Initial Engineering Model Development for Sulfate Reducing Bacteria Colonization Potential Related to Forward Contamination and Ecosynthesis 2008-01-1981

This research is intended to provide contamination and ecosynthesis researchers with an engineering development tool for understanding the productivity of metabolically active low temperature brine habitats as potential sites for bacterial colonization by forward contaminating Earth organisms. The specific extremophile microbial culturing conditions targeted were psychrophilic (low temperature), halophilic (high salt), high ambient sulfur, and anaerobic. These low temperature or freezing point suppressed brine habitats with high ambient sulfur concentrations have been suggested as potential subsurface water resources on both Mars and Europa, and may be common among potentially viable extant water environments in the outer solar system. This initial proof of concept study provides a high sulfate brine matrix habitat (media) and uses aqueous phase tracking of sulfate (SO₄^2-) and acetate (CH₃COO^-) consumption as the primary measure of the activity of Sulfate Reducing Bacteria (SRB) in digesters and thus metabolic viability. The digesters are intended to be a physical modeling tool to assist researchers in developing a better understanding of the limits to viability and potential productivity of these brine habitats as they relate to forward contamination and colonization potential when exposed to microbial inoculation associated with human waste exposure.

Prior to this study, equipment and techniques for large scale production of SRB biomass at or below 4°C in marine brine were not well documented, particularly from a practical habitat engineering sense. One of the primary contributions of this study is to provide a documented and practical case study for culturing equipment and technique development, as well as developing a reasonable baseline expectation for substrate utilization performance of SRB cultures under these and/or similar conditions. Specifically, proof of concept testing was conducted at a temperature of 4°C ± 0.15°C, a salt concentration 2.5% as NaCl (simulated marine salt water), a pH range of 7.8 to 8.5, and an oxidation-reduction potential (ORP) of approximately −480mV using a Pt electrode (equivalent to −280mV using a standard H⁺electrode). Subsequent, studies have extended the range of active digester culturing of SRB to below 0°C, and some results for performance in this temperature range are also included.