Biodegradable plastics are currently being developed as a short-term solution to the problem of conventional plastics which persist in the soil. Little is known regarding the decomposition of the new plastics including products formed and microbial populations responsible.Polyethylene-based plastic films interspersed with 0, 5, 10 or 15% (w/w) starch were incubated for up to 112 days in laboratory and filed soils, a forced-air compost pile, and a simulated sanitary landfill. Biologically-mediated polymer decomposition was monitored via measurement of microbial respiration, release of soluble organic carbon ()C) and anions, total microbial counts, and scanning electron microscopic (SEM) observations. Microbial respiration was greatest in all treatments within the first 14 days coincided with greatest soluble OC and acid production.The 15% starch samples decomposed most rapidly in the field soils (2.57. decrease in mass over 11 days) due to the influence of sunlight and temperature extremes. Decomposition was lowest (0.1%) in the anaerobic landfill.Actinomycetes and bacteria predominated in most environments while fungi growth was inhibited in the landfill and compost. The SEM observations revealed a preferential attack of starch granules by microbes followed by a more gradual weathering of polyethylene sheets. / Department of Natural Resources

No description available.

Thesis (M. S. - Hydrology and Water Resources)--University of Arizona, 2000. / Includes bibliographical references (leaves 48-51).

Thesis (Ph. D.)--Carleton University, 1993. / Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

Cyanides enter the environment through both natural and man-made sources. Natural sources include cyanogenesis by bacteria, fungi and plants. A number of cyanide catabolising microorganisms have also been reported in literature. This is the first reported instance of cyanide catabolism in Trichoderma harzianum. Four strains of T. harzianum, one of T. pseudokoningii were evaluated. An investigation was made into the occurrence and distribution of the cyanide catabolising enzymes. Three enzymes, cyanide hydratase, beta-cyanoalanine synthase and rhodanese, were studied. All the strains showed a high capacity to degrade cyanide via both the cyanide hydratase and rhodanese pathways, beta-cyanoalanine synthase activity, however, was not detected in any of the selected strains. In the studies on the kinetic characterization of the rhodanese enzyme, a broad pH optimum of 8.5 - 10.5 was obtained for all the strains and a broad temperature optimum of 35 - 55 °C was also observed. The KmCN and Vmax values ranged from 7-16 mM and from 0.069 - 0.093 betamoles. Min-1. mg protein-1, respectively, between the selected strains of Trichoderma. Strong evidence of cyanide biodegradation and co-metabolism emerged from studies with flask cultures where glucose was provided as a co-substrate. The rate of degradation of 2000 ppm CIST was enhanced almost three times in the presence of glucose. Plant microcosm studies carried out using pea and wheat seeds too gave further corroboration of the cyanide degrading and plant growth promotion capabilities of Trichoderma. Microcosms set-up with cyanide at 50 or 100 ppm CN, in the presence of Trichoderma, showed germination of both pea and wheat seeds. There was no seed germination in any of the controls in the absence of Trichoderma inoculation.

Microbial aromatic compound degradation often involves carbon-carbon bond hydrolysis of a meta-cleavage product (MCP). BphDLB400 (EC 3.7.1.8), the MCP hydrolase from the biphenyl degradation pathway of Burkholderia xenovorans LB400, hydrolyzes 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate (HOPDA) to 2-hydroxypenta-2,4-dienoate (HPD) and benzoate. Although MCP hydrolases contain the catalytic triad (Ser112-His265-Asp237) and structural fold of the α/β-hydrolase superfamily, previous studies suggest they deviate from the classical hydrolytic mechanism in two respects: (1) enol-keto tautomerization precedes hydrolysis and (2) hydrolysis involves a gem-diol intermediate. Stopped-flow kinetic studies revealed rapid accumulation of a transient intermediate possessing a red-shifted absorption spectrum (λmax = 492 nm) versus HOPDA (λmax = 434 nm), consistent with an enzyme-bound, strained enolate (E:Sse). In studies with BphDLB400 variants, S112A trapped the E:Sse intermediate, implying that Ser112 is required for subsequent tautomerization and hydrolysis. His265 is required for E:Sse formation, as H265A variants instead generated a species assigned to a non-strained HOPDA enolate, which was not spectroscopically observed in the WT enzyme. The proposed importance of double bond strain in the reaction was supported by crystallographic observation of a non-planar, strained substrate in the S112A:HOPDA complex. Inhibition of BphDLB400 by 3-Cl HOPDA was investigated to understand a block in the degradation of polychlorinated biphenyls. BphDLB400 preferentially hydrolyzed 3-substituted HOPDAs in the order H > F > Cl > Me, indicating that steric bulk impairs catalysis. Kinetic analyses further indicated that large 3-substituents impede formation of the strained enolate by binding in an alternate conformation, as observed in the S112A:3-Cl HOPDA crystal structure. Finally, rate-determining hydrolysis of a benzoyl-enzyme was suggested from the observations that: (i) HOPDA and p-nitrophenyl benzoate were transformed with similar kcat values and (ii) yielded a common product ratio in the presence of methanol. Overall, the studies demonstrate the importance of an intermediate possessing significant double bond strain in an MCP hydrolase, establish the role of the catalytic His in forming this intermediate, indicate a mechanism of inhibition, and suggest the possibility that hydrolysis may proceed via an acyl-enzyme. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

No description available.

No description available.

No description available.