Microbes, Minerals, & Metals

The Geochemistry & Geobiology Laboratory investigates the geochemical imprint of microbial life on the Earth’s surface environment through geological time by studying modern microbial metabolisms and the behavior of metals and minerals under varying aqueous redox regimes. A major focus of our work is understanding the impact of ferruginous conditions on regulating microbial activity and biogeochemical cycling.

Current Projects

Refining the geochemical toolkit for paleoredox reconstruction: uranium isotope behavior under suboxic, anoxic, and iron-rich conditions.

This project seeks to validate uranium isotopes as a paleoredox proxy. Our part at ISU is investigating this proxy in modern ferruginous lakes.

PI: Stephen Romaniello (ASU)
Co-PI: Geoff Gilleaudeau (GMU), Elizabeth Swanner (ISU)
Funding: NASA Exobiology


Determining the mechanism(s) of sedimentary pyrite formation.

Pyrite (FeS2) is a ubiquitous mineral in anoxic marine sediments. Its formation is enigmatic as the initial mineral product of microbial sulfate reduction is S2-, yet the average oxidation state of sulfur in pyrite is S1-. This study therefore aims to determine what aqueous and solid sulfur species are present in sediments where pyrite is forming.

Voltammetric detection of sulfur species will be coupled to synchrotron-based sulfur XANES and XRF mapping, along with traditional bulk techniques such as acid-volatile sulfide (AVS). It is hoped that a better accounting of intermediates will give insight into pyrite formation pathways, as well as the role of sulfur-cycling microbes to this process in anoxic sediments.

People: Raisa Islam (MS student at ISU)
PI: Elizabeth Swanner
Funding: American Chemical Society Petroleum Research Fund, Doctoral New Investigator (DNI)

A systems approach for understanding, predicting, and managing harmful algal blooms in Midwestern lakes

Freshwater Harmful Algal Blooms (HABs) threaten the safety of recreational and drinking waters worldwide. Here in Iowa, our team will identify genetic markers for cyanotoxin production for development of PCR-based chips. These will be used to screen waters from Iowa’s lakes for HABs, in addition to using metadata on samples to determine the ecological and environmental drivers of HABs. A multi-wavelength fluorometer approach will also be applied to tracking blooms and identifying when toxin measurements are needed. Another suite of activities will involve cultivation of cyanotoxin-producing strains, as well as toxin-degrading bacteria from Iowa’s lakes. This systems approach will implement strategies for identifying and mitigating the effects of HABs in Iowa and regionally.

People: Tania Leung & Micah Fatka (PhD and MS students in Swanner group), Xuwei Liang (PhD in Ikuma group), and Jaejin Lee (postdoc in Howe group)
PI: Adina Howe, Kaoru Ikuma, Elizabeth Swanner and Jinlyung Choi
Funding: Environmental Protection Agency

Biosignatures of coupled iron and carbon cycling in ferruginous lakes

Prior to the evolution of oxygenic photosynthesis, anoxygenic photosynthetic bacteria may have utilized Fe(II) as an electron donor to fuel marine primary productivity. As the habitat for these microbes, “photoferrotrophs”, on the modern Earth requires Fe(II), no oxygen, and sunlight, we have identified two lakes in the midwest to study carbon cycling under ferruginous conditions. We use a combination of traditional limnology approaches, and seasonal monitoring, along with next-generation (meta)genomic sequencing techniques and culturing to study lakes where anoxygenic photosynthesis is a major pathway. Our field sites are Brownie Lake in MN, and Canyon Lake in the Upper Peninsula of MI.

People: Nick Lambrecht (Postdoc at ISU)
PI: Elizabeth D. Swanner
Collaborators: Chad Wittkop (MNSU-Mankato), Sergei Katsev & Cody Sheik (UM-Duluth)
Funding: National Science Foundation and Huron Mountain Wildlife Foundation

Past Projects


Earth analogues for sedimentary manganese enrichments observed in a Martian paleolake

Trace elements in sedimentary manganese minerals forming in redox-stratified lakes, oxic lakes, and ancient chemically stratified marine basins will be quantified and used to help interpret the manganese enrichments in Gale Crater on Mars. Gale Crater is interpreted to be a redox-stratified paleolake. Calibrations for laser induced breakdown spectroscopy (LIBS) data from the Curiosity Rover currently in Gale Crater will be developed and data compared to Earth samples.

People: Gabbie Ledesma (Undergraduate Geology major at ISU)
PI: Elizabeth Swanner
Collaborators: Nina Lanza (Los Alamos National Laboratory), Chad Wittkop (MNSU-Mankato)
Funding: Iowa Space Grant Consortium Early Career Investigator Research Program (ECIRP)

The role of iron mobility from anoxic sediments in stimulating harmful algal blooms

Harmful algal blooms (HAB) threaten the health and safety of Iowa’s surface waters, and are increasingly common. This project proposes to study if enhanced sedimentary sources of iron stimulate HABs. Work will involve geochemical and microbiological profiling of the water column, and measurement of sedimentary iron fluxes using microelectrodes.



People: Tania Leung (PhD student at ISU), Erin Atchison (Geology major at ISU)
PI: Elizabeth D. Swanner
Collaborators: Iowa Lakeside Laboratory Regents Resource Center
Funding: Iowa Water Center (USGS)

Funding sources