Bacteria with a metal diet discovered in dirty glassware
Finding ends a century-long search for microbes that live on manganese


Date:
July 15, 2020
Source:
California Institute of Technology
Summary:
Newfound bacteria that oxidize manganese help explain the
geochemistry of groundwater.



FULL STORY ========================================================================== Caltech microbiologists have discovered bacteria that feed on manganese
and use the metal as their source of calories. Such microbes were
predicted to exist over a century ago, but none had been found or
described until now.


========================================================================== "These are the first bacteria found to use manganese as their source of
fuel," says Jared Leadbetter, professor of environmental microbiology
at Caltech who, in collaboration with postdoctoral scholar Hang Yu,
describes 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 reveals that the bacteria can use
manganese to convert carbon dioxide into biomass, a process called chemosynthesis. Previously, 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.

Leadbetter found the bacteria serendipitously after performing unrelated experiments using a light, chalk-like form of manganese. He had left a
glass jar soiled with the substance to soak in tap water in his Caltech
office sink before departing for several months to work off campus. When
he returned, 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 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 take the form of a dark, clumpy substance and are common
in nature; they have been found in subsurface deposits and can also form
in water- distribution systems.

"There is a whole set of environmental engineering literature on drinking- water-distribution systems getting clogged by manganese oxides," says 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." The finding helps researchers better understand the geochemistry of groundwater. It is
known that bacteria can degrade pollutants in groundwater, a process
called bioremediation. When doing 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 also have possible relevance to understanding
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.

But little is understood about how the nodules form in the first place. Yu
and Leadbetter now wonder if microbes similar to what they have found
in freshwater might play a role and they plan to further investigate
the mystery. "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 involved with the study.


========================================================================== Story Source: Materials provided by
California_Institute_of_Technology. Original written by Whitney
Clavin. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Hang Yu, Jared R. Leadbetter. Bacterial chemolithoautotrophy via
manganese oxidation. Nature, 2020; 583 (7816): 453 DOI:
10.1038/s41586- 020-2468-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200715142337.htm

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