Research

My research program focuses broadly on microbe:mineral interactions and the geological and ecological implications of these interactions in subsurface environments. My program currently has three separate but interrelated thrusts--microbial attachment to mineral surfaces; nutrient-driven microbial silicate weathering, and low temperature-dolomite precipitation. You will find pdf files of the references on the download page.

The role of mineral composition in microbial attachment to silicates
We find that mineralogic heterogeneity on the microscale can impact where microorganisms attach and colonize. Microbial attachment is a fundamental process in initiating a cascade of metabolic and weathering reactions and is also a potential means of sequestering pathogenic organisms in groundwater systems. We are currently investigating the role of silicate composition in microbial attachment.

Roberts, J.A., Fowle, D.A., Hughes, B.T., and Kulczycki, E. (2006) Attachment behavior of Shewanella putrefaciens to magnetite under aerobic and anaerobic conditions. Geomicrobiology Journal, 23, 631-640.

Roberts, J.A. (2004) Inhibition and enhancement of microbial surface colonization: the role of silicate composition, Chemical Geology, 212, 313-327.

Roberts, J.A., Hughes, B.T., and Fowle, D.A. (2004) Micro-scale mineralogic controls on microbial attachment to silicate surfaces: iron and phosphate mineral inclusions. Wanty, R.B. and Seal, R.R., eds. Water-Rock Interaction. Proceedings of the Eleventh International Symposium on Water-Rock Interaction WRI-11, Saratoga Springs, NY, USA 27 June – 2 July, v. 2, p. 1149-1153.

Fowle, D.A., Kulczycki, E., and Roberts, J.A. (2004) Linking bacteria-metal interactions to mineral attachment: A role for outer sphere complexation of cations? Wanty, R.B. and Seal, R.R., eds. Water-Rock Interaction. Proceedings of the Eleventh International Symposium on Water-Rock Interaction WRI-11, Saratoga Springs, NY, USA 27 June – 2 July, v. 2, p. 1113-1117.

Minerals as microbial habitats
The second research area investigates the interaction between mineral composition, mineral weathering, and microbial biodiversity in a variety of shallow groundwater ecosystems, including soils (Barro Colorado Island, Panama http://www.stri.org/), aquifers (USGS Toxic Substances Site http://mn.water.usgs.gov/bemidji/), and wetlands (Lost River Bog http://www.dnr.state.mn.us/snas/sna02003/index.html). My broad guiding hypothesis is that composition of the mineral phase controls weathering reactions by releasing either essential nutrients or toxic metals and these processes may serve as positive or negative feedbacks to weathering but may also influence the biodiversity and population succession of the surface colonizing microbial population.

Adamski, J.C., Roberts, J.A., and Goldstein, R.H. (2006) Entrapment of bacteria in fluid inclusions in laboratory-grown halite, Astrobiology, 4, 552-562.

Bennett, P.C., Engel, A.S., and Roberts, J.A. (2006) Counting and imaging bacteria on mineral surfaces: In Methods of Investigating Microbial-Mineral Interactions, CMS Workshop Lectures, Vol. 14, J. P.A. Maurice and L.A. Warren eds., The Clay Mineral Society, Chantilly, VA, 37-78.

Roberts Rogers, J. and Bennett, P.C. (2004) Mineral stimulation of subsurface microorganisms: release of limiting nutrients from silicates. Chemical Geology, 203, 91-108.


Low-temperature dolomite precipitation by methanogens
The third area of research is a recent expansion into the area of biomineralization. In particular, I am investigating the role of methanogenic microbial metabolism and cell wall structure on the nucleation and precipitation of ordered dolomite at low temperature. I have been successful at precipitating ordered dolomite in the laboratory in methanogenic, dilute groundwater at conditions that are near equilibrium with respect to dolomite and at Mg:Ca ratios <1. These results bring us one step closer to understanding this notoriously difficult mineral and we continue to pursue this area of research in both the laboratory and the field.

Roberts, J.A., Bennett, P.C., Macpherson, G.L., González, L.A., and Milliken, K.L. (2004) Microbial precipitation of dolomite in groundwater: Field and laboratory experiments. Geology, 32 (4) 277-280.