Hope Johnson


Photograph of Hope JohnsonMicrobiology of bacterial Mn(II) oxidation

Microbes play an important role in the global biogeochemical cycling of the elements. These cycles are vital for the health of the earth. We are specifically interested in the cycling of the transition element, Mn. Mn can exist in multiple redox states with the most prevalent in nature being Mn(II), Mn(III), and Mn(IV). Bacteria can catalyze both the oxidation and the reduction of Mn. We are interested in the oxidation of soluble Mn(II) to insoluble Mn(III,IV) oxides. Mn oxides are one of the most oxidative and reactive compounds in nature. As a result, Mn oxidizing bacteria can affect the biogeochemical cycles and fate of other compounds. They can oxidize other metals, pesticides, endocrine disruptors, and even prions. In addition, biogenic Mn oxides have a structural composition that enables them to adsorb other metals including lead and uranium. These properties of Mn oxides result in their potential for bioremediation.

Despite the importance of this group of bacteria to the cycling of Mn and other elements, very little is known on a molecular level about how and why these microbes perform this reaction. Our lab addresses the how and why of bacterial Mn oxidation.

Why do microbes oxidize Mn? Microbes may oxidize Mn to obtain energy, increase the bioavailable carbon, or to provide protection. We are using whole cell studies to quantitatively demonstrate protection provided by Mn oxides.

How do microbes oxidize Mn? Multiple enzymatic mechanisms may be employed by different phylogenetic lineages. We are investigating the properties of an animal heme peroxidase type enzyme present in alpha proteobacteria.

Selected publications

Anderson, C.R., Johnson, H.A., Caputo, N., Davis, R.E., Torpey, J.W., and Tebo, B.M. Localization and identification of a heme peroxidase adds complexity to the mechanism of Mn(II) oxidation in Aurantimonas manganoxydans strain SI85-9A1 and Erythrobacter sp. strain SD21. Applied and Environmental Microbiology 2009 75 4130-4138

Johnson, H.A., Hampton, E. and Lesley, S. A. The Thermotoga maritima Trk potassium transporter from frameshift to function. Journal of Bacteriology 2009 191: 2276-2284. 2009

Dick, G.J., Podell, S., Johnson, H.A., Rivera-Espinoza, Y., Bernier-Latmani, R., McCarthy, J.K., Torpey, J.W., Clement, B.G., Gaasterland, T., and Tebo, B. M. Genomic insights into Mn(II) oxidation by the marine a-proteobacterium Aurantimonas sp. strain SI85-9A1. Applied and Environmental Microbiology 2008 74 2646-2658

Johnson, H.A. and Tebo, B.M. In vitro studies indicate a quinone is involved in bacterial Mn(II) oxidation. Archives of Microbiology 2008 189 59-69

Tebo, B.M., Johnson, H.A., McCarthy, J. Templeton, A.S. Geomicrobiology of manganese(II) oxidation. Trends in Microbiology 2005 13 421-428