Bacteria That Feeds on Metal Accidentally Discovered by Scientists

Researchers have discovered a new type of bacteria that eats metal, specifically, the element manganese.

The metal is one of the most abundant elements on Earth, with scientists predicting more than a century ago that microbes existed which feed on the substance as a source of fuel. Now researchers have finally found such a bacteria, according to a study published in the journal Nature.

"These are the first bacteria found to use manganese as their source of fuel," Jared Leadbetter, an author of the study from Caltech, 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."

The researchers say that the bacteria oxidizes the manganese, meaning it strips the metal of electrons, turning it black. This oxidization is harnessed to convert carbon dioxide into biomass, in a process known as chemosynthesis, enabling the bacteria to grow.

Scientists already knew about bacteria and fungi that oxidized manganese, however, until the latest study no one had demonstrated that it could fuel the growth of these kinds of organisms.

The discovery of the manganese-consuming bacteria was somewhat fortuitous. Leadbetter, a professor of environmental microbiology, had been conducting unrelated research using a chalk-like form of manganese.

Prior to leaving his Caltech office in Pasadena, California, a few months ago to work off campus, Leadbetter had left a glass jar covered in the chalk-like manganese in a sink to soak in tap water. Upon his return, he was surprised to discover that the jar was now blanketed in a black material.

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

Tests identified that the black substance was indeed oxidized manganese, which is commonly found in nature. The metal is never found as a free element in nature. Instead, it is usually combined with iron or found within minerals.

The researchers concluded that the manganese had been oxidized by a newly identified bacteria, dubbed Candidatus Manganitrophus noduliformans, which had most probably come from the tap water.

This is not surprising given that relatives of the new bacteria have been documented in underground water sources where some of Pasadena's drinking water comes from, according to Leadbetter.

bacteria, manganese oxide
An electron microscope image with false colorization showing tiny pieces of manganese oxide generated by the newly identified bacteria. Caltech/Hang Yu

The latest findings could help to explain why manganese oxides are sometimes found in water-distribution systems, which deliver drinking water to homes, businesses and other facilities.

"There is a whole set of environmental engineering literature on drinking-water-distribution systems getting clogged by manganese oxides," Leadbetter said.

"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."

Furthermore, the results could also shed light on the mysterious formation of strange, metallic balls of manganese—some as large as grapefruits—that have been documented on the seafloor across many parts of the world. The team speculate that microbes similar to the one they identified may play a part in the formation of the balls.

The manganese balls, or "nodules," are now being targeted by mining companies because many contain rare metals.

"This underscores the need to better understand marine manganese nodules before they are decimated by mining," Hang Yu, another author of the study from Caltech, said in the statement.