RESEARCH INTERESTS

My research is in the area of geomicrobiology and centers on understanding the physiology that occurs at the interface between cells and inorganic surfaces. Understanding these interactions will help us understand the geologic history of the planet, how microbes and the Earth have "co-evolved" and the potential for using biominerals as tools for life detection. This understanding will also help in efforts to use bacteria for bioremediation, in efforts to understand and control corrosion and in efforts to use bacteria for energy production and materials processing.

Microbe-surface interactions
Bacteria are recognized as being significant to the breakdown and weathering of solids. Breakdown and dissolution rates are impacted by bacterial adhesion, the formation of biofilms and the release of metabolites. There is currently little quantitative data concerning the relationship between surface properties, bacterial adhesion, and biofilm formation. Understanding these relationships will provide greater insight into how microbes impact processes such as corrosion, nutrient cycling, bacterially-mediated degenerative diseases and indwelling device infections. My work in this area currently involves collaborating in the development of novel technologies that enable non-destructive observation of microbes on mineral surfaces, at multiple spatial scales and provide new quantitative insights in microbe-surface interactions.

Vertical scanning interferometry (VSI) is a non-contact, near in situ optical technique that can be used to image surface morphologies at nanometer-scale vertical resolution and submicron-scale horizontal resolution. Deep UV native fluorescence is a near real-time imaging method that utilizes deep UV radiation (<250nm) to detect and characterize bacterial cells on opaque surfaces without the need for tagging or altering the sample. These technologies will allow us to observe the chemical changes in a biofilm community as it interacts with mineral substrates, and to more accurately quantify the impact that bacterial metabolism and biofilm formation have on mineral dissolution kinetics.

Biogeochemistry
Iron biogeochemical cycling. Iron is one of the most important elements in soil biogeochemistry. Iron oxide minerals are good sorbents of pollutants such as arsenic, chromium, lead, and uranium. Any changes in the state of iron oxides in soils will impact the mobility of pollutants in groundwater. Traditionally, it has been thought that microbes had no impact on the nature of reduced iron minerals formed, other than to act as sources of ferrous iron. However, results from my dissertation indicate that microbes do influence the nature of reduced iron minerals. Although the exact nature of this influence remains to be elucidated, there may be interactions at the microbe-mineral interface that create microenvironments conducive to the formation of specific mineral products. A further understanding of the processes happening at this interface will provide us with greater insight into the role of microbial life in contaminated subsurface environments, and may provide us with the knowledge to make better use of microbes for remediation purposes.

Nanomaterials Processing. While materials like graphene and graphene oxide hold promise for various energy related endeavors, there is little information concerning the environmental impact of large-scale production. Recently, we have discovered that bacteria from the genus Shewanella have the ability to convert graphene oxides into graphene via respiration. The ability of microbes to process graphene oxides may provide a means of mitigating potential issues arising from their introduction into environmental systems. It also provides an opportunity for understanding the way microbes interact with graphitic substances.

Aqueous biochemistry. The combination of Deep UV native fluorescence and multivariate analysis allows for the classification of bacterial cells, spores and a wide range of organic compounds without the need for tagging or processing of the sample. This technology provides us with the potential to distinguish microbes in different physiologic states and of different pathogenic quality, based on protein expression, and to identify organic contaminants using a rapid, non-contact method. Presently, we are developing portable systems for use in the field, as well as laboratory systems that allow for real-time sample imaging.

Microbial fuel cells
There are a variety of bacteria capable of using solid surfaces as the terminal electron acceptor in their respiratory pathway. The capability to transfer electrons directly onto a solid surface has fostered the emergence of microbial fuel cells (MFCs). These devices are able to generate electrical current via the oxidation of organic carbon by bacteria. The promise of this nascent technology is the possibility of utilizing microbial respiration for bioenergy production and wastewater treatment. My research indicates that the electrode surfaces undergo corrosion during operation and that bacteria may mediate this process. Understanding the extent to which bacteria mediate this degradation will allow us to improve fuel cell lifetimes and overall performance.