A mechanistic perspective on bacterial metabolism of chlorinated methanes

Chlorinated methanes are important environmental pollutants, which can be metabolized by bacteria. The biotransformation of chlorinated methanes by bacteria has been shown to be due either to gratuitous metabolism (cometabolism) or their use as a source of carbon and energy. The reactions which result in carbon-halogen bond cleavage include substitutive, reductive, oxygenative, and gem-elimination mechanisms. Certain methylotrophic bacteria can use dichloromethane as a source of carbon and energy. Dichloromethane dehalogenase catalyzes the first substitutive reaction in this metabolism. The enzyme shows a 10¹⁰-fold rate enhancement over the reaction of the bisulfide anion with dichloromethane in water. Pseudomonas putida G786 synthesizes cytochrome P-450_CAM which catalyzes the gratuitous reduction of chlorinated methanes. These studies with purified enzymes are beginning to reveal more detailed mechanistic features of bacterial chlorinated methane metabolism.Abbreviations DNA deoxyribonucleic acid - k_cat catalytic first order rate constant for an enzyme catalyzed reaction - K_M Michaelis constant for an enzyme catalyzed reaction - MNDO modified neglect of diatomic overlap - PIMA pattern induced multialignment - DCMD dichloromethane dehalogenase     

Changes in soil microflora associated with control of Sclerotium Rolfsii by Furfuraldehyde

The efficacy of 2‐furfuraldehyde for control of Sclerotium rolfsii was studied in laboratory and greenhouse experiments. Mycelial growth of the fungus was reduced proportionally with concentrations of 0.1–0.5 ml furfuraldehyde l^‐1 agar medium, and viability of sclerotia diminished on exposure to 2‐furfuraldehyde vapours. Detectable populations of bacteria and fungi, including Trichoderma spp., were reduced significantly (9=0.05) when furfuraldehyde was added to the agar used for soil dilution plates of untreated soil. Repeated treatments of natural soil with the fumigant significantly increased populations of Trichoderma spp. and bacteria, but diminished numbers of actinomycetes. Increasing dosages applied to soil artificially infested with S. rolfsii caused a reduction of disease on lentil, Lens culinaris. Results indicate that the compound, when applied to field soil, changes the composition of soil microflora and has potential for integrated control of S. rolfsii.     

A Comparison of the Efficacy of Nuclear Polyhedrosis and Granulosis Viruses in Spray and Bait Formulations for the Control of Agrotis segetum (Lepidoptera: Noctuidae) in Maize

Agrotis segetum nuclear polyhedrosis virus (AsNPV) and granulosis virus (AsGV), propagated in laboratory cultures of A. segetum in England and A. ipsilon in Spain, respectively, were applied to plots of maize plants at the one‐ to four‐leaf stage of growth. Plots were arranged in a 6 x 6 Latin square design and infested with second‐instar A. segetum larvae (the common cutworm). Each virus was applied in separate treatments by two application methods; as an aqueous spray containing 0.1% Agral as a wetting agent, and as a bran bait. The NPV was applied at a rate of 4 X 10¹² polyhedra/ha, and the GV at 4 X 10¹³ granules/ha. Soil and plants were sampled for larvae on three occasions following virus treatment: 24 h, 4 days and 11 days. The larvae were reared on diet in the laboratory, until death or pupation, to examine the rate and level of viral infection. Infection data showed 87.5% and 91% NPV infection and 12.5% and 55% GV infection in spray and bait treatments, respectively, in larvae sampled 24 h after treatment. In larvae sampled 4 days after treatment, the results were 78% and 100% NPV infection, and 13% and 6% GV infection. A total of only six larvae were retrieved on day 11. In both treatments larvae infected with AsNPV died significantly more rapidly and at an earlier instar than those infected with AsGV, indicating that AsNPV appears to have better potential as a control agent for A. segetum.     

Studies on anabolic steroids--12. Epimerization and degradation of anabolic 17 beta-sulfate-17 alpha-methyl steroids in human: qualitative and quantitative GC/MS analysis.

The epimerization and dehydration reactions of the 17 beta-hydroxy group of anabolic 17 beta-hydroxy-17 alpha-methyl steroids have been investigated using the pyridinium salts of 17 beta-sulfate derivatives of methandienone 1, methyltestosterone 4, oxandrolone 7, mestanolone 10 and stanozolol 11 as model compounds. Rearrangement of the sulfate conjugates in buffered urine (pH 5.2) afforded the corresponding 17-epimers and 18-nor-17,17-dimethyl-13(14)-enes in a ratio of 0.8:1. These data indicated that both epimerization and dehydration of the 17 beta-sulfate derivatives were not dependent upon the respective chemical features of the steroids studied, but were instead inherent to the chemistry of the tertiary 17 beta-hydroxy group of these steroids. Interestingly, in vivo studies carried out with human male volunteers showed that only methandienone 1, methyltestosterone 4 and oxandrolone 7 yielded the corresponding 17-epimers 2, 5 and 8 and the 18-nor-17,17-dimethyl-13(14)-enes 3, 6 and 9 in ratios of 0.5:1, 2:1 and 2.7:1, respectively. No trace of the corresponding 17-epimers and 18-nor-17,17-dimethyl-13(14)-enes derivatives of mestanolone 10 and stanozolol 11 was detected in urine samples collected after administration of these steroids. These data suggested that the in vivo formation of the 17-epimers and 18-nor-17,17-dimethyl-13(14)-enes derivatives of 17 beta-hydroxy-17 alpha-methyl steroids is also dependent upon phase I and phase II metabolic reactions other than sulfation of the tertiary 17 beta-hydroxyl group, which are probably modulated by the respective chemical features of the steroidal substrates. The data reported in this study demonstrate that the 17-epimers and 18-nor-17,17-dimethyl-13(14)-enes are not artifacts resulting from the acidic or microbial degradation of the parent steroids in the gut as previously suggested by other authors, but arise from the rearrangement of their 17 beta-sulfate derivatives. Unchanged oxandrolone 7 was solely detected in the unconjugated steroid fraction whereas unchanged steroids 1, 4 and 11 were recovered from the glucuronide fraction. These data are indirect evidences suggesting that the glucuronide conjugates of compounds 1 and 4 are probably enol glucuronides and that of compound 11 is excreted in urine as a N-glucuronide involving its pyrazole moiety. The urinary excretion profiles of the epimeric and 18-nor-17,17-dimethyl-13(14)-ene steroids are presented and discussed on the basis of their structural features.     

湖泊和地下水中异养细菌群落结构和生理特征的比较研究

对武汉东湖三个定点观测站和潜江市一深水机井中异养细菌群落的种群组成、对不同基质的反应、菌株和群落的生理特征和活力水平等方面比较研究结果表明:环境差异较小的东湖Ⅰ、Ⅱ、Ⅲ站异养细菌群落间的差异亦较小,具有类似的结构特征和生理活力水平,对特定基质表现了相似的作用模式;地下水中的异养细菌群落在上述几方面均显示了明显的差别。此外,在异养细菌群落结构和功能研究方法上亦是有益的探讨。     

青龙河底栖无脊椎动物群落结构及其水质评价

本文论述了青龙河底栖生物种类、数量、分布和结构等特点及其与环境因子间的关系。应用Beck、Gleason、Shannon、Simpson等生物指数对水质状况进行评价。结果表明青龙河除个别断面受污染外,大部分河段属尚清洁水。