EAGER: The Bacterial Magnetosome may be a Potential Energy-Harvesting Pseudo-organelle for Magnetotrophy

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Magnetotactic bacteria (MTB) have evolved a unique suite of genetically-encoded proteins that are used to synthesize magnetic crystals within an intracellular compartment called the magnetosome. The conventional wisdom is that the magnetosome functions as a sort of internal compass enabling these cells to navigate to their ideal niche using the Earth's magnetic field as MTB swim through bodies of water. While this is an elegant explanation for magnetotaxis, the disparity between the high cost of synthesizing the magnetosome and infrequent alignment of MTB in nature suggests another function. This proposal will investigate the potentially transformative hypothesis that the magnetosome is not used for navigation/orientation but rather it is part of a previously unknown form of metabolism. If this hypothesis is validated then this would add a radically different form of metabolism (magneto-trophy) to established pathways to generate energy like autotrophy and heterotrophy. This new form of metabolism would actually be widespread because MTB are found in just about any environment with liquid water and these bacteria evolved billions of years ago. Knowledge gained from this research will be of great interest to educators across broad disciplinary bounds and promote the progress of science by helping to address fundamental questions integral to the connection between life science and physical science. These research activities will promote STEM training for underrepresented minority students as well as high school teachers embedded in the investigators' labs. Experiments will be performed to test whether the magnetosome plays a role in generating metabolic energy for MTB. Custom-made growth chambers will be used to culture MTB under a range of external magnetic-field strengths. Bacteria specimens will include wild-type strains of MTB and mutants that lack the genetic repertoire to synthesize their internal magnets. Magnetic measurements will be used to determine the presence (or absence) of the magnetosome and characterize the field-strength of internal magnetite in wild-type cells. Bacteria growth and activity will be monitored through absorbance measurements, cell counts, swimming speed, and assays for energy-carrying molecules. Omics and incorporation of isotopically-labeled compounds for wild-type versus mutant strains will permit identification of gene networks and products (proteins and metabolites) impacted by magnetic fields. Integration of data from these distinct yet complementary experiments will allow to carefully test the novel hypothesis that the magnetosome evolved to maximize energy uptake and/or endure in organic-carbon depleted environments that MTB often occupy in nature.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.