Metal-Eating Bacteria Discovered By Accident Over A Century After First Predicted
CHIPS OF MANGANESE. KIM CHRISTENSEN

By Jack Dunhill 16 JUL 2020


Bacteria tend to have some pretty unusual tastes in their chosen food. From chowing down on leftover takeaway to sitting on the side of deep oceanic thermal vents, we’re constantly discovering different ways they choose to get their energy.

In a new paper published in Nature, researchers from Caltech have discovered bacteria that can metabolize manganese – one of the most abundant elements on the Earth’s surface – as their main source of energy. Made up of two species, the bacteria could use the metal and produce energy to sustain and grow in the most minimal of environments. Despite scientists predicting it for over a century, this is the first bacteria shown to use manganese in chemosynthesis.

Impressively, Professor Jared Leadbetter, professor of environmental microbiology at the California Insitute for Technology (Caltech), said he made this discovery by accident. After being out-of-office for several months and leaving a jar filled with manganese and tap water from a previous experiment, the professor returned to find the jar coated with a black substance. He believed it could be the result of the fabled bacteria that could metabolize manganese, and his team immediately began testing the contents of the jar.

They discovered two new bacterial species living in the tap water were using the left-over manganese as food, creating a black byproduct later identified as manganese oxide.

Some bacteria are known to oxidize manganese, producing manganese oxide, which is found all along the Earth’s subsurface, but they have never shown to use it in metabolism. Metabolism is essential for growth, and discovering that some species can use metals as food for growth is a long-awaited breakthrough.

"These are the first bacteria found to use manganese as their source of fuel," Professor Leadbetter said in a statement. "A wonderful aspect of microbes in nature is that they can metabolize seemingly unlikely materials, like metals, yielding energy useful to the cell."

Manganese oxide is a problem for water distribution systems, as it accumulates and blocks waterways. Understanding how the oxide deposits build up would help in preventing it, but their origins have eluded scientists until now.

Black residue manganese oxide can clog water systems. 

Ihor Matsiievskyi on Shutterstock

"There is a whole set of environmental engineering literature on drinking-water-distribution systems getting clogged by manganese oxides," said Leadbetter. "But how and for what reason such material is generated there has remained an enigma. Clearly, many scientists have considered that bacteria using manganese for energy might be responsible, but evidence supporting this idea was not available until now."

Despite its pipe-clogging drawbacks, researchers have found manganese oxide to play an important role in reducing pollutants in groundwater. Key bacterial species use it in a process called bioremediation to degrade and remove pollutants, and so the availability of the oxide might have direct links to how successful bioremediation is in water supplies.

Alongside understanding the ecosystem of subsurface water systems, this discovery might go much deeper. For centuries, large metallic nodules have been found along the seabed and have puzzled scientists. Mainly consisting of manganese but also containing concentrated rare metals, these balls have been of interest to biologists and mining companies alike. Through the discovery of manganese-metabolizing bacteria, it’s possible bacteria similar to those isolated in Leadbetter’s lab are responsible. If researchers can understand the nodules' origins, they may be able to help protect the local ecosystems from excessive mining. Postdoctoral scholar Hang Yu, who collaborated with Leadbetter on the study, said: "This underscores the need to better understand marine manganese nodules before they are decimated by mining."