A Two-Protein Chemoreceptor Complex Regulates Oxygen Thresholds in Bacterial Magneto-Aerotaxis

Bacteria in changing environments rely on motility and sensory mechanisms to locate optimal conditions. This process depends on specialized chemoreceptors to sense environmental stimuli. Exceptionally high numbers of chemoreceptor genes are present in magnetotactic bacteria (MTB), which combine magnetic alignment via intracellular magnetic nanoparticles (magnetosomes) and oxygen sensing for a unique navigation strategy toward low-oxygen zones, called magneto-aerotaxis. However, chemoreceptors for aerotaxis in MTB have not been experimentally identified. This study examines chemoreceptors in the model MTB Magnetospirillum gryphiswaldense. Gene deletion analysis shows that M. gryphiswaldense relies on a complex and partly redundant set of chemoreceptors to sense oxygen. Within this diverse repertoire of chemoreceptors, a receptor formed by two interacting proteins is identified that plays a key role in aerotaxis. Interaction assays and microscopy confirm that both proteins interact within polar-lateral regions in the cell. Moreover, genetic, biochemical, and motility experiments demonstrate that the chemoreceptor complex promotes a cellular response away from oxygen via the redox cofactor flavin adenine dinucleotide (FAD), independent of magnetic fields. These findings provide first insights into how MTB control oxygen sensing at the molecular level, shedding light on the mechanisms underlying bacterial navigation and highly complex chemosensory systems.