Biomedical subjects

Daniel Smith

Publications and source records attributed to Daniel Smith.

21 records · Page 2Linked to original sources

PubMed2003

Impact of the plant rhizosphere and augmentation on remediation of polychlorinated biphenyl contaminated soil.

This study investigated the interactive effects of bioaugmentation, biostimulation, and the rhizosphere during remediation of Aroclor 1242-contaminated soil. Treatments were repeatedly augmented with polychlorinated bipheny (PCB)-degrading bacteria, inducers (carvone and salicylic acid), surfactant (sorbitan trioleate), minimal salts medium in a 20-cm high soil column, or a combination of these elements. Soils containing a single Brassica nigra plant achieved 61% PCB removal in the 0 to 2 and 2 to 6 cm depths after 9 weeks of bioaugmentation, whereas only 43 and 14% PCB removal, respectively, was achieved in unplanted controls. Gas diffusion coefficients of 13.0 and 5.0 x 10(-7) m2 s(-1) were calculated from a methane diffusion assay for planted and unplanted soils respectively, indicating the positive effect of plant roots on gas diffusion into the soil. A second, modified column study removed 87, 73, 63, and 45% of PCB after 12 weeks in the 0 to 5, 5 to 11, 11 to 26, and 26 to 35 cm depths, respectively, in planted-bioaugmented soils, whereas 65, 54, 53, and 47% of PCB was removed from the planted-minimal salts treatment, respectively. Shifts in the soil microbial community structure were demonstrated by denaturing gradient gel electrophoresis of bacterial 16S ribosomal DNA. Results support that Brassica nigra directly contributed to accelerated PCB removal by increased oxygen diffusion, amendment infiltration, and microbial enrichment.

Biodegradation, Environmental↗

PubMed2002

Traffic patterns and childhood cancer incidence rates in California, United States.

OBJECTIVE: Some studies have suggested that residential proximity to high traffic areas is associated with increased risk of childhood cancer, although the epidemiologic evidence to date has been mixed. This study takes advantage of available information on population-based cancer reporting and various spatially assigned indices of traffic in a sufficiently large and heterogeneous area to obtain reasonably stable estimates of risk associations. METHODS: The time period 1988-1994 included a total of 7143 newly diagnosed cases of childhood cancer and 46 million child-years of observation in California. Rate ratios, estimated via Poisson regression (with adjustment for age, sex, and race/ethnicity), were computed for estimated traffic level as measured by spatial information on neighborhood vehicle density, road density, and traffic density. RESULTS: Compared to area air monitoring data, traffic density estimates were the most strongly correlated with measures of benzene and 1,3-butadiene. Rate ratios at the 90th percentile of traffic density (neighborhoods with over 320,700 vehicle miles traveled per day per square mile) were 1.08 (95% Cl 0.98-1.20) for all cancers in children, 1.15 (95% CI 0.97-1.37) for the leukemias, and 1.14 (95% CI 0.90-1.45) for the gliomas. There was also little or no evidence for rate differences in areas characterized by high vehicle or road density. CONCLUSION: These data suggest that childhood cancer rates are not higher in high traffic neighborhoods, but future studies which can better refine timing and measures of exposure are needed to more directly address the question of etiologic risks.

Adolescent↗

PubMed2002

Analysis of conditional mutations in the Saccharomyces cerevisiae MLH1 gene in mismatch repair and in meiotic crossing over.

In mismatch repair (MMR), members of the MLH gene family have been proposed to act as key molecular matchmakers to coordinate mismatch recognition with downstream repair functions that result in mispair excision. Two members of this gene family, MLH1 and MLH3, have also been implicated in meiotic crossing over. These diverse roles suggest that a mutational analysis of MLH genes could provide reagents required to identify interactions between gene products and to test whether the different roles ascribed to a subset of these genes can be separated. In this report we show that in Saccharomyces cerevisiae the mlh1Delta mutation confers inviability in pol3-01 strain backgrounds that are defective in the Poldelta proofreading exonuclease activity. This phenotype was exploited to identify four mlh1 alleles that each confer a temperature-sensitive phenotype for viability in pol3-01 strains. In three different mutator assays, strains bearing conditional mlh1 alleles displayed wild-type or nearly wild-type mutation rates at 26 degrees. At 35 degrees, these strains exhibited mutation rates that approached those observed in mlh1Delta mutants. The mutator phenotype exhibited in mlh1-I296S strains was partially suppressed at 35 degrees by EXO1 overexpression. The mlh1-F228S and -I296S mutations conferred a separation-of-function phenotype in meiosis; both mlh1-F228S and -I296S strains displayed strong defects in meiotic mismatch repair but showed nearly wild-type levels of crossing over, suggesting that the conditional mutations differentially affected MLH1 functions. These genetic studies suggest that the conditional mlh1 mutations can be used to separate the MMR and meiotic crossing-over functions of MLH1 and to identify interactions between MLH1 and downstream repair components.

Adaptor Proteins, Signal Transducing↗