Physical and biological parameters that determine the fate of p-chlorophenol in laboratory test systems.

Shake-flask and microcosm studies were conducted to determine the fate of para-chlorophenol (p-CP) in water and sediment systems and the role of sediment and nonsediment surfaces in the biodegradation process. Biodegradation of p-CP in estuarine water samples in shake flasks was slow over incubation periods of 300 h. The addition of detrital sediment resulted in immediate and rapid degradation evidenced by the production of 14CO2 from [14C]p-CP. The addition of sterile sediment, glass beads, or sand resulted in approximately four to six times more CO2 evolution than observed in the water alone. Densities of p-CP-degrading bacteria associated with the detrital sediment were 100 times greater than those enumerated in water. Bacteria in the water and associated with the sediment after preexposure of both water and sediment of p-CP demonstrated enhanced biodegradation. In some microcosms, p-CP was degraded completely in the top 1.0 cm of intact sediment beds. Sediment reworking activities by benthic invertebrates from one site were sufficient to mix p-CP deep into the sediment bed faster than biodegradation or molecular diffusion. p-CP was persistent at lower depths of the sediment, possibly a result of reduced oxygen conditions preventing aerobic biodegradation.     

Monohydroxylation of phenol and 2,5-dichlorophenol by toluene dioxygenase in Pseudomonas putida F1.

Pseudomonas putida F1 contains a multicomponent enzyme system, toluene dioxygenase, that converts toluene and a variety of substituted benzenes to cis-dihydrodiols by the addition of one molecule of molecular oxygen. Toluene-grown cells of P. putida F1 also catalyze the monohydroxylation of phenols to the corresponding catechols by an unknown mechanism. Respirometric studies with washed cells revealed similar enzyme induction patterns in cells grown on toluene or phenol. Induction of toluene dioxygenase and subsequent enzymes for catechol oxidation allowed growth on phenol. Tests with specific mutants of P. putida F1 indicated that the ability to hydroxylate phenols was only expressed in cells that contained an active toluene dioxygenase enzyme system. 18O2 experiments indicated that the overall reaction involved the incorporation of only one atom of oxygen in the catechol, which suggests either a monooxygenase mechanism or a dioxygenase reaction with subsequent specific elimination of water.     

Kinetic evidence for differential agonist and antagonist binding to bovine hippocampal synaptic membrane opioid receptors

To examine the kinetics of opioid receptor binding, the agonists [D-Ala2-D-Leu5]enkephalin (DADL) and [D-Ala2-MePhe4-Gly-ol5]enkephalin (DAGO) and the antagonists diprenorphine and naltrexone were used with bovine hippocampal synaptic plasma membranes. By computer modeling of equilibrium binding displacement curves utilizing the LIGAND program, we found opioid peptides bind with high affinity to single populations of synaptic plasma membranes receptors, whereas opiate alkaloids bind to multiple sites. Initial kinetic experiments revealed that agonist rates of association were radioligand concentration-independent. Pseudo first-order rate constants for DADL, DAGO, diprenorphine, and naltrexone association were estimated to be 5.63 X 10(5), 5.08 X 10(5), 4.60 X 10(6), and 2.3 X 10(6) mol-1 X s-1, respectively. After preincubation of 0.2-1 nM radioligand for variable time intervals, dissociation was initiated by addition of 1 microM unlabeled ligand. If saturation binding was achieved before dissociation was initiated, then nearly monophasic dissociation of DADL, DAGO, and diprenorphine and a biphasic off-rate for naltrexone were observed. When association times were reduced to pre-equilibrium intervals, the kinetics of dissociation of agonists became biphasic and association time-dependent, but that for antagonists did not change significantly. Comparisons by both graphical methods and computerized nonlinear regression analyses of rate constants revealed that the fraction of the rapid component of agonist dissociation decreases and that of the slow component is elevated with increasing receptor occupancy. In the presence of 100 mM NaCl, DADL dissociation became association time-independent. These data are consistent with the idea that the Na+ effect is brought about by a change of receptor to an antagonist-like conformation. On the basis of both association and dissociation kinetic data, opioid agonists appear to interact in a multistep process in which a rapid, reversible association is followed by the formation of a more tightly bound complex.     

Adaptation of Natural Microbial Communities to Degradation of Xenobiotic Compounds: Effects of Concentration, Exposure Time, Inoculum, and Chemical Structure

Adaptation of microbial communities to faster degradation of xenobiotic compounds after exposure to the compound was studied in ecocores. Radiolabeled test compounds were added to cores that contained natural water and sediment. Adaptation was detected by comparing mineralization rates or disappearance of a parent compound in preexposed and unexposed cores. Microbial communities in preexposed cores from a number of freshwater sampling sites adapted to degrade p-nitrophenol faster; communities from estuarine or marine sites did not show any increase in rates of degradation as a result of preexposure. Adaptation was maximal after 2 weeks and was not detectable after 6 weeks. A threshold concentration of 10 ppb (10 ng/ml) was observed; below this concentration no adaptation was detected. With concentrations of 20 to 100 ppb (20 to 100 ng/ml), the biodegradation rates in preexposed cores were much higher than the rates in control cores and were proportional to the concentration of the test compound. In addition, trifluralin, 2,4-dichlorophenoxyacetic acid, and p-cresol were tested to determine whether preexposure affected subsequent biodegradation. Microbial communities did not adapt to trifluralin. Adaptation to 2,4-dichlorophenoxyacetic acid was similar to adaptation to nitrophenol. p-Cresol was mineralized rapidly in both preexposed and unexposed communities.     

Production of 6-Phenylacetylene Picolinic Acid from Diphenylacetylene by a Toluene-Degrading Acinetobacter Strain

Several strategies for using enzymes to catalyze reactions leading to the synthesis of relatively simple substituted picolinic acids have been described. The goal of the work described here was to synthesize a more complex molecule, 6-phenylacetylene picolinic acid [6-(2-phenylethynyl)pyridine-2-carboxylic acid], for use as a potential endcapping agent for aerospace polymers. We screened 139 toluene-degrading strains that use a variety of catabolic pathways for the ability to catalyze oxidative transformation of diphenylacetylene. Acinetobacter sp. strain F4 catalyzed the overall conversion of diphenylacetylene to a yellow metabolite, which was identified as a putative meta ring fission product (2-hydroxy-8-phenyl-6-oxoocta-2,4-dien-7-ynoic acid [RFP]). The activity could be sustained by addition of toluene at a flow rate determined empirically so that the transformations were sustained in spite of the fact that toluene is a competitive inhibitor of the enzymes. The overall rate of transformation was limited by the instability of RFP. The RFP was chemically converted to 6-phenylacetylene picolinic acid by treatment with ammonium hydroxide. The results show the potential for using the normal growth substrate to provide energy and to maintain induction of the enzymes involved in biotransformation during preliminary stages of biocatalyst development.     

Purification and characterization of nitrobenzene nitroreductase from Pseudomonas pseudoalcaligenes JS45.

Pseudomonas pseudoalcaligenes JS45 grows on nitrobenzene as a sole source of carbon, nitrogen, and energy. The catabolic pathway involves reduction to hydroxylaminobenzene followed by rearrangement to o-amino-phenol and ring fission (S. F. Nishino and J. C. Spain, Appl. Environ. Microbiol. 59:2520, 1993). A nitrobenzene-inducible, oxygen-insensitive nitroreductase was purified from extracts of JS45 by ammonium sulfate precipitation followed by anion-exchange and gel filtration chromatography. A single 33-kDa polypeptide was detected by denaturing gel electrophoresis. The size of the native protein was estimated to be 30 kDa by gel filtration. The enzyme is a flavoprotein with a tightly bound flavin mononucleotide cofactor in a ratio of 2 mol of flavin per mol of protein. The Km for nitrobenzene is 5 microM at an initial NADPH concentration of 0.5 mM. The Km for NADPH at an initial nitrobenzene concentration of 0.1 mM is 183 microM. Nitrosobenzene was not detected as an intermediate of nitrobenzene reduction, but nitrosobenzene is a substrate for the enzyme, and the specific activity for nitrosobenzene is higher than that for nitrobenzene. These results suggest that nitrosobenzene is formed but is immediately reduced to hydroxylaminobenzene. Hydroxylaminobenzene was the only product detected after incubation of the purified enzyme with nitrobenzene and NADPH. Hydroxylaminobenzene does not serve as a substrate for further reduction by this enzyme. The products and intermediates are consistent with two two-electron reductions of the parent compound. Furthermore, the low Km and the inducible control of enzyme synthesis suggest that nitrobenzene is the physiological substrate for this enzyme.     

Pathway for Biodegradation of p-Nitrophenol in a Moraxella sp

A Moraxella strain grew on p-nitrophenol with stoichiometric release of nitrite. During induction of the enzymes for growth on p-nitrophenol, traces of hydroquinone accumulated in the medium. In the presence of 2,2′-dipyridyl, p-nitrophenol was converted stoichiometrically to hydroquinone. Particulate enzymes catalyzed the conversion of p-nitrophenol to hydroquinone in the presence of NADPH and oxygen. Soluble enzymes catalyzed the conversion of hydroquinone to γ-hydroxymuconic semialdehyde, which was identified by high-performance liquid chromatography (HPLC)-mass spectroscopy. Upon addition of catalytic amounts of NAD⁺, γ-hydroxymuconic semialdehyde was converted to β-ketoadipic acid. In the presence of pyruvate and lactic dehydrogenase, substrate amounts of NAD were required and γ-hydroxymuconic semialdehyde was converted to maleylacetic acid, which was identified by HPLC-mass spectroscopy. Similar results were obtained when the reaction was carried out in the presence of potassium ferricyanide. Extracts prepared from p-nitrophenol-growth cells also contained an enzyme that catalyzed the oxidation of 1,2,4-benzenetriol to maleylacetic acid. The enzyme responsible for the oxidation of 1,2,4-benzenetriol was separated from the enzyme responsible for hydroquinone oxidation by DEAE-cellulose chromatography. The results indicate that the pathway for biodegradation of p-nitrophenol involves the initial removal of the nitro group as nitrite and formation of hydroquinone. 1,4-Benzoquinone, a likely intermediate in the initial reaction, was not detected. Hydroquinone is converted to β-ketoadipic acid via γ-hydroxymuconic semialdehyde and maleylacetic acid.     

Biotransformation of nitrobenzene by bacteria containing toluene degradative pathways.

Nonpolar nitroaromatic compounds have been considered resistant to attack by oxygenases because of the electron withdrawing properties of the nitro group. We have investigated the ability of seven bacterial strains containing toluene degradative pathways to oxidize nitrobenzene. Cultures were induced with toluene vapor prior to incubation with nitrobenzene, and products were identified by high-performance liquid chromatography and gas chromatography-mass spectrometry. Pseudomonas cepacia G4 and a strain of Pseudomonas harboring the TOL plasmid (pTN2) did not transform nitrobenzene. Cells of Pseudomonas putida F1 and Pseudomonas sp. strain JS150 converted nitrobenzene to 3-nitrocatechol. Transformation of nitrobenzene in the presence of 18O2 indicated that the reaction in JS150 involved the incorporation of both atoms of oxygen in the 3-nitrocatechol, which suggests a dioxygenase mechanism. P. putida 39/D, a mutant strain of P. putida F1, converted nitrobenzene to a compound tentatively identified as cis-1,2-dihydroxy-3-nitrocyclohexa-3,5-diene. This compound was rapidly converted to 3-nitrocatechol by cells of strain JS150. Cultures of Pseudomonas mendocina KR-1 converted nitrobenzene to a mixture of 3- and 4-nitrophenol (10 and 63%, respectively). Pseudomonas pickettii PKO1 converted nitrobenzene to 3- and 4-nitrocatechol via 3- and 4-nitrophenol. The nitrocatechols were slowly degraded to unidentified metabolites. Nitrobenzene did not serve as an inducer for the enzymes that catalyzed its oxidation. These results indicate that the nitrobenzene ring is subject to initial attack by both mono- and dioxygenase enzymes.     

The 3'' untranslated regions of two related mRNAs contain an element highly repeated in the sea urchin genome.

Two closely related cDNA clones, pSpec1 and pSpec2, specifying two developmentally regulated tissue specific mRNAs from sea urchin embryos were used to probe a sea urchin genomic lambda library. Screening 10,000 phage by plaque hybridization yielded several hundred positive signals. With more stringent wash procedures, only two to three phage were positive. Three of these phage, one isolated by stringent wash procedures and two isolated by standard wash procedures were further investigated by restriction analysis, RNA gel blots, and DNA sequencing. The phage isolated by the stringent wash procedure appears to be a gene coding for the Specl mRNA. The other phage contain only partial homology to pSpec1 and pSpec2, 150 to 200 base pairs of the 3' untranslated region of the Spec1 and Spec2 mRNAs. It is concluded that the Spec1 and Spec2 mRNAs contain a highly repetitive element near their 3' end. The element is present at 2000 to 3000 copies per genome and may be transcribed at some sites other than those coding for the Spec1 and Spec2 genes. The possible function and evolutionary origin of the repetitive element is discussed.