Manganese (Mn) oxidizing microbes play an integral role in the global biogeochemical cycling of Mn by oxidizing soluble Mn(II) to insoluble Mn(III,IV) oxides. Beyond Mn, these microbes affect the fate of other metals, sulfur, and carbon and therefore can be used in bioremediation. The influence of these microbes beyond the Mn cycle is a result of the very reactive and adsorptive properties of biogenic Mn oxides formed by oxidation of Mn(II). Despite the important influence Mn(II) oxidizing microbes can have on biogeochemical cycles, we know very little on the cellular and molecular level about how and why microbes oxidize Mn(II). A new peroxidase enzyme was recently determined to oxidize Mn(II) in alpha proteobacteria. This new Mn(II) oxidizing enzyme raises questions about the process as well as how this unique enzyme may function. Understanding the mechanism of any type of Mn(II) oxidizing protein has been hindered by the extreme difficulty in obtaining purified Mn(II) oxidizing proteins from native sources. Therefore, this project will heterologously express this protein in Escherichia coli and characterize this new Mn(II) oxidizing protein. An understanding of this new enzyme will provide needed insight into the mechanism of Mn(II) oxidation and will expand our view of biochemical diversity and protein function. This project also investigates why bacteria oxidize Mn(II). The research will determine if Mn oxides provide cellular protection and affect intracellular manganese concentrations. Together, these studies will transform our view of Mn(II) oxidation as an important physiological as well as biogeochemical process.
Broader Impacts The Mn oxides produced by Mn(II) oxidizing bacteria can play an important role in bioremediation of metal and organic contaminated sites. Understanding how and why bacteria oxidize Mn(II) has the potential to better control this process, increasing its applicability. The research will be performed primarily by undergraduate research students. The students will work collaboratively and will be encouraged to publish and present their results at local and national meetings. These projects are excellent training opportunities for students in geomicrobiology, biochemistry, and biotechnology. The interdisciplinary training will yield students ready to succeed in the biotechnology industry, graduate school, or a health professional school. California State University is a Hispanic serving institution and training of underrepresented students will be an integral part of this project.
Microbial manganese (Mn) oxidation is an important process in the cycling of Mn and other elements on our planet. These bacteria produce Mn(III,IV) oxides which can react with and adsorb other elements. This also makes them a potential tool for cleaning up contaminated sites by bioremediation. Although we know this process is important for biogeochemical cycling, we do not understand the bacterial enzymes that catalyze this reaction or the reason why bacteria perform this reaction. This study made important progress toward understanding this process. When many bacteria produce Mn(III,IV) oxides, the cell becomes coated in this mineral, thus it could act as a type of armor for the cell. We found this armor can protect bacteria against hydrogen peroxide stress. Hydrogen peroxide is naturally occurring, but it can damage cells. Mn oxides help to prevent that damage. In addition, we found that cells that oxidize Mn also increase the amount of Mn inside the cell. This may indicate that Mn oxidation is involved in how bacterial cells control the amount of this metal inside of the cell. One reason we know so little about the enzymes that catalyze bacterial Mn oxidation is because they are present at very low levels. To overcome this quantity problem, we were able to produce relatively large quantities of a bacterial Mn oxidizing protein in E. coli. Preliminary studies indicate it is a very novel protein with a new type of mechanism. This project also helped to fund the laboratory and research training of 25 undergraduate, 5 Master’s students, high school teachers and high school students. More than half of the students were first generation college students or underrepresented in STEM.
