Are bacteria responsible for the magnetic ‘sixth sense’ of marine animals?

A new paper has suggested that a symbiotic relationship with magnetotactic bacteria, capable of sensing the Earth’s magnetic field, may be behind the incredible navigational skills of marine animals including penguins, turtles and whales. So is this what is going on? Or is it too soon to tell?

An example of a magnetotactic bacteria, which is now believed to be responsible for magnetic sensing in marine animals

Since the invention and advancement of satellite tagging marine animals, one of the most surprising discoveries is that many ocean inhabitants have a remarkable sense of navigation. This includes whales, seabirds, fish and sea turtles, who have all been shown to make consistent long-range migrations across entire ocean basins, often with astonishing accuracy. Some, including seabirds and turtles, are even capable of returning to the nesting site or beach where they were born to have their own offspring decades later. The only real explanation for how marine creatures are able to do this is via geomagnetic navigation, where they are able to sense the Earth’s magnetic field to orient themselves. How exactly they are able to do this has remained a mystery for almost 50 years, but a newly published paper has suggested that the secret behind this skill may be a symbiotic relationship with geomagnetic bacteria.

An intriguing hypothesis

This new hypothesis, into how marine animals are able to sense the Earth’s magnetic field, comes from an international group of researchers from the UK, USA and Israel. In their recently published paper, they suggest that magnetoreception in animals is only possible via a symbiotic relationship with special bacteria, known as magnetotactic bacteria, who are capable of orienting themselves using the Earth’s magnetic field. They are able to do so via specialised organelles called magnetosomes, which form chains across the cell and act as magnets which are attracted the Earth’s magnetic field lines. They believe that by having these bacteria within their bodies animals would therefore be able to sense the Earth’s magnetic field through these bacteria. However at this stage it is important to note this is just a theory and is yet to be fully supported by the scientific community.

An example of a chain of magnetosomes running through the cell of a magnetotactic bacteria

Supporting evidence

The main evidence in support of the researchers hypothesis comes from specialised genetic work carried out by Dr Robert Fitak at the University of Central Florida in America. Using one of the world’s largest genetic databases of microbes found in animals, known as the Metagenomic Rapid Annotations using Subsystems Technology database, he searched for magnetotactic bacteria that had been found within certain magnetoreceptive animals including whales, sea turtles and penguins.  “The presence of these magnetotactic bacteria had been largely overlooked, or ‘lost in the mud’ amongst the massive scale of these datasets” he explained in a recent press release. Therefore by searching hard for specific species of bacteria he was able to identify multiple species in different animals. Dr Fitak now wants to develop a new genetic test to be able to identify magentotactic bacteria in more animals so the team can keep gathering more evidence to support their theory.

Counter arguments

The main argument against a symbiotic relationship between animals and magnetotactic bacteria is that there is currently no clear mechanism by which animals obtain or store the bacteria within their bodies, let alone how they are able to interact with and utilize them. It is also important to note that although they are found in some animals, doesn’t mean they are used by them, because all animals carry millions of microscopic organism on or within them and many are just passive passengers.

Loggerhead sea turtles are one species who have been shown to have magnetotactic bacteria, but that doesn’t necessarily mean they use them for navigation

Others argue that defining it as a symbiotic relationship is misleading because there is no clear way the bacteria benefit from the relationship and because magnetosomes do not require the bacteria to be alive in order to properly orientate, the bacteria may actually die off and the animals could just be incorporating magnetosomes into their own bodies instead. So whilst this new theory is a good start to finding out how magnetoreception in animals work, there is still lots of research that needs to be done to prove it.

Potential implications

If magnetotactic bacteria are eventually proved to be the underlying cause of magnetoreception in animals it could have some big implications, especially in the marine environment. For years, very little consideration has been given to laying powerlines below or on the seafloor. It is a growing industry and is necessary for things like long-range telecommunications and transporting energy from offshore renewable energy sites to land. However because of how little we know about magnetoreception in marine animals like turtles, whales and seabirds we don’t know what negative effects this could be having on the local marine environment. Therefore better understanding how it works is crucial in mitigating any potential long term impacts. There is also a chance that magnetotactic bacteria could play a role in medical therapies for humans in the future as well.

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