DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin, USA.
Wisconsin Energy Institute, University of Wisconsin, Madison, Wisconsin, USA.
mBio. 2024 Aug 14;15(8):e0171824. doi: 10.1128/mbio.01718-24. Epub 2024 Jul 16.
Aromatic compounds are an important source of commodity chemicals traditionally produced from fossil fuels. Aromatics derived from plant lignin can potentially be converted into commodity chemicals through depolymerization followed by microbial funneling of monomers and low molecular weight oligomers. This study investigates the catabolism of the β-5 linked aromatic dimer dehydrodiconiferyl alcohol (DC-A) by the bacterium . We used genome-wide screens to identify candidate genes involved in DC-A catabolism. Subsequent and analyses of these candidate genes elucidated a catabolic pathway composed of four required gene products and several partially redundant dehydrogenases that convert DC-A to aromatic monomers that can be funneled into the central aromatic metabolic pathway of . Specifically, a newly identified γ-formaldehyde lyase, PcfL, opens the phenylcoumaran ring to form a stilbene and formaldehyde. A lignostilbene dioxygenase, LsdD, then cleaves the stilbene to generate the aromatic monomers vanillin and 5-formylferulate (5-FF). We also showed that the aldehyde dehydrogenase FerD oxidizes 5-FF before it is decarboxylated by LigW, yielding ferulic acid. We found that some enzymes involved in the β-5 catabolism pathway can act on multiple substrates and that some steps in the pathway can be mediated by multiple enzymes, providing new insights into the robust flexibility of aromatic catabolism in . A comparative genomic analysis predicted that the newly discovered β-5 aromatic catabolic pathway is common within the order Sphingomonadales.
In the transition to a circular bioeconomy, the plant polymer lignin holds promise as a renewable source of industrially important aromatic chemicals. However, since lignin contains aromatic subunits joined by various chemical linkages, producing single chemical products from this polymer can be challenging. One strategy to overcome this challenge is using microbes to funnel a mixture of lignin-derived aromatics into target chemical products. This approach requires strategies to cleave the major inter-unit linkages of lignin to release monomers for funneling into valuable products. In this study, we report newly discovered aspects of a pathway by which the DSM12444 catabolizes aromatics joined by the second most common inter-unit linkage in lignin, the β-5 linkage. This work advances our knowledge of aromatic catabolic pathways, laying the groundwork for future metabolic engineering of this and other microbes for optimized conversion of lignin into products.
芳香族化合物是传统上从化石燃料中生产商品化学品的重要来源。源自植物木质素的芳烃可以通过解聚，然后微生物对单体和低分子量低聚物进行漏斗化，潜在地转化为商品化学品。本研究调查了细菌对 β-5 连接的芳香二聚体脱氢二松柏醇（DC-A）的分解代谢。我们使用全基因组筛选来鉴定参与 DC-A 分解代谢的候选基因。随后对这些候选基因进行 和 分析，阐明了由四个必需基因产物和几个部分冗余脱氢酶组成的分解代谢途径，这些酶将 DC-A 转化为可被漏斗到 的中心芳香代谢途径的芳香单体。具体而言，新鉴定的γ-甲醛裂解酶 PcfL 打开苯并香豆素环，形成芪和甲醛。木质素芪双加氧酶 LsdD 然后将芪裂解生成芳香单体香草醛和 5-甲酰基阿魏酸（5-FF）。我们还表明，醛脱氢酶 FerD 在 LigW 脱羧前氧化 5-FF，生成阿魏酸。我们发现，β-5 分解代谢途径中的一些酶可以作用于多种底物，并且途径中的一些步骤可以由多种酶介导，这为芳香分解代谢在 中的强大灵活性提供了新的见解。比较基因组分析预测，新发现的 β-5 芳香分解代谢途径在单胞菌目中很常见。
在向循环生物经济的过渡中，植物聚合物木质素有望成为工业上重要芳香化学品的可再生来源。然而，由于木质素包含由各种化学键连接的芳香亚基，因此从该聚合物中生产单一化学产品可能具有挑战性。克服这一挑战的一种策略是利用微生物将木质素衍生的芳烃混合物导向目标化学产物。这种方法需要策略来裂解木质素的主要单元间键以释放用于漏斗到有价值产品的单体。在这项研究中，我们报告了 DSM12444 分解代谢通过第二常见的木质素单元间键，β-5 键连接的芳烃的途径的新发现方面。这项工作增进了我们对芳香分解代谢途径的了解，为未来通过代谢工程优化木质素转化为产品的这和其他微生物奠定了基础。
