White Paper Title: 
Modeling the rates and constraints of hyperthermophilic Fe(III) oxide reduction

Tzi-Hsuan Jennifer Lin
Department of Microbiology, University of Massachusetts, Amherst, MA 01003

I am interested in biogeochemical processes in deep-sea hydrothermal systems and can contribute to the integration and synthesis of ideas related to in situ bioenergetics and habitat modeling as well as interactions between life and minerals. The study of hydrothermal vents has led to the discovery of novel hyperthermophile-mineral interactions that influence the biogeochemistry of their environment. Basalt-hosted, mildly reduced and mildly acidic hydrothermal systems appear to be ideal habitats for iron respiring microbes. Our studies have analyzed sulfide samples from the Endeavour Segment and Axial Volcano on the Juan de Fuca Ridge and found that iron reducers are the most abundant hyperthermophilic autotrophs in most samples (Ver Eecke et al., 2009; in preparation). Our pure culture mineral transformation studies show that these organisms oxidize H2 and reduce ferrihydrite (Fe(OH)3) to magnetite (Fe3O4) possibly with a maghemite (Fe2O3) intermediate. By studying the physiology of hyperthermophilic iron reducers and the physical nature of their mineral interactions and transformations, we can begin to model where these organisms are found in the subseafloor and the magnitude of their contributions to biogeochemical processes such as CO2 fixation and mineral alterations.

Modeling the in situ bioenergetics of hyperthermophile-mineral interactions is in its infancy and requires a better understanding of energy generation through mineral reduction and maintenance energy costs. This will require the input of microbiologists, geochemists, and bioenergetic modelers. My future research includes characterizing and modeling factors that influence growth, protein and gene expression analyses, and determining of the types of mineral transformations that take place using Mӧssbauer, FTIR, nano-XANES, XRD, and electron microprobe analyses. Another goal of our mineral transformation analyses is to establish sets of biosignatures that could be detected using in situ sensors.

Ver Eecke, H.C., D.S. Kelley, and J.F. Holden (2009) Appl. Environ. Microbiol. 73:242.