CAREER: Microbial Mineral Oxidation in a Temperate Marine Sediment: Quantifying the importance of extracellular electron transfer to sediment sulfur biogeochemistry

About This Grant

Many marine sediment microbes are known to recycle fixed carbon substrates, producing CO2. However, there is building evidence that many marine sediments can also serve as a sink for CO2. The microbial processes that fuel this “dark” carbon fixation are poorly understood. Mineral oxidation, such as iron or sulfur oxidation, are thought to be important drivers of dark carbon fixation, but poor characterization of these metabolisms means we lack the tools necessary to identify and quantify these physiologies in the field. This is especially true for detection with commonly used sequencing-based approaches, which depend on having marker genes or proteins that inform the metabolic potential for a process. This work is investigating biomarkers for mineral oxidation in distinct microbial lineages, thus expanding our current understanding of the breadth and diversity of mineral oxidation mechanisms, and the role they play in carbon cycling and sequestration in marine sediments. In addition to the environmental relevance of these organisms and processes, the ability to oxidize solid phase minerals, often lends itself to interaction with redox active surfaces such as poised potential electrodes. As such, understanding these mechanisms also provides insight into the potential for microbe electrode technologies. This grant is investigating the genes and pathways used by several marine sediments microbes for oxidative extracellular electron transfer (EET) for mineral oxidation. The subject microorganisms were previously isolated from Catalina Harbor and are known to have unique electrochemical properties. Genomically, they lack homology to known EET pathways. Application of either high throughput genetic techniques (Tn-Seq), or gene expression studies (RNA-seq), depending on the specific strain studied is being used for gene identification. Putative biomarkers identified in this work are being confirmed genetically. The education component of this grant uses one of these strains in a course based undergraduate research experience for a second semester Intro-biology lab. The physiologic and genomic work performed thus far point to a potential role for EET in various sulfur-oxidizing metabolisms. Investigating the role of sulfur minerals in supporting microbial metabolism, is occurring using microbial anabolism with bio-orthogonal non-canonical amino acid tagging (BONCAT) in parallel with either spectroscopic techniques (Raman, XRD, etc.) or fluorescent activated cell sorting coupled to metagenomic sequencing in Catalina harbor sediments. As many of the microbes isolated from this sediment are capable of lithotrophic interaction with sulfur, it is hypothesized that sulfur species are playing an important role in supporting microbial metabolism, and dark carbon fixation in this system—likely using EET to use or storing solid phase sulfur minerals, and/or developing a conductive network to bridge spatial gaps between the oxidants and reductants. This project is cofunded by the Biological Oceanography and Geobiology and Low-temperature Geochemistry Programs. 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.