(CNN)Scientists have discovered a type of bacteria that eats and gets its calories from metal, after suspecting they exist for more than a hundred years but never proving it.
Now microbiologists from the California Institute of Technology (or Caltech) accidentally discovered the bacteria after performing unrelated experiments using a chalk-like type of manganese, a commonly found chemical element.
Dr. Jared Leadbetter, professor of environmental microbiology at Caltech in Pasadena, left a glass jar covered with the substance to soak in tap water in his office sink, and left the vessel for several months when he went to work off campus. When he returned, Leadbetter found the jar coated with a dark material.
"I thought, 'What is that?' " Leadbetter explained in a press release. "I started to wonder if long-sought-after microbes might be responsible, so we systematically performed tests to figure that out."
Researchers discovered that the black coating found on the jar was oxidized manganese which had been generated by newly discovered bacteria most likely found in 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," he said.
In new research published in Nature journal on Tuesday, scientists note that these are the first bacteria to use manganese as an energy source.
"These are the first bacteria found to use manganese as their source of fuel," Leadbetter said. "A wonderful aspect of microbes in nature is that they can metabolize seemingly unlikely materials, like metals, yielding energy useful to the cell."
The new research also reveals that the bacteria can use manganese for a process called chemosynthesis, which converts carbon dioxide into biomass.
Researchers had speculated that unidentified microbes could harness the process to spur growth, but only knew of bacteria and fungi that could do so.
Scientists believe the findings will help them better understand groundwater, and water systems which can become clogged by manganese oxides.
"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."
Researchers also believe that the discovery could help us to understand manganese nodules -- large metallic balls which can reach the size of a grapefruit and are often found on the sea floor. The balls, which often contain rare metals, are sometimes harvested from the ocean floor, but little is understood about them.
"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," said Woodward Fischer, a professor of geobiology at Caltech, in a statement. Fischer was not involved with the study.