Characterization of Metal-Precipitating Proteins From Marine Bacterial SporesEPA Grant Number: U914780
Title: Characterization of Metal-Precipitating Proteins From Marine Bacterial Spores
Investigators: Francis, Christopher A.
Institution: University of California - San Diego
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 1995 through January 1, 1996
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1995) Recipients Lists
Research Category: Fellowship - Bioremediation , Hazardous Waste/Remediation , Academic Fellowships
The overall objective of this research project is to investigate the potential metal removal applications of a marine bacterium that can detoxify metal ions via binding and oxidative precipitation.
Background: Metal pollution is a widespread problem in the marine environment. As a result, there is an increasing need for new technologies for remediating and preventing heavy metal pollution. The ultimate solution to metal pollution requires physically separating the metals from the environment. Microbially enhanced metal precipitation and recovery by high gradient magnetic separation is a promising technology for environmental bioremediation.
Metal pollution poses a serious threat to a variety of terrestrial and marine ecosystems. One problem of recent concern to many coastal states is the presence of metal-contaminated sediments, especially in estuaries and bays bordered by industrial activity. These sediments are a constant source of metals into the overlying water, a problem which is magnified when they are disturbed due to natural or anthropogenic causes such as storm events or dredging activities. Unfortunately, there are very few satisfactory solutions to metal pollution problems. Bioremediation, the use of naturally occurring or genetically engineered microorganisms to degrade or detoxify pollutants, is one of the most promising approaches for environmental cleanup. Many studies have focused on the microbial degradation of organic xenobiotics into less harmful compounds, but metal pollutants pose a more difficult problem because they cannot be degraded. Instead, metals may undergo transformations that alter the chemical speciation, species concentration, oxidation state, or form of the metal, with metal ions being the most toxic. Thus, microorganisms that catalyze metal transformations influence both the toxicity and mobility of metals in the environment.
Under aerobic conditions, manganese (Mn) oxidation is a thermodynamically favorable but kinetically slow process that results in the transformation of dissolved Mn(II) to particulate Mn(III,IV) oxides or oxyhydroxides, mineral phases that adsorb and oxidize many other metals and organic compounds. The marine Bacillus sp. Strain SG-1 was originally isolated as a manganese-oxidizing bacterium. SG-1 produces spores that have a number of features that make them potentially useful for metal bioremediation. These dormant spores not only bind and oxidize manganese, cobalt, and iron, but also bind a variety of other heavy metals such as cadmium, zinc, and nickel. Thus, SG-1 may have applications for dealing with mixtures of metals, which is a common problem. SG-1 is capable of binding or oxidizing metals both directly on the spore surface or through the adsorption or oxidation on the Mn oxides that accumulate on the spore surface. SG-1 spores are active over a wide range of environmental conditions, such as salinity (freshwater and seawater), pH (>6), temperature (2-80°C), and metal concentrations (<nM to > mM) (Lee and Tebo, 1994). The rates of Mn(II) oxidation at neutral pH are more than five orders of magnitude faster than would occur by chemical mechanisms (Hastings and Emerson, 1986). Spores are naturally resistant to physical and chemical agents or stresses, and can accumulate Mn oxides over five times their cell weight. Most importantly, SG-1 spores can oxidize Mn even when rendered non-germinable, allaying concerns over the release of living or genetically engineered organisms into the environment.