W. Jack Jones

Microbial Transformation of Triadimefon to Triadimenol in Soils: Selective Production Rates of Triadimenol Stereoisomers Affect Exposure and Risk

The microbial transformation of triadimefon, an agricultural fungicide of the 1,2,4-triazole class, was followed at a nominal concentration of 50 μg/mL over 4 months under aerobic conditions in three different soil types. Rates and products of transformation were measured, as well as enantiomer fractions of parent and products. The transformation was biotic and enantioselective, and in each soil the S-(+)-enantiomer reacted faster than the R-(-) one. Rates of the first-order reactions were 0.047, 0.057, and 0.107 d(-1) for the three soils. The transformation involves reduction of the prochiral ketone moiety of triadimefon to an alcohol, resulting in triadimenol, which has two chiral centers and four stereoisomers. The abundances of the four product stereoisomers were different from each other, but abundance ratios were similar for all three soil types. Triadimenol is also a fungicide; the commercial product is composed of two diastereomers of unequal amounts (ratio of about 4.3:1), each having two enantiomers of equal amounts. However, the triadimenol formed by soil transformation of triadimefon exhibited no such stereoisomer profile. Instead, different production rates were observed for each of the four triadimenol stereoisomers, resulting in all stereoisomer concentrations being different from each other and very different from concentration/abundance patterns of the commercial standard. This result is important in risk assessment if the toxicity of the environmental transformation product were to be compared to that of the commercial triadimenol. Because triadimenol stereoisomers differ in their toxicities, at least to fungi and rats, the biological activity of the triadimenol formed by microbes or other biota in soils depends on the relative abundances of its four stereoisomers. This is an exposure and risk assessment issue that, in principle, applies to any chiral pesticide and its metabolites.

Biochemical and phylogenetic characterization of two novel deep-sea Thermococcus isolates with potentially biotechnological applications

Abstract The partial 16S rDNA gene sequences of two thermophilic archaeal strains, TY and TYS, previously isolated from the Guaymas Basin hydrothermal vent site were determined. Lipid analyses and a comparative analysis performed with 16S rDNA sequences of similar thermophilic species showed that the strains isolated from deep-sea vents were not identical to the other species belonging to the genus Thermococcus. On the basis of the results of the phylogenetic analyses, lipid analyses, and previously reported physiological data, we believe that strains TY and TYS are significantly different from the previously described Thermococcus species. According to specific physiological and molecular features, we propose the use of these isolates as potential tools for the development of biotechnological applications in the field of starch processing and DNA technology.

Biotransformation of quinoline and methylquinolines in anoxic freshwater sediment

Quinoline (Q) and some isomers of methylquinoline (MQ) were transformed to hydroxylated products in freshwater sediment slurries incubated under methanogenic conditions at 25 °C. Methylquinoline transformation was not affected by a methyl group on the C-3 or C-4 carbon atom of the pyridine ring; 2-MQ, however, was not transformed. All isomers of dimethylquinoline (DMQ) tested (2,4-, 2,6-, 2,7-, and 2,8-DMQ) with a methyl group at the number 2 carbon also persisted in sediments after anaerobic incubation for one year at 25 °C.In most experiments, quinoline initially was transformed to 2-hydroxyquinoline (2-OH-Q), which was further metabolized to unidentified products. A second product, 4-CH3-2-OH-Q, was detected in some experiments. This product accumulated and was not further transformed. 6-, 7-, and 8-Methylquinoline (6-, 7-, 8-MQ) were hydroxylated to form the respective 2-OH-MQ products. These hydroxylated products accumulated and were not further transformed. Hydroxylation of Q and 6-, 7- and 8-MQ at the 2-carbon position was confirmed by GC/FTIR and GC/MS analyses. The transformations of Q and MQs were pH dependent with an optimal pH of 7–8.The results of this study suggest that two pathways may exist for the anaerobic transformation of quinoline; one pathway leads to the formation of a hydroxylated intermediate and the other to a methylated and hydroxylated intermediate. In addition, our results suggest that a methyl substituent on the number 2 carbon inhibits the anaerobic transformation of quinoline derivatives.

H2 consumption during the microbial reductive dehalogenation of chlorinated phenols and tetrachloroethene.

Competition for molecular hydrogen exists amonghydrogen-utilizing microorganismsin anoxic environments, and evidence suggeststhat lower hydrogen concentrations areobserved with more energetically favorableelectron-accepting processes. The transferof electrons to organochlorines via reductivedehalogenation reactions plays an importantrole in hydrogen dynamics in impacted systems. Westudied the flux of aqueous hydrogenconcentrations in methanogenic sediment microcosmsprior to and during reductivedehalogenation of a variety of substituted chlorophenols(CP) and tetrachloroethene(perchloroethylene, PCE). Mean hydrogen concentrationsduring reductive dehalogenationof 2,4-CP, 2,3,4-CP, and PCP were 3.6 nM, 4.1 nM,and 0.34 nM, respectively. Sedimentmicrocosms that were not dosed with chlorophenolsyet were actively methanogenicmaintained a significantly higher mean hydrogenconcentration of 9.8 nM. Duringactive PCE dehalogenation, sediment microcosmsmaintained a mean hydrogenconcentration of 0.82 nM. These data indicate thatduring limiting hydrogen production,the threshold ecosystem hydrogen concentration iscontrolled by microbial populationsthat couple hydrogen oxidation to thermodynamicallyfavorable electron acceptingreactions, including reductive dehalogenationof chloroaromatic compounds. Wealso present revised estimates for the Gibbsfree energy available from the reductivedehalogenation of a variety of substitutedchlorophenols based on recently publishedvalues of vapor pressure, solubility, and pKafor these compounds.

Estimation of microbial reductive transformation rates for chlorinated benzenes and phenols using a quantitative structure-activity relationship approach.

A set of literature data was used to derive several quantitative structure-activity relationships (QSARs) to predict the rate constants for the microbial reductive dehalogenation of chlorinated aromatics. Dechlorination rate constants for 25 chloroaromatics were corrected for the effects of hydrophobic partitioning and adjusted for the observed distribution of product species. A number of physicochemical properties and molecular parameters were considered for inclusion in the QSARs. Multivariate statistical analyses were used to select the optimal set of descriptors to minimize multicollinearity between the descriptors, as well as to minimize the p-value of the regression coefficients. The final QSAR included four descriptors: The logarithm of the octanol-water partition coefficient (Kow), the summation of the Hammett sigma constants, and the sigma induction constants in the ortho and meta positions relative to the transformation reaction center. The predictive ability of this QSAR was evaluated using 24 site-specific rate constants that were measured in five separate studies and were not used to derive the expression. The peer-reviewed literature was screened carefully to ensure that all rate constant data were representative of environmentally relevant conditions.

Prediction of Hydrolysis Products of Organic Chemicals under Environmental pH Conditions

Cheminformatics-based software tools can predict the molecular structure of transformation products using a library of transformation reaction schemes. This paper presents the development of such a library for abiotic hydrolysis of organic chemicals under environmentally relevant conditions. The hydrolysis reaction schemes in the library encode the process science gathered from peer-reviewed literature and regulatory reports. Each scheme has been ranked on a scale of one to six based on the median half-life in a data set compiled from literature-reported hydrolysis rates. These ranks are used to predict the most likely transformation route when more than one structural fragment susceptible to hydrolysis is present in a molecule of interest. Separate rank assignments are established for pH 5, 7, and 9 to represent standard conditions in hydrolysis studies required for registration of pesticides in Organisation for Economic Co-operation and Development (OECD) member countries. The library is applied to predict the likely hydrolytic transformation products for two lists of chemicals, one representative of chemicals used in commerce and the other specific to pesticides, to evaluate which hydrolysis reaction pathways are most likely to be relevant for organic chemicals found in the natural environment.