Paradigm shift: Methanogenic microbes not always limited to methane


Date:
January 12, 2022
Source:
Technische Universita"t Dresden
Summary:
Microbiologists show that methanogenic archaea do not always
need to form methane to survive. It is possible to bypass
methanogenesis with the seemingly simpler and more environmentally
friendly acetogenic energy metabolism. These new findings provide
evidence that methanogens are not nearly as metabolically limited
as previously thought, and suggest that methanogenesis may have
evolved from the acetyl-CoA pathway - an important step towards
fully understanding the ecology, biotechnology, and evolution
of archaea.



FULL STORY ========================================================================== Archaea are small single-celled microorganisms (microbes) that form
one of the three domains of cellular life, along with bacteria and
eukaryotes. They do not possess a nucleus and therefore belong to the prokaryotes like bacteria.

Methanogenic archaea form methane as the end product of their energy
metabolism (catabolism), an important intermediate product in the global
carbon cycle, which is many times more climate-affecting than carbon
dioxide. Methanogens are found primarily in bogland, rice fields, manure,
and in the digestive tract of ruminants.


========================================================================== Until now, it was considered scientifically established that methanogens
have no alternative means for energy conservation and therefore must
produce methane. The reductive acetyl-coenzyme A (acetyl-CoA) pathway,
which has several steps in common with methanogenesis and is responsible
for the synthesis of cellular components (anabolism) in methanogens,
could represent such an alternative. Indeed, it is the only metabolic
process that can be involved in both catabolism and anabolism.

Prof. Michael Rother, microbiologist at Technische Universita"t Dresden,
and his team, together with colleagues from Go"ttingen, Leipzig and
Helsinki, have now investigated a peculiar phenomenon in the methanogenic archaeon Methanosarcina acetivorans: During growth on carbon monoxide
(CO), M.

acetivorans forms little methane, and cellular carbon flux
is significantly diverted from the methanogenic pathway toward
acetyl-CoA. Acetate produced from the acetyl-CoA pathway directly
allows synthesis of adenosine triphosphate (ATP) through substrate
level phosphorylation.

Rother and his team now wanted to know whether the organism's metabolism
can be completely "forced" into acetogenesis, i.e., whether the
methanogenic traitis indeed essential. The team was successful and ended
up selecting a mutant that grew without significant methane formation,
i.e., that had turned into an acetogen. Genetic, genomic and proteomic
analyses of the selected strain revealed that although crucial components
of the respiratory chain were now absent, the enzyme that produces its substrate (a heterodisulfide) was still essential for survival.

"This apparent contradiction can only be explained by a previously unknown anabolic -- and essential role of the heterodisulfide, which we now need
to figure out," says Prof. Rother, adding, "It is quite something to
overturn such an old paradigm, namely that all methanogens are obligate methanogenic. In fact, they are probably not nearly as limited in energy metabolism as previously thought. Moreover, the possibility of converting methanogenic metabolism into the seemingly simpler acetogenic metabolism suggests that methanogenesis may have evolved from an ancient version
of the acetyl-CoA pathway." If the flexibility of energy metabolism
observed in M. acetivorans is more widespread than previously thought,
it could lead to approaches to reduce human-made methane emissions
without having to completely inhibit these important organisms.

========================================================================== Story Source: Materials provided by Technische_Universita"t_Dresden. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Christian Scho"ne, Anja Poehlein, Nico Jehmlich, Norman Adlung, Rolf
Daniel, Martin von Bergen, Silvan Scheller, Michael Rother.

Deconstructing Methanosarcina acetivorans into an acetogenic
archaeon.

Proceedings of the National Academy of Sciences, 2022; 119 (2):
e2113853119 DOI: 10.1073/pnas.2113853119 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220112105647.htm
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