Previous investigations have explored the effects of hypermagnetic fields, that is, fields in excess of the Earth’s background geomagnetic field strength of approximately 50 µT, on Escherichia coli (E. coli). Conversely, this study investigates the effects of hypomagnetic field conditions, that is, fields below the geomagnetic background intensity, on the growth of E. coli K12 by using a hypomagnetic chamber to shield cultures, with a measured residual magnetic field inside the chamber of 19 nT. When grown in rich media from a semi-anaerobic, stationar y-phase starting culture under geomagnetic and hypomagnetic conditions, the lag phases of E. coli were approximately 86 minutes and 132 minutes, respectively. Despite this increase in lag phase, exceeding two E. coli doubling times, the log-phase growth rate of E. coli was identical under both geomagnetic and hypomagnetic conditions. In addition to demonstrating a biologically relevant sensitivity to magnetic field parameters in the hypomagnetic direction, this represents a much greater absolute magnetosensitivity, with a deviation of only 50 µT between the hypomagnetic and geomagnetic conditions, than has previously been demonstrated for E. coli.

Electron spin-dependent chemical reactions in proteins, often discussed under the ‘radical-pair mechanism’, have been studied for decades and remain the leading microscopic proposal for magnetic field sensing in biology. Yet the essential physics is often obscured by the complexity of realistic models. In this work, we present a physicist-friendly primer on the simplest radical-pair Hamiltonian that already captures many of the mechanism’s best-known qualitative features. The contribution of this work is fourfold. First, we place on record a complete analytical solution of this toy model, which has previously been studied extensively, mostly through numerical and partial analytical approaches. Working in the experimentally relevant singlet–triplet basis, we derive closed-form expressions for the instantaneous singlet population and for two related time-averaged singlet yields. Second, we introduce a new interpretation of these results that makes several familiar features of radical-pair physics transparent. In particular, we show that the dynamics admit a bright–dark decomposition (in the sense of spin mixing), similar to structures widely studied in atomic and optical physics, for example in electromagnetically-induced transparency. Third, through this bright–dark perspective, we clarify experimentally relevant features of the toy model. In particular, we show that the so-called ‘low-field effect’ arises from a coherence term between bright and dark sectors, and that the special role of zero field is best understood as a phase-locking phenomenon rather than merely as enhanced mixing. The same framework also makes it possible to explicitly identify the ‘pathway that opens’, as per the chemists’ language, once a nonzero field is applied. Fourth, we import methods from quantum magnetometr y, developed in the context of technological quantum sensing, to obtain further insight into the model. This allows us to clarify the role of initial state preparation and the trade-off between coherent phase accumulation and time-averaging penalties. The resulting toy model serves both as an analytically tractable benchmark and as a conceptual starting point for future work incorporating a true open quantum system treatment, unequal singlet and triplet decay rates, and fully directional magnetic field control.

QBI's response to the NSF Tech Labs Request for Information

In this study, the fluorescent protein MagLOV2 was characterized for how its brightness changes depending on the strength of an applied external magnetic field in living bacterial cells. At very low magnetic field strengths, fluorescence increases as the field becomes stronger. However, at moderately higher field strengths, the trend reverses, and the fluorescence decreases with further increases in the magnetic field before eventually leveling off. This complex response is consistent with established models of a process known as the “radical pair mechanism”, which is a leading hypothesis for how biological molecules can be affected by weak magnetic fields. The results suggest that the sensitivity of MagLOV2 to magnetic fields is consistent with an underlying quantum mechanism that operates in the complex environment of a living cell.

Despite decades of reports of weak magnetic field effects in biology across the tree of life and on a broad range of cell types, the evidence to date remains met with skepticism. To remedy this, we present open-data, large-scale, and varied morphological evidence that Xenopus laevis embryo development is accelerated in a well-engineered, environmentally-calibrated hypomagnetic field of less than 1 nT. These data imply that basal tadpole physiology can sense and react to the absence of Earth’s minute magnetic field of approximately 50 μT. The effect is significant, as demonstrated by a variety of statistical measures. As no definitive biophysical mechanism has been identified to account for its occurrence, this study raises the question of which mechanism provides the most plausible explanation. How that question is answered may have implications in a variety of fields, including human health, behavioral ecology, and space exploration.