Metabolic-State-Dependent Magnetic Field Effects on Endogenous Flavin Autofluorescence in Escherichia coli

We demonstrate that endogenous autofluorescent molecules in Escherichia coli exhibit fluorescence changes exceeding 10% in response to a 25 mT magnetic field under specific physiological and excitation conditions. Fluorescence spectral analysis strongly supports a flavin origin of the magnetically sensitive signal, with a slight blue shift relative to free flavin suggesting a protein-associated population. The analysis further suggests that this magnetic response originates from a flavin-related component contributing only part of the total cellular autofluorescence. This implies that the magnetic field effect exceeding 10% observed in total cellular autofluorescence represents an ensemble-averaged response, and that the intrinsic magnetic field effect within the magnetically sensitive flavin population may be substantially larger. Notably, the magnetic field effect is strongly suppressed by carbon-source supplementation. These findings indicate that the manifestation of the magnetic field effect is associated with the cellular physiological or metabolic state. The field-induced negative fluorescence response and the saturation of the magnetic-field dependence support the radical-pair mechanism and are consistent with a triplet-born radical-pair reaction. This work provides a framework for identifying endogenous biomolecular candidates exhibiting large intracellular magnetic field effects and suggests a new route toward label-free readout of cellular metabolic states based on flavin magnetosensitivity.