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Bioelectromagnetism

health efects of environmental MFs including extremely low-frequency (ELF)-MFs ranging from 1 to

300 Hz have been discussed on the basis of the “radical pair mechanism” (RPM; reviewed by Juutilainen

et al., 2018).

In this chapter, we review the current understanding of the efects of fuctuations and variations of

the GMF on living organisms. We discuss the further possibility that the efects of the GMF on living

organisms. We propose a hypothesis for explaining the link between the GMF reversals and the extinc­

tion and evolution of life on Earth and make proposals for future research.

6.2 Magnetic Sense

6.2.1 Primitive Magnetic Sense

Apart from gravity, the GMF is the only ubiquitous and relatively permanent element of the environ­

ment, thus being a great source of information for organisms (Erdmann et al., 2021). For certain kinds of

bacteria, the only way to survive is to sense the GMF and move to a place suitable for survival. Te mag­

netosensitivity of aquatic bacteria have been found in 1958 by an Italian medical doctor, Salvatore Bellini

who was working in the Institute of Microbiology at the University of Pavia, Italy (Bellini, 1963a,b). He

serendipitously discovered magnetosensitive bacteria at that time while examining water samples from

sources around Pavia for pathogens (Frankel, 2009). Whereas Bellini was the frst discoverer of mag­

netosensitive bacteria, his discovery was lost until an American scientist, Blakemore rediscovered the

phenomenon in 1975 (Blakemore, 1975). Tese bacteria can sense the GMF and swim north or south.

Due to their characteristics, these bacteria are called “magnetotactic bacteria.” Magnetosensitivity and

magnetotaxis of bacteria are the same behavior (Frankel, 2009). Blakemore (1982) had the advantage

of electron microscopy by which he discovered the “magnetosomes.” Tis instrument was apparently

unavailable to Bellini at that time (Frankel, 2009). Nevertheless, it is clear that Bellini’s manuscripts

document a valid scientifc discovery, and support his claim to the discovery of magnetosensitive/mag­

netotactic bacteria (Frankel, 2009).

Subsequent research by Frankel et al. (1979) shows that magnetotactic bacteria contain 10–20 micro­

scopic ferromagnetic substances in their bodies called “magnetite” (~50 nm) and they are thus aligned

passively with the GMF lines. Endogenous magnetite has a structure in which fatty acid covers mag­

netite (Fe3O4) or iron sulfde (Fe3S4), and each is covered with an organic thin flm, forming a long

chain-shaped or beaded structure of a single magnetic domain (~0.05–1.2 μm) called “magnetosomes”

as a whole (Schüler, 2002). It is the “magnetic compass needle” that exists inside the body just like nano

biomagnets (Uebe and Schüler, 2016). Magnetosomes detect the deviation from the direction of the

MF as torque. Torque is the rotational force, which is the minimum energy when bacteria swim in the

direction of the MF lines. Terefore, an external MF acting on magnetic moments can arrange and

rotate these small bacteria according to the MF lines. Tis happens in both horizontal and vertical MFs

(Kalmijn and Blakemore, 1978). Te general properties of magnetite depend on the size and shape of the

particles (frst described by Kirschvink and Gould, 1981). Spin interactions cause the spins of adjacent

atoms to align, thus forming domains with all spins parallel. Even smaller particles are superparamag­

netic: at room temperature, their magnetic moment fuctuates as a result of thermal agitation, but it can

easily be aligned by an external MF (Kirschvink and Walker, 1985).

Key functions of magnetosome biogenesis are encoded by about 30 genes that are clustered in a

genomic “magnetosome island,” although additional auxiliary functions are contributed by general

cellular metabolic and regulatory pathways, including aerobic and anaerobic respiration (Uebe and

Schüler, 2016). Surprisingly, a non-magnetotactic bacterium has recently been “magnetized” through

the heterologous expression of genes that encode the magnetosome biogenesis pathway, which is a

proof-of-principle demonstration that non-magnetotactic bacteria that are more facile for laboratory

investigation could be “magnetized” to provide new models for genetic dissection and synthetic biology

(Uebe and Schüler, 2016).