Steve Wilhelm

Keywords:

Molecular biology & physiology of aquatic prokaryotes, functional genomics in natural communities, marine & freshwater viruses, aquatic biogeochemistry, siderophores

Research Area:

Description of Research:

A. Development of Molecular Diagnostics for Iron Stress

Experimental evidence has demonstrated that Fe availability plays critical role in marine productivity. Work in the laboratory is currently attempting to develop molecular diagnostics that will provide for a biological indication of the iron status of the marine microbial community. Work in this area involves the development of novel PCR-based probing systems as well as the construction of bioluminescent bioreporter systems (with Drs. B. Applegate and G. Sayler) for use in field systems.

B. Regulation of Microcyctis Toxin Production and the Development of Molecular Diagnostics

In collaboration with Dr. R. Michael McKay (BGSU) and Dr. G. Boyer (SUNY-ESF) we are examining factors that influence toxin production and cellular proliferation of the harmful algal bloom cyanobacterium Microcystis. This work is a component of a multi-institutional, multi-national effort. It will provide insight on the reoccurrence of this Harmful Algal Bloom (HAB) species in Lake Erie, on the potential for toxin production in the lake, and on the role of bioavailable Fe in regulating this process. As Microcystis is problem that affects freshwater lakes and reservoirs on a global scale, it is of utmost interest to resolve these issues. Techniques involved include quantitative PCR for the analysis of toxic cyanobacterial communities as well as the analysis of shotgun libraries from natural communities.

Currently we are also developing genome wide approaches to examining factors that influence the physiology, toxicology and proliferation of Microcystis spp. in natural systems. In conjunction with Dr. Gary Stacey (UT Microbiology) we have recently obtained funding to construct and array a genomic DNA library from a toxic Microcystis sp., which we will then use in experiments to determine the influence of critical environmental parameters (e.g., nutrient availability) of gene expression. The long term goal of this study is to developed of microchip-based system to examine the "health" of aquatic systems.

We are also screening the natural viral community for lytic agents that may regulate Microcystis populations. Viral abundance is high in this (and other freshwater) systems and knowledge of the distribution of lytic agents is critical to understanding the ecology of this cyanobacterium.

C. Influence of Viruses on Marine Biogeochemical Cycles

Viruses are a major cause of prokaryotic mortality in aquatic systems, but in spite of suggestions that they are important in nutrient recycling, only minimal quantitative evaluations of this process exist. Preliminary data demonstrate that viruses can mediate rapid transfers of elements to bacteria and other plankton. As prokaryotic organisms represent the majority of the living biomass in the ocean, viral lysis of autotrophic and heterotrophic prokaryotes represents a little-studied source of potentially limiting nutrients to marine organisms.

The biological availability of Fe has been demonstrated to be major factor regulating pro-ductivity of marine plankton. Central to the problem of resolving marine Fe cycles has been a lack of understanding of the sources, sinks and recycling mechanisms for iron. Recent evidence suggests that the bioavailability of Fe to marine organisms is regulated by the complexation of Fe by uncharacterized organic ligands in seawater. While significant effort has been put forth to look at potential sources for these ligands (e.g., grazing byproducts, siderophore production by marine prokaryotes, etc.) there remains little work examining for virus-mediated cell lysis as a source of organic Fe com-plexes. We are measuring virus-mediated release of Fe and C from host cells using radioisotope and ultrafiltration techniques, and examine subsequent Fe bioavailability. Since many marine regions (including some iron-limited ones) are dominated by prokaryotic organisms, our studies focus on viruses that infect heterotrophic and phototrophic prokaryotes.

Field Research In 2000, students and research from our group will have visited many exciting locations, including the Sargasso Sea, the Northeast US seaboard, the Great Lakes, the Western Coast of South America, the Western Coast of Canada and Bering Sea, and the coastal upwelling zones of California, the Galapagos Islands and Peru.

Contact Information

Steve Wilhelm
Molecular Genetics and Systems Biology
Associate Professor, Department of Microbiology

UT
633B Science and Engineering Research Facility
University of Tennessee
Knoxville, TN 37996

Email: wilhelm@utk.edu

Degrees