Bacteria That Feeds on Metal Discovered by Accident

​​A team of microbiologists has found a bacteria that feeds on manganese and uses the metal as its source of calories. This type of microbes was first believed to exist more than a hundred years ago, but none have been discovered so far.

“These are the first bacteria found to use manganese as their source of fuel,” says Jared Leadbetter, professor of environmental microbiology at Caltech who collaborated with postdoctoral scholar Hang Yu in the new study. “A wonderful aspect of microbes in nature is that they can metabolize seemingly unlikely materials, like metals, yielding energy useful to the cell.”

The research also unveils the bacteria can use manganese to transform carbon dioxide into biomass, a process known as chemosynthesis. Earlier on, scientists knew of bacteria and fungi that had the ability to oxidize manganese or strip it of electrons, but they had only predicted that the microbes might be capable of harnessing the process to fuel growth.

And This is How New Bacteria Was Found

Leadbetter discovered that the bacteria by accident after carrying out unrelated experiments using a light, chalk-like form of manganese. He had left a glass jar stained with the substance to soak in tap water for a few months, and when he returned to the lab, the jar was coated with a dark material.

“I thought, ‘What is that?'” he explains. “I started to wonder if long-sought-after microbes might be responsible, so we systematically performed tests to figure that out.”

The black material was actually oxidized manganese triggered by newfound bacteria that had probably come from the tap water.

“There is evidence that relatives of these creatures reside in groundwater, and a portion of Pasadena’s drinking water is pumped from local aquifers,” Leadbetter says.

Manganese is one of the most-found elements on Earth. Its oxides take the form of a dark, clumpy substance and are rather common, being found in subsurface deposits and in water-distribution systems.

Manganese oxide nodules produced by the bacteria discovered by the Caltech team. [Image: Hang Yu/Caltech]
“There is a whole set of environmental engineering literature on drinking-water-distribution systems getting clogged by manganese oxides,” Leadbetter explained. “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.”

Manganese Oxide – Figuring What Makes it

The discovery helps scientists better understand the geochemistry of groundwater. It is already known that bacteria are able to degrade pollutants in groundwater, a process known as bioremediation. When doing this, a few key organisms would reduce manganese oxide. Researchers have tried to find out where the manganese oxide comes from in the first place.

“The bacteria we have discovered can produce it; thus they enjoy a lifestyle that also serves to supply the other microbes with what they need to perform reactions that we consider to be beneficial and desirable,” says Leadbetter.

The research discoveries also have possible significance to understand manganese nodules that cover the seafloor. Lately, mining companies have been creating plans to harvest and exploit these nodules, because rare metals are usually found concentrated within them.

However, there’s not much information regarding the way the nodules form. Yu and Leadbetter wondered whether similar microbes found in freshwater might also play a role in such a process.

“This discovery from Jared and Hang fills a major intellectual gap in our understanding of Earth’s elemental cycles, and adds to the diverse ways in which manganese, an abstruse but common transition metal, has shaped the evolution of life on our planet,” says Woodward Fischer, professor of geobiology at Caltech, who was not involved with the study.

​The study has been published in the journal Nature, titled ‘Bacterial chemolithoautotrophy via manganese oxidation,’ and authored by Hang Yu and Jared R. Leadbetter.

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