Seminars Archive

A possible magnetotactic organ in the arm of octopus: Synchrotron radiation informs biology

Andrea Degl'Innocenti
Istituto Vinciano per le Scienze, Viale Palmiro Togliatti 49, 50059 Sovigliana-Spicchio, Vinci (FI), Italy

Abstract
Magnetoception is the ability to detect magnetic fields, a rare sense in the animal kingdom. Organisms that sense magnetic fields use either special proteins or magnetic minerals, often housed in magnetotactic bacteria (MTB) that live in symbiosis with their hosts. Some mollusks, including octopuses, are suspected of being able to discern magnetic gradients - yet the molecular underpinnings of such capabilities remain elusive. We identified a putatively magnetoceptive structure in an octopus arm. Upon dissection of fresh tissue, the area (or immediately nearby ones) will follow a magnet, even in absence of physical contact. From there, we isolated RNA for putatively magnetoceptive proteins, as well as for microbes compatible with MTB. Histological preparations detected bacterium-like particles in smears of the structure, and spots in iron-specific staining were identified at expected locations after sectioning. The same preparations, observed in high-resolution brightfield microscopy, show stereotypically arranged ensembles of yellowish particles reminiscent of bacteria. Strikingly, at Elettra's TwinMic beamline, we observed micrometer-scale specks of ferrimagnetic material via X-ray fluorescence (XRF) mapping, matching in position and shape with putative bacteria. While these features are consistent with MTB, alternative explanations remain possible, such as iron/nickel-rich sand particles that could have been ingested or introduced as contamination. Upcoming beamtime at the NanoMAX (MAX IV) facility will extend our XRF analyses, providing higher-resolution data on crystal structure and the oxidation state of iron/nickel, aiming to definitively identify the nature of the magnetic deposits. The possibility of employing other synchrotron techniques to further elucidate the case for magnetoception in octopus will be discussed during the seminar.