People | Clara Chan

• B.S., Geological and Environmental Sciences, Stanford University, 1997.
• M.S., Civil and Environmental Engineering, Stanford University, 1998.
• Ph.D., Earth and Planetary Science, University of California, Berkeley, 2006.

I study geomicrobiology, in particular the interactions between microbes and minerals. My research focuses on microbial mineralization, including  characterizing mineral phase, morphology, and reactivity, as well as investigating the roles microbes play in precipitation and crystallization processes. I take a multidisciplinary approach, combining geochemical field characterization and sampling, molecular biology, biochemistry, culturing and a wide variety of microscopy and spectroscopy techniques.

Biomineralization of neutrophilic Fe-oxidizing microbes
I have been studying the mineralogy and morphology of aerobic neutrophilic Fe-oxidizing microbes in both environmental samples and in culture. Many of these microbes create long, filamentous structures made of iron oxyhydroxides and organics. A well-known example is the twisted ribbon-like stalk of Gallionella ferruginea; A lesser-known example is a very similar stalk produced by Mariprofundus ferroxydans. How and why do these microbes produce mineralized stalks? Why do two different organisms (one terrestrial, and the other marine) create a morphologically similar stalk, and what does this tell us about the function of the stalk in the iron-oxidation metabolism? Fe-rich filamentous morphologies have been observed in the rock record, and interpreted as ancient Fe-oxidizing microbes. One of our goals is to connect details of morphology to physiological functions in order to establish biogenicity criteria for (putative) Fe microfossils. In collaboration with David Emerson (Bigelow Laboratory for Ocean Sciences), we have been observing biomineralization processes using time-lapse light microscopy imaging of microslide cultures. In this way, we are able to document mineralization patterns in gradient environments that mimic natural ones.

Cell surface structure and chemistry
Although microbes are often observed to accumulate metals on cell surfaces, many cells successfully escape encrustation, even in environments with high rates of both chemical and biologically-induced mineral precipitation. In collaboration with Luis Comolli and Birgit Luef (Lawrence Berkeley National Lab), we are using cryo-transmission electron microscopy and tomography to document cell surface structures and cell-mineral spatial relationships in minimally processed (cryo-fixed) samples of Gallionella and Mariprofundus cultures.

(More research details a

Sean Krepski, MS student

I am looking for graduate students and postdoctoral researchers. Please contact me if you are interested!

GEOL 467/667-010 Geomicrobiology (Fall 2009)