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Biomedical subjects

D L Lewis

Publications and source records attributed to D L Lewis.

At least 73 records · Page 4Linked to original sources
PubMed1986

Nutrient limitation and adaptation of microbial populations to chemical transformations.

Using field-collected periphyton and bacterial isolates, we determined adaptation lag periods for microbial transformation of p-cresol. Lag periods were longer for periphyton samples collected from field sites that were low in dissolved inorganic nitrogen and phosphorus. Moreover, lag periods decreased in samples amended with N or P. Our data suggest that adaptation lag periods for microbial transformation of low concentrations of chemicals may correlate with limiting nutrient concentrations, and this correlation may provide a basis for predictive mathematical modeling of lag periods.

Journal Article↗
PubMed1986

T cell receptor gene rearrangements define a monoclonal T cell proliferation in patients with T cell lymphocytosis and cytopenia.

We have used probes from the T cell receptor beta and gamma chain loci to investigate the clonality of T lymphocytes in eight patients with T cell lymphocytosis and cytopenia (TCLC). This syndrome, which is strongly associated with rheumatoid arthritis, is characterized by peripheral blood and bone marrow lymphocytosis and neutropenia, red cell aplasia, or both. By means of T cell monoclonal antibodies and flow cytometry, T lymphocytes from patients with this syndrome have been shown to have characteristic immunologic features. Investigators have disagreed as to whether the syndrome represents a T cell malignancy or a more benign immunologic disorder. DNA from five of five patients with symptomatic "classic" T cell lymphocytosis with cytopenia demonstrated unique rearrangements of the T cell receptor beta chain locus, whereas neither of two patients with atypical features showed rearrangement. In addition, we found evidence for gamma chain rearrangement in those DNAs with clonal beta chain rearrangement. We thus postulate that the classic form of this syndrome is associated with a monoclonal proliferation of T cells. Its potential relationship to T cell chronic lymphocytic leukemia is discussed.

Aged↗
PubMed1985

Multiphasic kinetics for transformation of methyl parathion by flavobacterium species.

Transformation rates of an insecticide, methyl parathion, in pure cultures of Flavobacterium sp. followed multiphasic kinetics involving at least two systems (I and II). System I was a high-affinity, low-capacity system, and system II was a low-affinity, high-capacity system. Data from rate experiments suggested that metabolites formed via system II inhibited system I such that only one system operated at a time. System I operated at approximately 20 mug liter and less; system II operated at approximately 4 mg liter and less. These results show that xenobiotic chemicals, like naturally occurring substrates, can be transformed via multiple uptake and transformation systems even by a pure culture. Furthermore, computer simulation models of pollutant transformation rates based on kinetic constants determined in this study show that large errors can occur in predicted rates when the multiphasicity of kinetics is neglected.

Journal Article↗
PubMed1984

Effects of microbial community interactions on transformation rates of xenobiotic chemicals.

The effects of culture filtrates, mixed populations, and common microbial exudates on bacterial transformations of three agricultural and industrial chemicals were investigated. Test chemicals included methyl parathion, diethyl phthalate, and 2,4-dichlorophenoxyacetic acid butoxyethyl ester. The presence of various cultures, filtrates, or exudates of algae, fungi, or other bacteria either stimulated or inhibited bacterial transformation rates. Inhibition resulted from treatments that lowered the pH, and stimulation resulted from an increase in cell biomass (based on plate counts) and from a different process whereby rates of transformation per bacterial cell rapidly increased as much as 10-fold.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1983

Predicting 2,4-dichlorophenoxyacetic Acid ester transformation rates in periphyton-dominated ecosystems.

Using batch cultures, we determined transformation rate coefficients for microbial transformation of 2,4-dichlorophenoxyacetic acid butoxyethyl ester (2,4-DBE) in periphyton-dominated ecosystems. Rates of 2,4-DBE loss were measured over short periods of time (usually less than 10 h), and first-order transformation rate coefficients (k(1)) were determined under the specific conditions of low 2,4-DBE concentrations and no growth. Values for k(1) were divided by total plate counts and by biomass measured as ash-free dry weight to give second-order rate coefficients (k(b) and k(AFDW), respectively) for use in predictive models. Using periphyton attached to Teflon strips, we also determined second-order rate coefficients based on the ratio of colonized surface area to container volume (k(A)). Mean second-order rate coefficients were used to predict 2,4-DBE transformation rates in microcosms having diverse chemical and biological environments. The observed transformation rates among the microcosms were most accurately predicted by using k(A).

Journal Article↗
PubMed1981

Rates of transformation of methyl parathion and diethyl phthalate by aufwuchs microorganisms.

Using batch cultures, we determined transformation rates for low concentrations of two toxicants-an insecticide, methyl parathion (O,O-dimethyl O-p-nitrophenyl phosphorothioate), and a plasticizer, diethyl phthalate-by aufwuchs, aquatic microbial growth attached to submerged surfaces or suspended in streamers or mats. Aufwuchs samples were collected from field sites, an indoor channel, and a continuous-flow fermentor. Aufwuchs fungi, protozoa, and algae did not transform methyl parathion or diethyl phthalate, but bacteria rapidly transformed both chemicals. Second-order transformation rate coefficients, K(b), based on total plate counts of bacteria in aufwuchs, were determined for potential use in a mathematical model capable of predicting the transport and fate of chemicals in aquatic systems. K(b) for both methyl parathion and diethyl phthalate decreased as the concentration of total bacteria, [B], increased in aufwuchs. This effect resulted from the proportion of nontransformer to transformer bacteria increasing as [B] increased and from the rate of transformation per transformer cell decreasing as [B] increased. First-order transformation rate coefficients, K(1), were relatively stable per unit of surface area colonized by aufwuchs, because K(b) decreased as [B] increased (K(1) = K(b) x [B]).

Journal Article↗
PubMed1976

The protein composition of bovine myelin-free axons.

The proteins of axons prepared from myelinated axons and isolated as myelin-free entities were separated by sodium dodecyl sulfate polyacrylamide electrophoresis and found to consist of more than 10 different molecular weight species. The molecular weights range from 13 000 to over 200 000 with a prominent protein of molecular weight 47 000. The amino acid composition of the seven major proteins showed that the protein with a molecular weigt of 47 000 is distinct from all the other proteins analyzed. A group of three low molecular weight proteins have amino acid compositions which are similar to each other as do a group of three high molecular weight proteins although the two groups are distinctly different from each other and the major axonal protein. Histones, DNA, myelin basic protein and glycoprotein were absent from the proteins but neurotubule protein was present as indicated by cochicine binding activity in the axonal preparations. The cellular origin of these proteins and their relationship to other central nervous system proteins are discussed.

Amino Acids↗
PubMed1972

Vagotomy and pyloroplasty for gastric ulcer.

In a series of 68 patients with gastric ulcer who were treated by vagotomy and pyloroplasty there were no operative deaths, though one patient who received massive transfusions died 14 weeks later from hepatic necrosis probably associated with serum hepatitis. Four patients developed recurrent peptic ulceration requiring further surgical treatment. The clinical condition of all but three of the remainder was satisfactory after an average follow-up period of three years and two months. Of the 14 patients who presented with an acutely bleeding gastric ulcer, one subsequently required gastrectomy for continued bleeding; in all the others the immediate and long-term results were satisfactory. Of 21 patients with a "high" ulcer and 29 with combined gastric and duodenal ulceration one (4.8%) and three (10%) respectively suffered recurrences. We conclude that vagotomy and pyloroplasty is a satisfactory form of treatment for a high or bleeding gastric ulcer, but that for all other gastric ulcers some form of gastric resection is preferable.

Adult↗