Developments in lignin degradation: New microorganisms and enzymes at
play

Date:
February 24, 2022
Source:
Tokyo University of Science
Summary:
Lignin, a chief component of cell walls in plants, is naturally
degraded in the soil. Identifying new microorganisms involved in
this degradation can help develop novel lignin breakdown processes
in industrial settings.

Now, researchers have isolated 8 microorganisms that degrade the
lignin model compound 2-phenoxyacetophenone (2-PAP). They found
that one of these microbes uses a new, unidentified enzyme to
cleave the ether-bonds in 2-PAP, resulting in the formation of
phenol and benzoate.



FULL STORY ========================================================================== Researchers isolate 8 new types of microorganisms that cleave ether
bonds in the lignin-based compound -- 2-phenoxyacetophenone.


========================================================================== Lignin, a chief component of cell walls in plants, is naturally
degraded in the soil. Identifying new microorganisms involved in
this degradation can help develop novel lignin breakdown processes in industrial settings. Now, researchers from Tokyo University of Science
have isolated 8 microorganisms that degrade the lignin model compound 2-phenoxyacetophenone (2-PAP). They found that one of these microbes
uses a new, unidentified enzyme to cleave the ether-bonds in 2-PAP,
resulting in the formation of phenol and benzoate.

Like all known life forms, plants have a body made of organic matter,
including cell walls made of various components including lignin,
a heterogenous polymer.

Lignin is the second-most abundant organic substance on earth with great potential in the production of industrial chemicals, such as aromatic compounds.

Chemically, lignin is made up of multiple subunits linked by 'ether'
and 'carbon-carbon' bonds, all of which need to be broken down for
lignin decay. It is well known that microorganisms cleave ether bonds effectively through the production of extracellular enzymes, which aid
in lignin degradation. Two microbes that perform this degradation were identified: white-rot fungi through the production of peroxidases and
laccases and Sphingomonad bacteria with the help of intracellular enzymes.

These discoveries sparked curiosity among a team of researchers
including Dr.

Toshiki Furuya and Ms. Saki Oya from Tokyo University of Science, and Dr.

Hiroshi Habe from National Institute of Advanced Industrial Science
and Technology in Tokyo, on whether there are additional, unknown microorganisms that degrade lignin through different enzymes. Identifying
these microorganisms and finding out how they degrade lignin could
enhance the overall understanding of the carbon cycle and facilitate
the biotechnological applications of these microorganisms for lignin commercialization. The team also realized that none of the previous
studies have focused on how microorganisms transform or degrade 2-PAP.

To find an answer to these questions, Dr. Furuya and his team conducted
a study, published in Scientific Reports to screen microorganisms that
utilize new ether-bond cleaving enzymes, to transform 2-PAP. The team
initially used a direct screening method to isolate microorganisms from
soil based on their ether-bond cleaving activity, by growing them on
a medium containing humic acid, a soil-derived organic compound, as a
carbon source. Next, they incubated the isolated microorganisms with
2-PAP to check specifically for 2-PAP ether bond-cleaving activity. The
bond cleaving activity was confirmed depending on the presence of phenol,
which is generally produced as a result of ether-bond cleavage.

This led to the isolation of not one, but eight 2-PAP-transforming microorganisms! These included 7 bacteria from the genus Acinetobacter, Cupriavidus, Nocardioides, and Streptomyces, and 1 fungus from the
genus Penicillium. "To our knowledge, these are the first microorganisms demonstrated to cleave the ether bond of 2-PAP," Dr. Furuya emphasized,
when asked about these discoveries.

Among the isolated microorganisms, the team examined a gram-negative
bacterium, Acinetobacter sp. TUS-SO1 in detail and discovered that
it selectively and oxidatively cleaves ether bonds in 2-PAP, to
produce phenol and benzoate. This was especially surprising, because b-etherase, a well-studied enzyme known to perform this cleaving,
gives phenol and acetophenone. This implies that this bacterial
strain cleaves the ether-bond of 2-PAP using an unidentified enzyme!
When asked about the implications of these findings, Dr. Furuya says,
"These newly identified microorganisms might play important roles in
the degradation of lignin-based compounds in nature. By clarifying the properties of these microorganisms, we can apply them to lignin-based
compounds for the generation of aromatic compounds, as an alternative
to petroleum. Moreover, they can be utilized for lignin valorization, especially for the conversion of low- molecular-weight compounds that
have chemical structures similar to 2-PAP." How is the technique
for the identification of lignin-degrading microorganisms useful in
the long-run? Well, according to the authors, this established search technology can be widely applied to search for microorganisms that exhibit cleavage activity against other ether compounds, such as environmental pollutants.

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


========================================================================== Journal Reference:
1. Saki Oya, Satoshi Tonegawa, Hirari Nakagawa, Hiroshi Habe, Toshiki
Furuya. Isolation and characterization of microorganisms capable
of cleaving the ether bond of 2-phenoxyacetophenone. Scientific
Reports, 2022; 12 (1) DOI: 10.1038/s41598-022-06816-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220224112630.htm

--- up 11 weeks, 5 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)