Caltech microbiologists have observed bacteria that feed on manganese and use the metal as their source of calories. Such microbes were expected to exist over a century ago, but none had been found or explained about it so far.
“These are the first bacteria discovered to use manganese as their source of fuel,” says Jared Leadbetter, professor of environmental microbiology at Caltech who, in partnership with postdoctoral scholar Hang Yu, explained the findings in the July 16 issue of the journal Nature. “A wonderful aspect of microbes in nature is that they can metabolize seemingly unlikely materials, like metals, yielding energy useful to the cell.”
The study also highlights that the bacteria has the ability to convert manganese to carbon dioxide into biomass, a process called chemosynthesis. Earlier researchers knew of bacteria and fungi that could oxidize manganese, or strip it of electrons, but they had only speculated that yet-to-be-identified microbes might be able to harness the process to drive growth.
“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 coating was in fact oxidized manganese generated by newfound bacteria that had likely come from the tap water itself. “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 says.
Manganese is one of the most abundant elements on the surface of the earth. Manganese oxides is a dark, clumpy substance and are common in nature; they are found in the subsurface deposits and can also create water-distribution systems.
“There is a whole set of environmental engineering literature on drinking-water-distribution systems getting clogged by manganese oxides,” says Leadbetter. “Clearly, many scientists have considered that bacteria using manganese for energy might be responsible, but evidence supporting this idea was not available until now.”
The research findings can also expand the understanding manganese nodules that dot much of the seafloor. The finding helps researchers to have a better understanding of the geochemistry of groundwater. The bacteria can degrade pollutants in groundwater, a process called bioremediation. By this, several key organisms will “reduce” manganese oxide, which means they donate electrons to it, in a manner similar to how humans use oxygen in the air. Scientists have wondered 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 findings helped to understand manganese nodules that dot much of the seafloor. These round metallic balls, which can be as large as grapefruit, were known to marine researchers as early as the cruises of the HMS Challenger in the 1870s. Since then, such nodules have been found to line the bottom of many of Earth’s oceans. In recent years, mining companies have been making plans to harvest and exploit these nodules, because rare metals are often found concentrated within them.”This underscores the need to better understand marine manganese nodules before they are decimated by mining,” says Yu.
“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 part of this study. “This underscores the need to better understand marine manganese nodules before they are decimated by mining,” says Yu.