Environmental Sciences Division

Selected Recent Abstracts in Microbial Genomics and Ecology by Anthony V. Palumbo

Contents 

1.0 U Reduction and Subsurface Microbiology

2.0 Carbon Sequestration

1.0 U Reduction and Subsurface Microbiology

1.1  Substrate and Community Structure Determinants of Uranium Reduction Rates in Subsurface Sediments. 3rd European Bioremediation Conference

Anthony V. Palumbo, Susan. M. Pfiffner, Lisa A. Fagan, Meghan S. McNeilly, Susan E. Rishell,  Chris W. Schadt, Jack C. Schryver, Jana R. Tarver, Joel E. Kostka, and Craig C. Brandt.

The goal of this work is to provide an improved understanding of the relationships between microbial community structure, geochemistry, and metal reduction rates in subsurface sediments. We are using microcosms containing slurries of sediment and groundwater from a high nitrate site to compare the effects of manipulations that influence community composition (different electron donors) on the rates of reduction of uranium(VI) to uranium(IV). In two experiments we observed nitrate reduction in microcosms treated with different electron donors (glucose, methanol, and ethanol) but not in controls. The rates of nitrate reduction appear to be higher with ethanol and glucose than with methanol. Ethanol and glucose promoted uranium reduction but methanol did not in either experiment. Effects of additional electron donors and changes in microbial community structure are being examined.

1.2 Effects of Electron Donor Additions on Uranium Reduction Rates in Subsurface Sediments. Abstract for the International Symposia for Subsurface Microbiology

Craig C. Brandt, Susan. M. Pfiffner, Lisa Fagan, Christopher Schadt, Meghan McNeilly, Susan Rishell, Joel E. Kostka, and Anthony V. Palumbo.

Background: Our goal is to improve our understanding of the relationships between microbial community structure, geochemistry, and metal reduction rates in subsurface sediments. Many microorganisms can change the geochemical conditions of subsurface sediments (e.g., cause a drop in redox) so metal reduction becomes an energetically favored reaction. The importance of microbial community composition on metal reduction rates may be minimal in such cases. However, some microbes can directly catalyze the necessary reactions so that metal reduction occurs more rapidly than without microbial activity. In this case, the composition of the community may be important if reduction is catalyzed by specific microorganisms.

Methods: We are using microcosms containing slurries of sediment and groundwater to compare the effects of manipulations that influence community composition (different electron donors) on the rates of reduction of uranium(VI) to uranium(IV). The sediments and groundwater, obtained from the U.S. Department of Energy’s NABIR Field Research Center, exhibit moderate levels of uranium, high nitrate concentrations and low pH. Replicated treatments of methanol, ethanol and glucose, together with a control (no substrate), were initiated and sampled weekly. The amounts of substrate added were chosen to equalize the electron transfer potential in each treatment.

Results: Metabolic activity was evident in all treatments after 2 weeks, and nitrate was depleted in all electron donors by week 4. Uranium concentration decreased significantly by day 29 in the ethanol treatment but had not significantly decreased by day 49 in the other treatments. Additional measurements will be made to determine if the decrease in uranium is due to a difference in lag time (e.g., different initial populations capable of using the substrate) or differences in community structure resulting from the different substrate additions.

Conclusions: The results suggest that the onset of uranium reduction is influenced by electron donor. Additional experiments are underway that use six electron donors run at several pH levels. Community composition will be characterized using several molecular methods, and non-linear data analysis methods will be used to related community composition to uranium reduction rates.

2.0 Carbon Sequestration

Anthony V. Palumbo, Jana C. Tarver, Lisa Fagan, Rose Ruther, and James E. Amonette

Previous work with leaching of metals from several fly ashes (both class F and class C) indicated minimal potential of leaching of toxic levels of metals from most fly ashes tested. Also, mixing fly ash with soil and other amendments (phosphate fertilizer) significantly decreases Cr, Li, Pb, and Cd in the leachate. One concern is that the characteristics of fly ash may be changed by the addition of NOx removal equipment that potentially results in higher levels of ammonia in the fly ash. We are concerned with fly ash since our laboratory and field studies show that addition of fly ash may increase carbon sequestration in reclaimed mine soils. However, the use of such amendments must overcome public concerns about possible release of toxic metals before the practice is generally accepted. We have recently been testing fly ash with a wide range of pH (3.7-12.4) originating from systems with NOx removal equipment. Toxicity testing with the Microtox© system has indicated little potential toxicity in leachates from the fly ash sources except for the fly ash at 12.4 pH. However, when the leachate from this fly ash was neutralized toxicity was eliminated. Additional data on ammonia and metal concentrations actually present in the fly ash should help indicate potential sources of toxicity (if any) and variations among the fly ashes.