The identity of a magnetic sensor in animals remains enigmatic. Although the use of the geomagnetic field for orientation and navigation in animals across a broad taxonomic range has been well established over the past five decades, the identity of the magnetic-sensing organ and its structure and/or apparatus within such animals remains elusive—‘a sense without a receptor’. Recently, Vortman and colleagues proposed that symbiotic magnetotactic bacteria (MTB) may serve as the underlying mechanism behind a magnetic sense in animals—‘the symbiotic magnetic-sensing hypothesis’.
Magnetotactic bacteria are a special type of bacteria whose movement is influenced by magnetic fields, including the Earth’s.
Animals that sense Earth’s magnetic field include sea turtles, birds, fish and lobsters. Sea turtles, for example, can use the ability for navigation to return to the beach where they were born.
Learning how organisms interact with magnetic fields can improve humans’ understanding of how to use Earth’s magnetic fields for their own navigation purposes. It can also inform ecological research into the effects of human modifications of the magnetic environment, such as constructing power lines, on biodiversity. Research into the interaction of animals with magnetic fields can also aid the development of therapies that use magnetism for drug delivery.
In the article, the researchers review the arguments for and against the hypothesis, present evidence published in support that has arisen in the past few years, as well as offer new supportive evidence of their own.
Their new evidence comes from Fitak, who mined one of the largest genetic databases of microbes, known as the Metagenomic Rapid Annotations using Subsystems Technology database, for the presence of magnetotactic bacteria that had been found in animal samples.
Previous microbial diversity studies have often focused on large patterns of the presence or absence of bacteria phyla in animals rather than specific species.
Fitak found, for the first time, that magnetotactic bacteria are associated with many animals, including a penguin species, loggerhead sea turtles, bats and Atlantic right whales.
For instance, Candidatus Magnetobacterium bavaricum regularly occurred in penguins and loggerhead sea turtles, while Magnetospirillum and Magnetococcus regularly occurred in the mammal species brown bats and Atlantic right whales.
According to Fitak, researchers still don’t know where in the animal that the magnetotactic bacteria would live, but it could be that they would be associated with nervous tissue, like the eye or brain.
Before joining UCF in 2019, Fitak worked for more than four years as a postdoctoral researcher at Duke University performing experiments to identify genes related to a magnetic sense in fish and lobsters using modern genomic techniques.
The hypothesis that animals use magnetic bacteria in a symbiotic way to gain a magnetic sense warrants further exploration but still needs more evidence before anything conclusive can be stated.
References: Eviatar Natan et al, Symbiotic magnetic sensing: raising evidence and beyond, Philosophical Transactions of the Royal Society B: Biological Sciences (2020). DOI: 10.1098/rstb.2019.0595 link: https://royalsocietypublishing.org/doi/10.1098/rstb.2019.0595