Associate Professor, Director Undergraduate Curriculum
Room 230 Environmental & Natural Resource Sciences Building
Primary research initiatives involve evaluating the properties of soil which define soil quality and assessing the capability of implementing soil remediation procedures to optimize the soil quality level. The overall objective of these studies is to derive principles applicable to assessment and management of industrially contaminated soil sites. The product of the optimized soil quality will be improvement of both ecosystem quality and overall environmental health. Specific research areas include:
Other research activities include study of a) the behavior of xenobiotics and native organic compounds in soil and their impact on ecosystem stability and b) biogeochemical cycles in native ecosystems and the factors controlling these processes. The studies of the behavior of xenobiotics in soils have involved the examination of reclamation and management practices for disturbed soils, behavior of antibiotics and various carcinogens in soils, and problems associated with disposal of radioactive wastes. Objectives of the biogeochemical cycle projects relate to the elucidation of the responsible microbial populations, determination of the enzymes involved in the mineralization reactions, evaluation of the rates of plant nutrient movement through various soil organic matter pools (including the effect of various management systems on this nutrient mobility), and delineation of plant-microbe interactions affecting nutrient cycles.
Abstract: For bacterial inoculants to be effective in soil remediation, the bacterial strain must be capable of overcoming any negative effects of soil minerals on cellular processes. One class of minerals commonly encountered by soil bacteria are clays. Thus, the effect of commonly occurring clay minerals in soils on starvation, survival and 2-hydroxypyridine catabolism by Arthrobacter crystallopoietes was evaluated. Stationary phase A. crystallopoietes cells were suspended in 0.03 M, pH 7.0, phosphate buffer containing no clay or amended with 0.2%(w/v) montmorillonite, sodium montmorillonite, or kaolinite. Marked effects of clay minerals on both survival rates and catabolic rates of 2-hydroxypyridine were noted. For example, after 14 weeks starvation, 4.6% of the initial cell population were viable with no clay present, compared to 0.8% (montmorillonite), 22.1% (kaolinite) and 54.1% (sodium montmorillonite) in the presence of the clay minerals. Acclimated and non-acclimated cell populations were used to evaluate 2-hydroxypyridine catabolism. Induction of 2-hydroxypyridine metabolism occurred in the unacclimated cells following starvation. Differential impact of the clay minerals on unacclimated cells was detected. Montmorillonite enhanced the capacity for induction of 2-hydroxypyridine catabolism and its decomposition rate after 0 to 3 days starvation. For acclimated cells, clay did not affect the metabolic activity prior to starvation, but the presence of clay resulted in increased activity during starvation. For example, after 3 days starvation, a nearly two fold increase in metabolism was detected in the presence of clay minerals. These data suggest that some clay minerals in soil alter the survival time and metabolic activity of soil amended bacteria, thereby affecting the potential for bioremediation success.
Abstract: Bacterial strains amended to soil to facilitate bioremediation of sites contaminated with organic substances must be capable of surviving and functioning in the presence of a variety of soil organic and mineral components. Thus, the influence of humic acid on 2-hydroxypyridine catabolism, retention of 2-hydroxypyridine catabolic activity by whole cells, and hydrophobicity of the Arthrobacter crystallopoietes cells was examined. Humic acid, added to the starvation medium of the arthrobacter cells, which had been acclimated to catabolize 2-hydroxypyridine, resulted in increased stability of this metabolic activity compared to that of comparable cells starved in the absence of humic acid. For example, after 7 days starvation, cells incubated in the presene of 0.1%(w/v) humic acid oxidized 2-hydroxypyridine at a rate of 54.9 (moles hour-1 compared to 14.6 (moles hour-1 in the absence of humic acid. Although after 1 day starvation 2.5-fold more 2-hydroxypyridine catabolizing activity was detected in the presence of humic acid than in its absence, this enzymatic activity declined to undetectable levels after 3 days starvation both with and without humic acid in the starvation medium. No effect of humic acid was noted on protein content of the cells. Hydrophocity of the cells was not affected by humic acid during the first 4 days of starvation but after 7 days humic acid lessened the reduction in this property. Thus, changes in cell protein content and hydrophobicity did not explain the effect of humic acid on 2-hydroxypyridine catabolism by starving Arthrobacter crystallopoietescells.