Lee R. Krumholz

Assistant Professor, Environmental Microbiology


Over the last several years, my research has focused on the study of microorganisms and environmentally relevant microbial processes occuring in oxygen depleted (anaerobic) environments. Most experiments have utilized microorganisms from subsurface (aquifer) sediments but others have included bacteria from freshwater and marine sediments. These studies have focused both on ecological processes , that is, the interactions of microorganisms and their surrounding ecosystem and on the potential of these microorganisms to carry out bioremediation processes. Dr. Krumholz The approach has taken several angles, with molecular studies, pure culture physiological and biochemical studies as well as studies with intact sediments. This breadth has allowed us to address questions ranging from very basic to very applied. Three projects are described in more detail below.

Physiology of Sulfate Reducing Bacteria

In this project, we have a considerable ongoing effort. This work will identify genes and ultimately physiological activities that are expressed under in situ conditions and are critical to function of sediment dwelling anaerobic bacteria especially as they live and grow in contaminated sediments. Our hypothesis is that sediment dwelling microorganisms have unique functions, encoded at the genetic level that are manifest only during exposure to conditions in contaminated environments. Further, these activities are missed using traditional in vitro laboratory incubations.

We are identifying genes of sulfate reducing bacteria (SRB) whose expression is necessary for the survival and activity of these organisms in contaminated environments. This involves the extrapolation of a molecular approach that has already proven successful for identifying genes expressed by pathogens only when these organisms are growing in a suitable host (in situ) and not when the organisms are in culture. Our approach takes on an ecological perspective. Which genes are expressed by sulfate reducers when they are exposed to and/or degrading a myriad of contaminants in sedimentary systems as opposed to those genes that may be expressed in laboratory cultures?

Subsurface Rock Ecology

Microbial processes in sandstones
Figure Legend. Drawing of the microbial processes occuring within sandstones at the interface of Cretaceous sandstones and shales.
This project has involved the study of sulfate reduction in consolidated rock material from a Cretaceous formation (100 million years before present) in central New Mexico. The goal of the study was to determine what factors enable sulfate reducing microbial communities to persist in subsurface rock formations. Sulfate reduction has been measured with both an assay using ground rock material as well as an in-situ assay using intact rock incubated with a silver foil to trap labeled sulfide. This latter protocol allows a two dimensional visualization of the location of sulfate reducing microorganisms. Both of these assays have demonstrated that the majority of the sulfate reduction observed in subsurface samples occurs at sandstone-shale interfaces. Through experiments, we have demonstrated that the mechanism for the maintenance of these communities is through the diffusion of nutrients from organic rich shales into sandstones. These sandstones provide a physical setting that is conducible to microbial growth. Work is continuing in this area.

Metal bioremediation

We have begun to study the detoxification of metals by sulfate reducing microbial communities in the subsurface. Heavy metals and radionuclides are often found as contaminants in subsurface locations. They are especially prevalent at Dept. of Energy sites where work on nuclear weapons and nuclear energy took place. Sulfate reducing bacteria produce sulfide which reacts with many metals to form insoluble precipitates. During the process, metals become concentrated in precipitates and are simply no longer found in the groundwater.

We are focusing on determining optimal conditions for these processes to occur in the subsurface.

Selected Publications:

For more information about this program, contact the Department or Dr. Lee Krumholz.


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