely on chlorobenzoic acid. The results of this work indicate that yeast extract, a complex mixture of readily oxidizable carbon sources, vitamins, and trace elements, enhances the growth and the dechlorination activity of CPE2 and CPE3 cells, thus resulting in an overall increase in the rate of chlorobenzoic acid utilization and dechlorination.

[Gallbladder carcinoma. Our experience]

Carcinoma of the gallbladder is the most frequent neoplasm of the biliary tract. During the period between 1 January 1979 and 31 December 1991 a total of 1016 operations for cholecystectomy were performed by our Division of Surgery and 27 cases of gallbladder carcinoma were diagnosed. The symptoms were generally similar to those of benign hepatobiliary disorders. The diagnostic tests carried out did not allow a preoperative diagnosis of gallbladder carcinoma to be made. In the majority of cases diagnosis was a surprise following the histological analysis of the operated part. The prime therapy for these lesions is surgery. Since it is not possible to make an early diagnosis of this type of neoplasm, which in the majority of cases has a fatal prognosis, the authors consider that the finding of inveterate calculosis, large calculi and echographic thickening of the gallbladder wall represent indications for surgery even in the absence of major symptoms.

An attempt to control the polychlorocatechol pigment production during 3-chlorobenzoate aerobic co-metabolism in growing-cell batch culture

A strain of Pseudomonas fluorescens, designed CP30, was capable of co-metabolizing 3-chlorobenzoic acid via chlorocatechols, thus producing a polychlorocatechol black pigment. The pigment production was found to be enzyme-mediated in P. fluorescens cultures; however, the results of the autoxidation studies suggested that a large amount of pigment could derive from the simple autoxidation of the chlorocatechols accumulated in the CP30 culture during the 3-chlorobenzoate degradation. The polymerization of chlorocatechols should reduce the toxicity of the culture and generally resulted in a large production of a water-insoluble (i.e. a easily removable) pigment with the release a large amount of chloride ions. Both 3-chlorobenzoate degradation and pigment production were stimulated and inhibited in the same way by high and low pH values, respectively, in CP30 cultures; the culture conditions which permitted an extensive 3-chlorobenzoate degradation with the lowest pigment production were not identified. However, on the basis of the detoxification property of the pigment production process, high pH and dissolved oxygen concentrations appears to be the most suitable culture conditions for an enhanced detoxicant treatment of 3-clorobenzoate-contaminated waste water.

Regulation of dihydrodipicolinate synthase and diaminopimelate decarboxylase activity in Bacillus stearothermophilus

The feedback inhibition of the enzymes dihydrodipicolinate (DHDPS) and diaminopimelate decarboxylase (DAPD) in the wild strain Zu 183 of Bacillus stearothermophilus and in its S-(2-aminoethyl)-cysteine resistant L-lysine overproducing strain AEC 12 was studied. The optimum temperature and pH of both enzymes were also evaluated. No inhibition of DHDPS by L-lysine, L-threonine, L-methionine and L-isoleucine was observed either in the wild strain or in the AEC 12 mutant. DAPD was completely inhibited by L-lysine and only partially by L-threonine and L-methionine in Zu 183 and AEC 12 strains, but the concentration required was found to be much higher in the AEC 12 strain. The regulation mechanism of L-lysine biosynthesis in Bacillus stearothermophilus Zu 183 was also discussed.

Antibacterial effectiveness of dentin bonding systems

This study examined the antibacterial activities of several commercially available glass ionomer cements, dentin bonding systems and luting agents by employing both agar plate diffusion (APD) and growth inhibition (GI) methods. Amalgam and resin composites were also tested as control materials. In both methods (APD and GI), cylindrical specimens were used. Four bacteria strains were tested: Streptococcus mutans, S. salivarius, S. mitis and S. sanguis. These studies were performed using standardized innoculums with selective media, and the assayed materials were directly applied on the assay cultures and plates. The results of agar plate assay were in accordance with the results of growth inhibition method. The glass ionomer cements showed marked antibacterial activity. On the contrary, amalgam, composites, luting agents and dentinal bonding systems did not affect bacterial growth. The sensitivity of the growth method showed that all the strains were inhibited in the same way by each inhibitory material. The data suggest that the use of glass ionomer cements as cavity liners/bases may reduce the consequences of microleakage due to its antibacterial properties.

Biosynthesis and cytoplasmic accumulation of a chlorinated catechol pigment during 3-chlorobenzoate aerobic co-metabolism in Pseudomonas fluorescens

A strain of Pseudomonas fluorescens was capable of co-metabolizing 3-chlorobenzoic acid with the production of a chlorinated catechol black pigment. A peroxidase and another enzymatic activity referred to as a polyphenol oxidase were found to be involved in the oxidation of 4-chlorocatechol to 4-chloro-1,2-benzoquinone, i.e. in the production of highly reactive substrates for pigment formation. Therefore, P. fluorescens cells were seen to take an active part not only in 3-chlorobenzoate mineralization but also in overall pigment production. pH was found to be a key parameter in the regulation of the activity of P. fluorescens oxidoreductive enzymes. Ultrastructural investigations showed that electron dense granules of pigment were distributed throughout the cytoplasm of Pseudomonas fluorescens cells grown in presence of 3-chlorobenzoate, as confirmed also by Thiéry cytochemical investigations. In these cells, an extensive contraction of the cytoplasm as well as a significant damage to the cell wall after two days of incubation, suggested that pigment production caused a premature death of the cells accompanied by the leakage of the cell content. Pigment production seemed to occur mostly in the cytoplasmic context where the electron dense material accumulates until it is released in the medium after the cell lysis.

Effects of dentin surface treatments on the shear bond strength of Vitrabond

The influences of nine dentin surface treatments were evaluated on the shear bond strength of a new light-cured glass-ionomer cement (GIC) and on the SEM morphology of the treated dentin surfaces. The following treatments were performed: saline solution (control), NaOCl, acidic glycine, EDTA, malic acid, malic acid plus glycine, polyacrylic acid, tannic acid, and neutral+acidic oxalate solutions. Buccal dentin surfaces were polished with #320-grit abrasive paper, treated with one of the chemicals, washed, and air-dried. Cylindrical GIC samples were then applied to the dentin surface, stored in 100% humidity, and tested after 24 h. SEM observations demonstrated no effect of saline or NaOCl treatment on the smear layer but its complete removal with exposure of collagen fibrils after malic or malic acid plus glycine treatment. Partial removal of the smear layer occurred following glycine treatment and with tannic or polyacrylic acids. Complete removal of the smear layer was seen after EDTA or pyruvic acid treatment. Oxalate treatment produced a layer of crystals, which completely covered the dentin surface. Shear bond strength of GIC was significantly increased only by treatment with the oxalate solutions.

Degradation and mineralization of 3-chlorobiphenyl by a mixed aerobic bacterial culture

A mixed bacterial culture obtained from polychlorinated-biphenyl-contaminated river sediments proved capable of degrading 3-chlorobiphenyl (3-CB) under aerobic laboratory conditions. Almost total mineralization of 150 mg/l of 3-CB occurred when, after 3 days of incubation, the mineral medium was supplied with benzoic acid as a carbon source. Two strains of Pseudomonas capable of degrading the substrate to 3-chlorobenzoic acid and a strain of Pseudomonas fluorescens capable of co-metabolizing this metabolite were selected from the mixed culture. A nearly stoichiometric amount of chloride, which defines the percentage of total mineralization, was eliminated during mixed culture growth.

[Glass ionomer cements and dentinal pretreatments: the evaluation of their adhesion to the dentin]

The aim of the present study was to evaluate the shear bond strength test of two glass-ionomer cements (G C cement and Ketac Bond) after different chemical pretreatments of dentine surface. The following dentine pretreatments were used: sodium hypochlorite, polyacrylic acid, tannic acid, H3PO4, FeCl3, Fe ossalate, Tubulicid, H2O2 and aqueous solution as control. Flat dentine surface of human extracted teeth was treated with the chemical agents, washed and dried. Cylindrical specimens of glass-ionomer cement were applied on dentine surface. After 24 hours in humidifier the specimens were tested in a universal testing machine. A significant higher bond was obtained only from polyacrylic acid and sodium hypochlorite treatments. The present results suggest that dentine pretreatment represent an essential step in composite resin/glass-ionomer cement restorations.