Acetic acid-producing bacteria (acetogens) are very
interesting for the biotech industry: They fix the climate gas CO2
and at the same time produce not only acetic acid, but also substances such as
ethanol or – after genetic modification – products such as acetone or
bioplastics. For many years now, microbiologist Volker Müller from Goethe
University has been researching how these bacteria extract energy from CO2
– and has done so very successfully. Now he wants to crack the last puzzle of
this energy production. As part of the renowned Reinhart Koselleck Programme,
the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) is now
funding his project as a particularly innovative and refreshingly risky project.
FRANKFURT. They live in the soil, in sediments of bodies of water and in
other oxygen-free environments: Bacteria known as acetogenic bacteria or
acetogens that produce acetic acid from carbon dioxide (CO2) and
obtain energy through this fermentation process. Phylogenetically, acetogens
are among the oldest species of bacteria on Earth, having evolved more than
three billion years ago, when the Earth's atmosphere was still oxygen-free. In
recent years, the team of microbiologist Professor Volker Müller has partially
elucidated how CO2 reduction is coupled with energy production:
Acetogens have two different respiratory chains with the help of which they
produce the cellular energy currency ATP, either with the central respiratory
enzyme "Rnf" or with "Ech". Usually, a bacterial species
possesses only one of these two respiratory chain types.
However, in addition to the enzymes Rnf or
Ech, some acetogens also possess cytochrome-containing enzymes, which are
central to oxygen respiration in both bacteria and higher cells. Although cytochomes
were discovered in acetogens more than 40 years ago, no one has yet been able
to demonstrate that acetogens – for which contact with oxygen is lethal –
actually use their cytochromes for a form of respiration.
Over the next five years, the team led by
Professor Volker Müller wants to find out what function cytochromes have in
acetogens. The microbiologist explains: "Thanks to our many years of work
on acetogens, we have the best prerequisites for cracking the riddle. These are
very exciting times for us. After all, the cytochrome, which is much more
complex to produce in biosynthesis for the bacterial cell, could actually be
part of a third, oxygen-independent form of respiration. Or it may have a
completely different function, perhaps serving to detoxify molecular oxygen and
keep the bacterium from dying from oxygen."
With their basic research, the scientists
want to prepare the ground for biotechnological applications of acetogenic
bacteria. Currently, for example, 90 percent of the more than 3 million tons of
acetic acid produced worldwide annually is obtained from fossil oil or gas.
Müller: "If you want to use genetically modified acetogens to produce
non-natural compounds such as acetone or bioplastics, you will need to have a sound
understanding of the complex, essential metabolic processes in the bacteria.
This is because the bacteria require a lot of energy for the non-natural
compounds, which the chemical reduction of CO2 provides only to a
limited extent. That is why with our research, we hope to make an important
contribution to understanding energy production in acetogens, thereby opening
the door for more efficient applications."
Professor Volker Müller holds the Chair of
Molecular Microbiology and Bioenergetics at Goethe University's Faculty of
Biological Sciences. He received his PhD in Göttingen, was a postdoctoral
researcher at Yale University, habilitated in microbiology in Göttingen, and
held a C3 professorship in microbiology at LMU Munich before coming to
Frankfurt in 2002. He gained worldwide recognition for his work on the
metabolism of acetogenic bacteria. His projects are funded by the German
Research Foundation DFG and he coordinated a European research consortium on
the application of acetogenic bacteria in industry. Currently, his work on the
physiology and application of acetogenic bacteria is funded by a prestigious
ERC Advanced Grant. With almost 300 publications, Müller is one of the world's
leading researchers in the field of metabolism of anaerobic bacteria and
archaea.
Image
for download: https://www.uni-frankfurt.de/128212374
Caption:
Professor Volker Müller, Goethe University
Frankfurt (Photo: Uwe Dettmar for Goethe University)
Background:
Acetogenic bacterium contains both Rnf and
Ech enzymes (01/2020)
https://aktuelles.uni-frankfurt.de/englisch/new-metabolic-pathway-discovered-in-rumen-microbiome/
Isolation of the Rnf enzyme complex
(08/2020)
https://aktuelles.uni-frankfurt.de/englisch/how-microbes-in-the-primordial-atmosphere-obtained-energy-without-oxygen/
Further information
Professor
Volker Müller
Department of Molecular Microbiology &
Bioenergetics
Institute for Molecular Biosciences
Goethe University Frankfurt
Tel.: +49 (0)69 798-29507
vmueller@bio.uni-frankfurt.de
