Elucidating Mechanisms of Metal Sulfide-Enabled Growth of Anoxygenic Photosynthetic Bacteria Using Transcriptomic, Aqueous/Surface Chemical, and Electron Microscopic Tools

Purple bacteria convert light energy into chemical energy through anoxygenic photosynthesis. Purple sulfur bacteria (PSB) are a sub-group of purple bacteria, coupling the oxidation of reduced sulfur species to phototrophic growth. While PSB are recognized as key drivers of the sulfur cycle in various ecosystems (e.g., meromictic lakes, inland seas, and marine basins), their metabolic capability and flexibility are not fully understood. The research team's recent work demonstrated robust autotrophic growth of PSB strains using solid-phase transition metal sulfide (TMS) as sulfur and electron donors. Significantly, this finding reveals PSB’s remarkable potential in scavenging electrons directly from solid-phase substrate and close ties with TMS, which naturally occur in their niches, meriting further investigations. As such, the team will examine the PSB-TMS interactions and relevant mechanisms systematically. This work may have key implications for geochemistry and bioelectrochemistry, through providing new constraints for ancient and modern metal-sulfur biogeochemical cycles, establishing new models for bacterial extracellular electron transfer research, and demonstrating the potential synergy between nanoparticle photochemistry and microbial energy demand. The main research questions to be addressed in this study are: (i) if all TMS phases may enable the autotrophic growth of PSB as sole sulfur and electron donors; and (ii) what molecular mechanisms are involved in the PSB-TMS interactions. The research team will use a combination of transcriptomic sequencing, transmission electron microscopy coupled with advanced spectroscopy and cryo-techniques, and various aqueous/surface chemical analytical tools to resolve these questions. To maximize the impact of their work on society, they will incorporate synergistic outreach and mentoring activities. For example, they will create a series of short animation videos (to be hosted on YouTube) to disseminate the main results of this work. They will also develop an open-access Environmental Nanoscience tutorial. The long-term goal for these outreach activities is to create a robust pipeline for cross-disciplinary STEM research and to train a diverse group of students into a competent STEM workforce. 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.