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.