Mighty powerful microbes: New insights into microbes that breathe rocks


Date:
February 1, 2022
Source:
Harvard University, Department of Organismic and Evolutionary
Biology
Summary:
Microbes may be miniscule, but they have a massive impact on Earth
and its habitability. They are uniquely different from animals,
plants, and other eukaryotic organisms in that they can gain
energy from 'breathing' a surprisingly wide range of surfaces and
materials. Microbes also drastically re-shape their environment
as they feast on these energy sources, making microbes major
players in the cycling and availability of nutrients on Earth. One
especially well-known example was the rise of oxygen on Earth due
to the metabolism of photosynthetic bacteria.



FULL STORY ========================================================================== Microbes may be miniscule, but they have a massive impact on Earth and
its habitability. They are uniquely different from animals, plants, and
other eukaryotic organisms in that they can gain energy from "breathing"
a surprisingly wide range of surfaces and materials. Microbes also
drastically re-shape their environment as they feast on these energy
sources, making microbes major players in the cycling and availability
of nutrients on Earth.

One especially well-known example was the rise of oxygen on Earth due
to the metabolism of photosynthetic bacteria.


==========================================================================
In more recent years, scientists have discovered an astonishing new
process by which microbes can "breathe" rocks through a process called extracellular electron transfer (EET). With EET microbes are able to
"breathe" rocks and other materials that are outside their cell. In
other words, microbes literally establish an electrical connection to
the outside world, a connection they use to generate the power they
need to grow. Researchers have since found ground- breaking uses for EET-capable microbes, such as aiding in toxic waste cleanup and as a
source of alternative energy.

In a new study in mBio researchers from Harvard and the University of
Minnesota surveyed the tree of life in search of EET and discovered
it is far more widespread than previously thought and is spread through horizontal gene transfer. One set of genes that makes EET possible, called mtrCAB, have been especially well-studied in the bacterium Shewanella oneidensis. Shewanella oneidensis was one of the first EET-capable
organisms ever discovered. As such, it's had a decades-long head start
for the science community to interrogate it in the lab.

"A lot of our understanding of mtrCAB comes from studies in this
particular organism," said co-lead author Isabel R. Baker, PhD candidate
in the Department of Organismic and Evolutionary Biology at Harvard. "But
we don't really know how widespread this type of metabolism is amongst
all of life's branches.

Understanding how widespread it is will help us pinpoint where this kind
of metabolism is at play in global biogeochemical cycles." Baker and
co-senior author Professor Peter R. Girgus, also in the Department of Organismic and Evolutionary Biology at Harvard, were keen on partnering
with University of Minnesota researchers co-senior author Professor
Jeffrey A.

Gralnick and co-lead author Bridget E. Conley. Gralnick and Conley are
leading experts in EET research in Shewanella. Their previous work found
that mtrCAB enables EET in at least two other species beyond Shewanella.

In combining their expertise and a global database, the researchers
found that these genes existed in far more organisms than previously
assumed and in a wide variety of environments all over the world.

"We found these genes in microbes all over the planet from virtually every
kind of environment, including the deep sea, salt flats, oil refinery
sites, the human gut, and even wastewater contaminated by the Manhattan project," Baker said. Further analysis revealed that the set of genes
were horizontally transferred extensively throughout the history of life.

"The acquisition of genes is analogous to installing an app on your
phone to give it a new functionality. Horizontal gene transfer is often associated with antibiotic resistance, but here we see a metabolic
capability, EET, moving in and out of bacterial genomes," Gralnick said.

The researchers hypothesized that whenever the genes landed in different species the genes involved in EET would change over time to better suit
the new organism's physiology and the environment it lives in.

"It's sort of a foregone conclusion that microbes really shape our planet
and EET had always been viewed as a niche ability," Girguis said. "But
we looked at all of the genomic information from animals, Archaea, and bacteria, and all other forms of life and found it's far more widespread
than previously assumed.

All of the organisms we identified are capable of plugging directly into
the substrates in their environment and changing what's available there."
"The availability of these different substrates change over time as
the Earth continues to evolve, either naturally or from human impact,"
Baker said.

"Understanding how these proteins may have coevolved with the
history of oxygen on earth is very important. It could help
us understand if this metabolism, or a metabolism like this,
helped play a role in one of the massive transformations of our
planet's surface that gave rise to the modern world as we know it." ========================================================================== Story Source: Materials provided by Harvard_University,_Department_of_Organismic_and
Evolutionary_Biology. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Isabel R. Baker, Bridget E. Conley, Jeffrey A. Gralnick, Peter R.

Girguis. Evidence for Horizontal and Vertical Transmission of Mtr-
Mediated Extracellular Electron Transfer among the Bacteria. mBio,
2022; DOI: 10.1128/mbio.02904-21 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220201143958.htm

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