Shewanella Federation

Why study the bacterium Shewanella oneidensis strain MR-1?

Similar to a human breathing in oxygen and exhaling carbon dioxide, Shewanella has the ability to 'inhale' certain metals and compounds and 'exhale' these metals in an altered state. For example, Shewanella can convert uranium dissolved in contaminated groundwater to a form incapable of dissolving in water, preventing uranium from spreading as the groundwater flows. This ability makes Shewanella an important factor in confining and cleaning up contaminated areas—areas such as DOE sites contaminated during the manufacture of nuclear weapons.

Shewanella has several other characteristics that make it well suited for use in environmental clean up. It can grow naturally almost anywhere, and does not cause disease in humans or other organisms. These properties make it an ideal bacterium for bioremediation of contaminated environments, while reducing the risk of harmful side effects often associated with traditional methods of site cleanup.

In the laboratory, Shewanella has advantages that make it easier for researchers to study. Shewanella is related to Escherichia, a bacterium well known to microbiologists. Tools and techniques developed over the past 30 years for Escherichia work with Shewanella. Shewanella also has the ability to tolerate oxygen—a useful ability that makes it easier to work with in the laboratory and is missing in other groups of metal metabolizing bacteria.

Bioremediation potential...
Shewanella oneidensis strain MR-1 is a metabolically versatile bacterium that can use a diversity of organic compounds and metals to obtain energy needed for growth and survival. Many of the compounds and metals that Shewanella can use for energy and growth—iron, uranium, manganese, sulfur, and nitrates—are toxic to humans and other organisms when concentrated in the environment. Growth of Shewanella alters the ionic properties (electronic charge) of metals, which affects their solubility and the solubility of other potentially harmful chemicals in their proximity.

The solubility of a metal or compound controls the speed in which it moves through the environment—an important factor when considering the bioremediation of a contaminated site. Sites containing a mixture of these and other harmful metals include Department of Energy sites contaminated during the manufacture of nuclear weapons. A confounding factor is that soils and sediments containing high concentrations of these metals are often devoid of oxygen. Fortunately Shewanella has evolved the ability to grow and thrive on metals in the absence of oxygen while retaining the ability to tolerate oxygen during growth on other compounds. These physiological properties present Shewanella as a potential biological solution to remediate contaminated DOE sites in a directed and efficient manner.

Researchers participating in the DOE-funded Shewanella Federation will use a suite of complementary approaches to model the biology of Shewanella at the whole-genome level to predict how this bacterium will respond to different environment conditions. An understanding of these responses to the environment will direct efforts to biologically remediate contaminated sites of diverse composition.

A model biological system for understanding metal reduction...
The diverse metabolic and physiological capabilities of Shewanella also make it a good organism for laboratory study. Shewanella oneidensis MR-1 is a Gram negative bacterium related to the microbiologists' "lab-rat", Escherichia coli. Many of the laboratory tools developed over the past 30 years to manipulate the genetic code of Escherichia coli, also work in Shewanella. In addition, the ability of Shewanella to tolerate oxygen allows researchers to perform genetic manipulations without specialized, and cumbersome, equipment for excluding oxygen.

The ability to grow both in presence and absence of oxygen is important since growth on metals can only occur in the absence of oxygen. Researchers can alter genes involved in growth on metals under normal laboratory conditions (oxygen present), and then grow Shewanella in the absence of oxygen to understand the effects of these genetic alterations on metal growth processes. Genetic tools developed for E.coli and the whole-genome sequence (completed in 2001 under a separate DOE-funded genome sequence project) will permit researchers to individually study each of the approximately 5000 genes that comprise the entire genetic sequence of Shewanella.

	*Why study the bacterium Shewanella oneidensis* strain MR-1?** Similar to a human breathing in oxygen and exhaling carbon dioxide, Shewanella has the ability to 'inhale' certain metals and compounds and 'exhale' these metals in an altered state. For example, Shewanella can convert uranium dissolved in contaminated groundwater to a form incapable of dissolving in water, preventing uranium from spreading as the groundwater flows. This ability makes Shewanella an important factor in confining and cleaning up contaminated areas—areas such as DOE sites contaminated during the manufacture of nuclear weapons. Shewanella has several other characteristics that make it well suited for use in environmental clean up. It can grow naturally almost anywhere, and does not cause disease in humans or other organisms. These properties make it an ideal bacterium for bioremediation of contaminated environments, while reducing the risk of harmful side effects often associated with traditional methods of site cleanup. In the laboratory, Shewanella has advantages that make it easier for researchers to study. Shewanella is related to Escherichia, a bacterium well known to microbiologists. Tools and techniques developed over the past 30 years for Escherichia work with Shewanella. Shewanella also has the ability to tolerate oxygen—a useful ability that makes it easier to work with in the laboratory and is missing in other groups of metal metabolizing bacteria. Bioremediation potential... Shewanella oneidensis strain MR-1 is a metabolically versatile bacterium that can use a diversity of organic compounds and metals to obtain energy needed for growth and survival. Many of the compounds and metals that Shewanella can use for energy and growth—iron, uranium, manganese, sulfur, and nitrates—are toxic to humans and other organisms when concentrated in the environment. Growth of Shewanella alters the ionic properties (electronic charge) of metals, which affects their solubility and the solubility of other potentially harmful chemicals in their proximity. The solubility of a metal or compound controls the speed in which it moves through the environment—an important factor when considering the bioremediation of a contaminated site. Sites containing a mixture of these and other harmful metals include Department of Energy sites contaminated during the manufacture of nuclear weapons. A confounding factor is that soils and sediments containing high concentrations of these metals are often devoid of oxygen. Fortunately Shewanella has evolved the ability to grow and thrive on metals in the absence of oxygen while retaining the ability to tolerate oxygen during growth on other compounds. These physiological properties present Shewanella as a potential biological solution to remediate contaminated DOE sites in a directed and efficient manner. Researchers participating in the DOE-funded Shewanella Federation will use a suite of complementary approaches to model the biology of Shewanella at the whole-genome level to predict how this bacterium will respond to different environment conditions. An understanding of these responses to the environment will direct efforts to biologically remediate contaminated sites of diverse composition. A model biological system for understanding metal reduction... The diverse metabolic and physiological capabilities of Shewanella also make it a good organism for laboratory study. Shewanella oneidensis MR-1 is a Gram negative bacterium related to the microbiologists' "lab-rat", Escherichia coli. Many of the laboratory tools developed over the past 30 years to manipulate the genetic code of Escherichia coli, also work in Shewanella. In addition, the ability of Shewanella to tolerate oxygen allows researchers to perform genetic manipulations without specialized, and cumbersome, equipment for excluding oxygen. The ability to grow both in presence and absence of oxygen is important since growth on metals can only occur in the absence of oxygen. Researchers can alter genes involved in growth on metals under normal laboratory conditions (oxygen present), and then grow Shewanella in the absence of oxygen to understand the effects of these genetic alterations on metal growth processes. Genetic tools developed for E.coli and the whole-genome sequence (completed in 2001 under a separate DOE-funded genome sequence project) will permit researchers to individually study each of the approximately 5000 genes that comprise the entire genetic sequence of Shewanella.

© Michigan State University 2003