Magnetotactic bacteria discovered in deep ocean

Scientists have made an exciting discovery regarding magnetotactic bacteria, which possess the remarkable ability to align with Earth’s magnetic field. While these bacteria were previously observed in terrestrial and shallow water environments, recent analysis of a hydrothermal vent has demonstrated their survival in deep-sea conditions. This finding suggests that magnetotactic bacteria can thrive in environments that do not typically meet their preferred requirements. The research, published in Frontiers in Microbiology, sheds light on the bacteria’s ecological role on Earth and their potential significance in the search for extraterrestrial life.

Moreover, these bacteria leave behind evidence of their existence in rocks for billions of years and can provide valuable insights into the historical shifting of magnetic poles. This newfound discovery has raised hopes among researchers that magnetotactic bacteria may be found in unexpected locations, both on Earth and potentially on celestial bodies like Mars.

The bacteria’s unique ability to sense Earth’s magnetic field stems from the presence of magnetosomes—iron crystals enclosed within a membrane—which align themselves with the magnetic field and guide the bacteria’s movement like a compass. This alignment allows the bacteria to navigate along the Earth’s magnetic field lines, akin to trains on a magnetic track, heading either north or south. Furthermore, magnetotactic bacteria play a vital role in the biogeochemical cycling of crucial elements such as carbon, nitrogen, and phosphorus in nature. Although extensively studied on land and in shallow waters, their exploration in deep-sea environments has proven challenging due to the difficulties associated with collecting samples. In September 2012, a team of researchers, including scientists from the University of Tokyo, embarked on a scientific expedition to the southern Mariana Trough in the western Pacific Ocean.

Employing a remotely operated underwater vehicle called HYPER-DOLPHIN, they successfully retrieved a hydrothermal vent “chimney” from a depth of 2,787 meters (approximately 4.5 times the height of the Tokyo Skytree or over six times the height of the Empire State Building in New York). Hydrothermal vents form when seawater percolates into the ground, subsequently becoming superheated by magma to temperatures as high as 400° Celsius. The heated water then rises back up, carrying minerals and metals that accumulate to form chimneys. These structures create warm and nutrient-rich habitats, fostering a wide array of unique life forms.

Like a compass, the iron-containing magnetosomes in the bacteria align towards the Earth’s magnetic polls, compelling them to move in a north or south direction depending on which hemisphere they inhabit. Credit: 2017, Toshitsugu Yamazaki

Associate Professor Yohey Suzuki from the University of Tokyo’s Graduate School of Science expressed surprise at the discovery of magnetotactic bacteria living on the chimney of the hydrothermal vent. The researchers did not expect to find these bacteria in an environment lacking a clear, vertical chemical gradient, which is typically preferred by these organisms. The collected bacteria exhibited mainly bullet-shaped magnetosomes, suggesting a primitive form that has remained relatively unchanged for millennia. This finding indicates similarities between the current environment and the conditions on early Earth approximately 3.5 billion years ago when the ancestral magnetotactic bacteria likely emerged.

To collect the bacteria, a magnet was used to extract samples from the rim of the chimney. Genetic analysis revealed their relation to Nitrospinae bacteria, which are known for their role in carbon fixation in deep-sea environments but were not previously associated with magnetotactic behavior.

Deep-sea hydrothermal vents are not only intriguing due to the unique life they harbor but also because they provide a potential analog for habitats where extraterrestrial life may exist. The environment in which the bacteria were sampled resembles the conditions on Mars when flowing water was present on its surface around 3 billion years ago.

The fossilized remnants of magnetotactic bacteria’s magnetic particles, known as magnetofossils, can endure for billions of years within rocks. These magnetofossils offer valuable insights into ancient geomagnetic history and serve as promising candidates in the search for extraterrestrial life.

The Martian meteorite Allan Hills 84001, estimated to be around 3.6 billion years old, caused significant excitement in 1996 when it appeared to contain iron-crystal fossils resembling bacterial life. Although this claim has faced widespread controversy, Suzuki remains optimistic about future discoveries.

Magnetotactic bacteria provide clues about the early evolution of bacteria, and scientists hope to find evidence of their existence beyond Earth, potentially on celestial bodies such as Mars or icy moons. The ongoing exploration will continue to investigate various types and ages of rocks on Earth, previously not considered to be inhabited by these bacteria, in the quest for further evidence.

Source: University of Tokyo

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