Meriläinen Ella, Efimova Elena, Santala Ville, Santala Suvi
Faculty of Engineering and Natural Sciences, Tampere University, Hervanta Campus, Korkeakoulunkatu 8, 33720, Tampere, Finland.
Biotechnol Biofuels Bioprod. 2024 Jun 8;17(1):78. doi: 10.1186/s13068-024-02526-0.
Lignin is a highly abundant but strongly underutilized natural resource that could serve as a sustainable feedstock for producing chemicals by microbial cell factories. Because of the heterogeneous nature of the lignin feedstocks, the biological upgrading of lignin relying on the metabolic routes of aerobic bacteria is currently considered as the most promising approach. However, the limited substrate range and the inefficient catabolism of the production hosts hinder the upgrading of lignin-related aromatics. Particularly, the aerobic O-demethylation of the methoxyl groups in aromatic substrates is energy-limited, inhibits growth, and results in carbon loss in the form of CO.
In this study, we present a novel approach for carbon-wise utilization of lignin-related aromatics by the integration of anaerobic and aerobic metabolisms. In practice, we employed an acetogenic bacterium Acetobacterium woodii for anaerobic O-demethylation of aromatic compounds, which distinctively differs from the aerobic O-demethylation; in the process, the carbon from the methoxyl groups is fixed together with CO to form acetate, while the aromatic ring remains unchanged. These accessible end-metabolites were then utilized by an aerobic bacterium Acinetobacter baylyi ADP1. By utilizing this cocultivation approach, we demonstrated an upgrading of guaiacol, an abundant but inaccessible substrate to most microbes, into a plastic precursor muconate, with a nearly equimolar yields (0.9 mol/mol in a small-scale cultivation and 1.0 mol/mol in a one-pot bioreactor cultivation). The process required only a minor genetic engineering, namely a single gene knock-out. Noticeably, by employing a metabolic integration of the two bacteria, it was possible to produce biomass and muconate by utilizing only CO and guaiacol as carbon sources.
By the novel approach, we were able to overcome the issues related to aerobic O-demethylation of methoxylated aromatic substrates and demonstrated carbon-wise conversion of lignin-related aromatics to products with yields unattainable by aerobic processes. This study highlights the power of synergistic integration of distinctive metabolic features of bacteria, thus unlocking new opportunities for harnessing microbial cocultures in upgrading challenging feedstocks.
木质素是一种储量丰富但利用程度极低的自然资源，可作为微生物细胞工厂生产化学品的可持续原料。由于木质素原料的异质性，依靠需氧细菌代谢途径对木质素进行生物升级目前被认为是最具前景的方法。然而，生产宿主的底物范围有限以及分解代谢效率低下阻碍了木质素相关芳烃的升级。特别是，芳香族底物中甲氧基的需氧O-去甲基化能量有限，抑制生长，并导致以CO形式的碳损失。
在本研究中，我们提出了一种通过整合厌氧和好氧代谢对木质素相关芳烃进行碳利用的新方法。实际上，我们使用产乙酸细菌伍氏乙酸杆菌对芳香族化合物进行厌氧O-去甲基化，这与需氧O-去甲基化明显不同；在此过程中，甲氧基中的碳与CO一起固定形成乙酸盐，而芳香环保持不变。然后，这些可利用的终产物被需氧细菌拜氏不动杆菌ADP1利用。通过利用这种共培养方法，我们证明了将对大多数微生物来说丰富但难以利用的底物愈创木酚升级为塑料前体粘康酸，产率几乎等摩尔（小规模培养中为0.9 mol/mol，一锅式生物反应器培养中为1.0 mol/mol）。该过程仅需要少量基因工程，即单个基因敲除。值得注意的是，通过采用两种细菌的代谢整合，仅以CO和愈创木酚作为碳源就有可能生产生物质和粘康酸。
通过这种新方法，我们能够克服与甲氧基化芳香族底物的需氧O-去甲基化相关的问题，并证明了木质素相关芳烃向需氧过程无法实现的产率的产物的碳转化。本研究突出了细菌独特代谢特征协同整合的力量，从而为利用微生物共培养升级具有挑战性的原料开辟了新机会。
