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Pink-pigmented facultative methylotrophs have long been studied for their ability to grow on reduced single-carbon (C 1 ) compounds. The C 1 groups that support methylotrophic growth may come from a variety of sources. Here, we describe a group of Methylobacterium strains that can engage in methoxydotrophy: they can metabolize the methoxy groups from several aromatic compounds that are commonly the product of lignin depolymerization. Furthermore, these organisms can utilize the full aromatic ring as a growth substrate, a phenotype that has rarely been described in Methylobacterium . We demonstrated growth on p -hydroxybenzoate, protocatechuate, vanillate, and ferulate in laboratory culture conditions. We also used comparative genomics to explore the evolutionary history of this trait, finding that the capacity for aromatic catabolism is likely ancestral to two clades of Methylobacterium , but has also been acquired horizontally by closely related organisms. In addition, we surveyed the published metagenome data to find that the most abundant group of aromatic-degrading Methylobacterium in the environment is likely the group related to Methylobacterium nodulans , and they are especially common in soil and root environments. The demethoxylation of lignin-derived aromatic monomers in aerobic environments releases formaldehyde, a metabolite that is a potent cellular toxin but that is also a growth substrate for methylotrophs. We found that, whereas some known lignin-degrading organisms excrete formaldehyde as a byproduct during growth on vanillate, Methylobacterium do not. This observation is especially relevant to our understanding of the ecology and the bioengineering of lignin degradation.
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5–5 Lignin Linkage Cleavage over Ru: A Density Functional Theory Study
Lignin is the most abundant natural, aromatic-containing biopolymer. Among all the C–C and C–O bonds being cleaved in catalytic fractionation, the 5–5 linkage is the strongest, and its scission requires harsh conditions. Theoretical investigations of the mechanism and kinetics could provide insights into developing better catalysts but are essentially lacking. We perform extensive density functional theory calculations on 2-methoxy-1,1′-biphenyl, a model compound, with various substitutions at all ring locations on Ru(0001). We analyze the competition between the 5–5 bond cleavage and the defunctionalization of the side functional groups at multiple degrees of depolymerization. The role of ring functional groups in the adsorption of lignin oligomers and the 5–5 bond scission and, conversely, the effect of the aromatic group on the −OCH3 decomposition are also discussed. We show that increasing the number of methoxy groups decreases the C–C barrier, and thus, we expect the following depolymerization ranking: grass > softwood > hardwood. While Ru exposes modest 5–5 bond scission reaction barriers from some intermediates, rapid side group chemistry prevents the formation of these intermediates; instead, scission happens most probably from defunctionalized compounds whose C–C scission barriers are high. Our results also expose the existence of multiple Brønsted–Evans–Polanyi relations in the catalytic transformation of biphenyl-based molecules that open up the possibility of modeling depolymerization of large lignin chains.
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- Award ID(s):
- 1934887
- PAR ID:
- 10542958
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- ACS Sustainable Chemistry & Engineering
- Volume:
- 9
- Issue:
- 48
- ISSN:
- 2168-0485
- Page Range / eLocation ID:
- 16143 to 16152
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acssuschemeng.1c04838
