RII Track-4: Physiology of Sulfate-Reducing Bacteria under Energy-Limiting conditions

Bacteria have the ability to survive long periods of time under energy-limiting conditions, common in natural environments. To understand the fundamental aspects of energy limitation, bacteria can be studied in cultures for months to years without re-supplying the medium with energy sources. This project aims to study long-term cultures of sulfate-reducing bacteria (SRB), which drive the sulfur and carbon biogeochemical cycles in anoxic environments.

The proposed research will investigate the integrity of the cell and outer membranes of SRB and quantify metabolic processes to gain physiological insights into the long-term survival of SRB. This project will advance fundamental knowledge about long-term survival of microorganisms in anoxic environments. The project is also of importance for the economically vital processes that are influenced by SRB, such as the corrosion of iron infrastructure, wastewater treatment, and bioremediation of metal contaminated environments.

This fellowship will improve 1) STEM education through the delivery of lectures on high-resolution imaging to graduate courses, 2) the research capacity of the PI, and 3) the research infrastructure at the University of Nevada, Las Vegas.

The goals of this project are to characterize the extended life cycle of sulfate-reducing bacteria and to decipher the role of sulfide mineral crusts in preserving the viability of SRB in their extended life cycle. Our preliminary experiments have indicated that mineral-encrusted bacteria can be preserved alive for several years and regrow in fresh medium when non-encrusted cells of similar age do not regrow.

The proposed research will characterize the metabolic and physiological changes in mineral-free and encrusted sulfate-reducing bacteria in the long-term stationary phase. It will also identify the early steps of mineral crust formation at the surface of cells and the steps of mineral crust removal when cells regrow in fresh medium. Transmission electron microscopy (TEM) will be used to image the integrity of the cells and their membranes and cell wall at high resolution, while electron diffraction will be used to gain information about the mineral phases forming around cells.

Super resolution fluorescence microscopy (iPALM) will be used to localize and quantify metabolic processes such as new protein synthesis, proton gradient formation and adenosine triphosphate synthesis during the extended life cycle of mineral-free and encrusted SRB. This project will lead to a better understanding of long-term survival of sulfate-reducing bacteria and of the role of sulfide minerals in preserving long-term viability of SRB, which contribute to the formation of those minerals.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.