Tolerance to trichlorophenols in microorganisms from a polluted and a pristine site of a river

An essential esterase (BroH) for the mineralization of bromoxynil octanoate by a natural consortium of Sphingopyxis sp. strain OB-3 and Comamonas sp. strain 7D-2

A natural consortium of two bacterial strains ( Sphingopyxis sp. OB-3 and Comamonas sp. 7D-2) was capable of utilizing bromoxynil octanoate as the sole source of carbon for its growth. Strain OB-3 was able to convert bromoxynil octanoate to bromoxynil but could not use the eight-carbon side chain as its sole carbon source. Strain 7D-2 could not degrade bromoxynil octanoate, although it was able to mineralize bromoxynil. An esterase (BroH) that is involved in the conversion of bromoxynil octanoate into bromoxynil and is essential for the mineralization of bromoxynil octanoate by the consortium was isolated from strain OB-3 and molecularly characterized. BroH encodes 304 amino acids and resembles α/β-hydrolase fold proteins. Recombinant BroH was overexpressed in Escherichia coli BL21 (DE3) and purified by Ni-NTA affinity chromatography. BroH was able to transform p-nitrophenyl esters (C2-C14) and showed the highest activity toward p-nitrophenyl caproate (C6) on the basis of the catalytic efficiency value (Vmax/Km). Additionally, BroH activity decreased when the aliphatic chain length increased. The optimal temperature and pH for BroH activity was found to be 35 °C and 7.5, respectively. On the basis of a phylogenetic analysis, BroH belongs to subfamily V of bacterial lipolytic enzymes.

PAH mineralization and bacterial organotolerance in surface sediments of the Charleston Harbor estuary

Semi-volatile organic compounds (SVOCs) in estuarine waters can adversely affect biota but watershed sources can be difficult to identify because these compounds are transient. Natural bacterial assemblages may respond to chronic, episodic exposure to SVOCs through selection of more organotolerant bacterial communities. We measured bacterial production, organotolerance and polycyclic aromatic hydrocarbon (PAH) mineralization in Charleston Harbor and compared surface sediment from stations near a known, permitted SVOC outfall (pulp mill effluent) to that from more pristine stations. Naphthalene additions inhibited an average of 77% of bacterial metabolism in sediments from the more pristine site (Wando River). Production in sediments nearest the outfall was only inhibited an average of 9% and in some cases, was actually stimulated. In general, the stations with the highest rates of bacterial production also were among those with the highest rates of PAH mineralization. This suggests that the capacity to mineralize PAH carbon is a common feature amongst the bacterial assemblage in these estuarine sediments and could account for an average of 5.6% of bacterial carbon demand (in terms of production) in the summer, 3.3% in the spring (April) and only 1.2% in winter (December).

C. fumago chloroperoxidase is also a dehaloperoxidase: oxidative dehalogenation of halophenols

We have examined the H2O2-dependent oxidative dehalogenation of 2,4,6-trihalophenols and p-halophenols catalyzed by Caldariomyces fumago chloroperoxidase (CCPO). CCPO is significantly more robust than other peroxidases and can function under harsher reaction conditions, and so its ability to dehalogenate halophenols could lead to its use as a bioremediation catalyst for aromatic dehalogenation reactions. Optimal catalysis occurred under acidic conditions (100 mM potassium phosphate solution, pH 3.0). UV-visible absorption spectroscopy, high-performance liquid chromatography, and gas chromatography/mass spectrometry clearly identified the oxidized reaction product for CCPO-catalyzed dehalogenation of 2,4,6-trihalophenols as the corresponding 2,6-dihalo-1,4-benzoquinones. This reaction has previously been reported for two His-ligated heme-containing peroxidases (see Osborne, R. L.; Taylor, L. O.; Han, K. P.; Ely, B.; Dawson, J. H. Biochem. Biophys. Res. Commun. 2004, 324, 1194-1198), but this is the first example of a Cys-ligated heme-containing peroxidase functioning as a dehaloperoxidase. The relative catalytic efficiency (turnover number) of CCPO reported herein is comparable to that of horseradish peroxidase (Ferrari, R. P.; Laurenti, E.; Trotta, F. J. Biol. Inorg. Chem. 1965, 4, 232-237). The mechanism of dehalogenation has been probed using p-halophenols as substrates. Here the major product is a dimer with 1,4-benzoquinone as the minor product. An electron-transfer mechanism is proposed that accounts for the products formed from both the 2,4,6-trihalo- and p-halophenols. Finally, we note that this is the first case of a peroxidase known primarily for its halogenation ability being shown to also dehalogenate substrates.

Biosynthesis of poly-beta-hydroxyalkanoates by Sphingopyxis chilensis S37 and Wautersia sp. PZK cultured in cellulose pulp mill effluents containing 2,4,6-trichlorophenol

Poly-beta-hydroxyalkanoates (PHA) polymer is synthesized by different bacterial species. There has been considerable interest in the development and production of biodegradable polymers; however, the high cost of PHA production has restricted its applications. Kraft cellulose industry effluents containing 2,4,6-trichlorophenol (10 or 20 microg ml(-1)) were used by the bacteria Sphingopyxis chilensis S37 and Wautersia sp. PZK to synthesize PHA. In this condition, S. chilensis S37 was able to grow and degrade 2,4,6-trichlorophenol (ca. 60%) and 80% of these cells accumulated PHA. Wautersia PZK completely degraded 2,4,6-TCP and more than 90% of the cells accumulated PHA in 72 h. The PHA detection was performed by flow cytometry and polyester composition was characterized by gas chromatography-mass spectroscopy (GC-MS), indicating that these polymers are made by 3-hydroxybutyric acid and 3-hydroxyhexadecanoic acid for S37 and PZK strains, respectively. Results demonstrated that strains' growth and PHA production and composition are not modified in cellulose effluents with or without 2,4,6-TCP (10-20 microg ml(-1)). Therefore, our results indicate that S. chilensis S37 and Wautersia sp. PZK are able to degrade a toxic compound such as a 2,4,6-TCP and simultaneously produce a valuable biopolymer using low-value substrates.

Oxidation of 2,4-dichlorophenol catalyzed by horseradish peroxidase: characterization of the reaction mechanism by UV-visible spectroscopy and mass spectrometry

The hydrogen peroxide-oxidation of 2,4-dichlorophenol catalyzed by horseradish peroxidase has been studied by means of UV-visible spectroscopy and mass spectrometry in order to clarify the reaction mechanism. The dimerization of 2,4-dichlorophenol to 2,4-dichloro-6-(2,4-dichlorophenoxy)-phenol and its subsequent oxidation to 2-chloro-6-(2,4-dichlorophenoxy)-1,4-benzoquinone together with chloride release were observed. The reaction rate was found to be pH-dependent and to be influenced by the pK(a) value of 2,4-dichlorophenol. The dissociation constants of the 2,4-dichlorophenol/horseradish peroxidase (HRP) adduct at pH 5.5 and 8.5 were also determined: their values indicate the unusual stability of the adduct at pH 5.5 with respect to several adducts of HRP with substituted phenols.

Sphingopyxis chilensis sp. nov., a chlorophenol-degrading bacterium that accumulates polyhydroxyalkanoate, and transfer of Sphingomonas alaskensis to Sphingopyxis alaskensis comb. nov

The taxonomic position of a chlorophenol-degrading bacterium, strain S37T, was investigated. The 16S rDNA sequence indicated that this strain belongs to the genus Sphingopyxis, exhibiting high sequence similarity to the 16S rDNA sequences of Sphingomonas alaskensis LMG 18877T (98.8%), Sphingopyxis macrogoltabida LMG 17324T (98.2%), Sphingopyxis terrae IFO 15098T (95%) and Sphingomonas adhaesiva GIFU 11458T (92%). These strains (except Sphingopyxis terrae IFO 15098T, which was not investigated) and the novel isolate accumulated polyhydroxyalkanoates consisting of 3-hydroxybutyric acid and 3-hydroxyvaleric acid from glucose as carbon source. The G + C content of the DNA of strain S37T was 65.5 mol%. The major cellular fatty acids of this strain were octadecenoic acid (18 : 1omega7c), heptadecenoic acid (17 : 1omega6c) and hexadecanoic acid (16 : 0). The results of DNA-DNA hybridization experiments and its physiological characteristics clearly distinguished the novel isolate from all known Sphingopyxis species and indicated that the strain represents a novel Sphingopyxis species. Therefore, the species Sphingopyxis chilensis sp. nov. is proposed, with strain S37T (=LMG 20986T =DSM 14889T) as the type strain. The transfer of Sphingomonas alaskensis to the genus Sphingopyxis as Sphingopyxis alaskensis comb. nov. is also proposed.

Enzymatic degradation of 2,6-dichlorophenol by horseradish peroxidase: UV-visible and mass spectrometry characterization of the reaction products [corrected]

The reaction mechanism of the oxidation of 2,6-dichlorophenol (2,6-DCP) by horseradish peroxidase (HRP) and H2O2 has been investigated and the reaction products have been characterized by UV-visible and mass spectrometry. Evidence for the dimerization of 2,6-DCP to 3,3',5,5'-tetrachloro-4,4'-dihydroxybiphenyl and the subsequent fast oxidation of this product to the corresponding 3,3',5,5'-tetrachlorodiphenoquinone have been collected. The reaction rate was found to decrease markedly as soon as the pH was raised, with a clear inflection point at pH congruent with 6.6-6.9; it also resulted independent from H2O2 concentration. Since the pK(a) for 2,6-DCP is 6.80, the reaction rate might be influenced by the protonation state of the substrate.

Bacterial response to photocatalytic degradation of 6-chlorovanillin

The oxidation of a 186 ppm 6-chlorovanillin solution was performed using impregnated TiO2 glass rings in a 1 l photochemical reactor. Fifty per cent degradation was obtained after 60 min with recirculation of the solution. Then, oxidised samples were submitted under aerobic conditions to bacterial degradation in the Pseudomonas paucimobilis (S37) and Burkholderia cepacia (PZK). Both selected aerobic bacteria degrade more efficiently the photocatalysed samples, being PZK strain better than S37. A first-order kinetic was observed in both systems photocatalytic and bacterial degradation.