Research2


 Postdoctoral Research
 Montana State University
 Department of Earth Science
 Bozeman, MT
 
2014-2015
  Many geochemical processes thought to be abiotic in nature are in fact regulated and enhanced by microbial activities. My research interests span a broad range of topics driven by the overarching objective to understand how aqueous geochemistry and microbe-mineral interactions drive chemical cycling between the hydro-, bio- and litho-spheres and contribute to system habitability. Investigations include both laboratory and field based studies that integrate molecular and geochemical analyses to identify environmentally relevant microbe-mineral interactions. Current laboratory based investigations include evaluating the ability of an alpine subglacial bacterial isolate to drive pyrite (FeS2) oxidation under aerobic and anaerobic conditions, and the importance of direct microbe-mineral contact for bioavailability of mineral-bound elements. Fieldwork included studying how geochemical parameters and mineralogy shape the endogenous microbiome at Robertson Glacier, Peter Loughleed Provincial Park, Alberta, Canada, and the Mount Rainier Summit Firn Caves, Washington, USA.  Developing an understanding of the microbe-mineral connections that contribute to the habitability of subglacial and glacio-volcanic environments will provide direction for the next astrobiological target in the search for life beyond Earth. 




Doctoral Research:
University of Washington
Department of Earth and Space Sciences
Seattle, WA
2008-2014
   As single celled organisms, bacteria rely on a high surface area to volume ratio to obtain compounds necessary for their metabolic processes. This geometric configuration maximizes the interface between microbial cell walls and the surrounding environment; promoting efficient chemical transfer into and out of the cell while also providing a highly reactive, complex organic surface in many environmental media. In effect, microbial surfaces are the interface between cellular and geochemical processes and thus represent a physical confluence of the bio-, hydro- and litho- spheres. My doctoral dissertation furthers our understanding of how and to what extent bacterial surface reactivity influences geochemical processes within the hydro- and lithospheres.

AGU 2013 Fall Meeting Poster: 
  


 
 
Geochemistry Field Assistant
Thule and Kangerlussuaq, Greenland
2011, 2012 Melt Seasons

 
I worked as a field assistant in Thule and Kangerlussuaq, Greenland, for a collaborative project designed to elucidate a link between sub-glacial microbes and their effect on chemical weathering rates.  My primary roles as a field assistant include collecting basal water samples and geochemical data such as water pH, oxygen content, temperature, alkalinity and iron content.  Field sampling and laboratory work was full of surprises and kept us on our toes! Check out my blog for some accounts of our adventures.

PIs: Dr. Karen Junge, Dr. Ron Sletten, Dr. Brent Christner, and Dr. Birgit Haagedorn



Post-Doctoral Research
Montana State University
Earth Science Department
Bozeman, MT
2014 - 2015

        Many geochemical processes thought to be abiotic in nature are in fact regulated and enhanced by microbial activities. My research interests span a broad range of topics driven by the overarching objective to understand how aqueous geochemistry and microbe-mineral interactions drive chemical cycling between the hydro-, bio- and litho-spheres and contribute to system habitability. Investigations include both laboratory and field based studies that integrate molecular and geochemical analyses to identify environmentally relevant microbe-mineral interactions. Current laboratory based investigations include evaluating the ability of an alpine subglacial bacterial isolate to drive pyrite (FeS2) oxidation under aerobic and anaerobic conditions, and the importance of direct microbe-mineral contact for bioavailability of mineral-bound elements. Fieldwork included studying how geochemical parameters and mineralogy shape the endogenous microbiome at Robertson Glacier, Peter Loughleed Provincial Park, Alberta, Canada, and the Mount Rainier Summit Firn Caves, Washington, USA.  Developing an understanding of the microbe-mineral connections that contribute to the habitability of subglacial and glacio-volcanic environments will provide direction for the next astrobiological target in the search for life beyond Earth.



Doctoral Research:
University of Washington
Earth and Space Science Dept.
 Seattle, WA 
2008-2014
        
        As single celled organisms, bacteria rely on a high surface area to volume ratio to obtain compounds necessary for their metabolic processes. This geometric configuration maximizes the interface between microbial cell walls and the surrounding environment; promoting efficient chemical transfer into and out of the cell while also providing a highly reactive, complex organic surface in many environmental media. In effect, microbial surfaces are the interface between cellular and geochemical processes and thus represent a physical confluence of the bio-, hydro- and litho- spheres. My doctoral dissertation furthers our understanding of how and to what extent bacterial surface reactivity influences geochemical processes within the hydro- and lithospheres.

        Thermodynamics of endospore adsorption - Bacterial surface adsorption has the capacity to affect metal speciation and transport in aqueous environments and may even serve as a precursor to cellular internalization. Extensive research on vegetative bacterial cell-surface adsorption has, however, largely overlooked the proteinaceous, bacterial endospore coat as a potentially effective adsorbent. My research employed simultaneous potentiometric titration and isothermal titration calorimetry (ITC) analyses to study the thermodynamics of Bacillus subtilis endospore-proton adsorption. This novel approach reveals a level of chemical complexity that is unresolvable by either individual data set. Data is modeled based on chemical thermodynamics using multi-site non-electrostatic surface complexation models (NE-SCM). Model derived adsorption sites provide insight into adsorption at the molecular level and suggest the presences of proton active organic acids on the endospore surface such as carboxyl, phosphate and thiol groups. NE-SCMs from my work also provide a framework for modeling endospore-metal adsorption in macro-scale systems. In 2009 I was awarded a NSF Graduate Research Fellowship based on this research. Results were published in 2013. 


       
Bacillus subtilis spore surface protonation and heat released as a function of pH 
(Harrold and Gorman-Lewis, 2013)


        Endospore-metal adsorption – Endospores, a physically robust and metabolically dormant cell type, have potential as biosorbents in the environment and for heavy metal remediation. To better evaluate endospore-metal adsorption capacity I quantified and modeled the adsorption behavior of uranium (U), cadmium (Cd), magnesium (Mg) and silica (Si) to the endospore surface as a function of solution pH, time, element:endospore ratio and in systems containing multiple metals. Favorable U, Cd and Mg-endospore adsorption suggests these reactions have the capacity to affect metal concentrations and associated chemical equilibriums in the environment. Negligible Si-endospore adsorption under all conditions studied suggests direct Si-bacteria adsorption has little to no effect on geochemical processes. NE-SCMs describing endospore-metal adsorption provide insight on the chemical identity of surface sites and serve as a robust predictive tool for quantifying endospore-metal adsorption in macro-scale systems. 


        The effect of microbial surface reactivity on mineral dissolution – Microbial surface reactivity has the capacity to alter aqueous chemical equilibrium and affect mineral dissolution rates. My research is the first to utilize endospores, a metabolically dormant cell type, as a tool and cell surface proxy to isolate and quantify the effect of microbial surface reactivity on long-term (40-80 d) mineral dissolution rate. This work demonstrates that both endospore ion adsorption and mineral adhesion increase forsterite (Mg2SiO4) dissolution rate, likely though endospore-Mg bonding, and can be described according to a compound rate law. Results provide clear evidence for a novel microbe-mineral interaction. Implications of these findings are two-fold: 1) bacterial surfaces affect mineral dissolution rate and aqueous geochemical processes, and 2) cell wall surface reactivity can facilitate the release of mineral bound nutrients and may have a function in chemolithoautotrophy. 


AGU 2013 Fall Meeting Poster: 

 


Greenland Field Assistant
Thule and Kangerlussuaq, Greenland




    In summer 2011 and 2012 I spent 7 weeks in Thule and Kangerlussuaq, Greenland, respectively, as a field assistant for a collaborative project designed to elucidate a link between sub-glacial microbes and their effect on chemical weathering rates.  My primary roles as a field assistant include collecting basal water samples and geochemical data such as water pH, oxygen content, temperature, alkalinity and iron content.  Field sampling and laboratory work was full of surprises and kept us on our toes!  Check out my blog for some accounts of our adventures.

PIs: Karen Junge, Ph.D., Ron Sletten, Ph.D., Brent Christner, Ph.D. and Birgit Haagedorn, Ph.D.