Hope A. Johnson, Ph.D., Stanford University
Assistant Professor of Biology
Personal Web Site: Coming Soon
Research Interests: Environmental Microbiology
Bacteria can take advantage of the redox properties of many metals and use them as a source or sink for electrons. In fact, some bacteria can breathe with metals just as we breathe with oxygen. Bacteria also require trace amounts of metals for many of their enzymes, yet metals in high amounts can be toxic. Therefore, bacteria have evolved many ways to control the level of metals within the cell. We are specifically interested in bacteria that oxidize the transition metal manganese. In the case of manganese, we do not fully understand how or why bacteria oxidize this metal and that is the focus of our research. Techniques in microbial physiology, molecular biology, and biochemistry will be used to approach this problem. An understanding of how bacteria oxidize manganese will not only give us insight into the striking diversity of microbial life but can also give us important tools for bioremediation.
Cyanobacteria can form macroscopic structures such as cones and stromatolites. Cone structures containing filamentous cyanobacteria may form on the surface of modern microbial mats at hot springs. Our lab is interested in understanding how these cone structures form by employing techniques in molecular biology, microbial physiology, and microbial ecology. Understanding this modern process may provide a window into how similar structures formed on early Earth.
Surface orientation affects the direction of cone growth by Leptolyngbya sp. strain C1, a likely architect of coniform structures in Octopus Spring (Yellowstone National Park). Reyes, K., Gonzalez, N.I, Stewart, J., Ospino, F., Nguyen, D., Cho, D.T., Ghahremani, N., Spear, J.R., and Johnson, H.A. Applied and Environmental Microbiology 79(4): 1302-8. 2013.
Anderson, C.R., Johnson, H.A., Caputo, N., Davis, R.E., Torpey, J.W., and Tebo, B.M. Mn(II) oxidation is catalyzed by heme peroxidases in "Aurantimonas manganoxydans" strain SI85-9A1 and Erythrobacter sp. strain SD-21. Applied and Environmental Microbiology 75(12): 4130-8. 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 alpha-proteobacterium Aurantimonas sp. strain SI85-9A1. Applied and Environmental Microbiology 74: 2646-58. 2008.
Johnson, H.A. and Tebo, B.M. In vitro studies indicate a quinone is involved in bacterial Mn(II) oxidation. Archives of Microbiology 189: 59-69. 2008.