Liu Defei, Zhang Yongli, Li Jingen, Sun Wenliang, Yao Yonghong, Tian Chaoguang
Key Laboratory of Engineering Biology for Low-carbon Manufacturing, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308, China.
National Technology Innovation Center of Synthetic Biology, Tianjin, 300308, China.
Biotechnol Biofuels Bioprod. 2023 Jan 23;16(1):13. doi: 10.1186/s13068-023-02266-7.
With D-xylose being the second most abundant sugar in nature, its conversion into products could significantly improve biomass-based process economy. There are two well-studied phosphorylative pathways for D-xylose metabolism. One is isomerase pathway mainly found in bacteria, and the other one is oxo-reductive pathway that always exists in fungi. Except for these two pathways, there are also non-phosphorylative pathways named xylose oxidative pathways and they have several advantages over traditional phosphorylative pathways. In Myceliophthora thermophila, D-xylose can be metabolized through oxo-reductive pathway after plant biomass degradation. The survey of non-phosphorylative pathways in this filamentous fungus will offer a potential way for carbon-efficient production of fuels and chemicals using D-xylose.
In this study, an alternative for utilization of D-xylose, the non-phosphorylative Weimberg pathway was established in M. thermophila. Growth on D-xylose of strains whose D-xylose reductase gene was disrupted, was restored after overexpression of the entire Weimberg pathway. During the construction, a native D-xylose dehydrogenase with highest activity in M. thermophila was discovered. Here, M. thermophila was also engineered to produce 1,2,4-butanetriol using D-xylose through non-phosphorylative pathway. Afterwards, transcriptome analysis revealed that the D-xylose dehydrogenase gene was obviously upregulated after deletion of D-xylose reductase gene when cultured in a D-xylose medium. Besides, genes involved in growth were enriched in strains containing the Weimberg pathway.
The Weimberg pathway was established in M. thermophila to support its growth with D-xylose being the sole carbon source. Besides, M. thermophila was engineered to produce 1,2,4-butanetriol using D-xylose through non-phosphorylative pathway. To our knowledge, this is the first report of non-phosphorylative pathway recombinant in filamentous fungi, which shows great potential to convert D-xylose to valuable chemicals.
D-木糖是自然界中含量第二丰富的糖类，将其转化为产品可显著提高基于生物质的工艺经济性。D-木糖代谢存在两条经过充分研究的磷酸化途径。一条是主要存在于细菌中的异构酶途径，另一条是真菌中普遍存在的氧化还原途径。除了这两条途径外，还存在名为木糖氧化途径的非磷酸化途径，它们相对于传统的磷酸化途径具有若干优势。在嗜热毁丝霉中，植物生物质降解后，D-木糖可通过氧化还原途径进行代谢。对这种丝状真菌中非磷酸化途径的研究将为利用D-木糖高效生产燃料和化学品提供一条潜在途径。
在本研究中，在嗜热毁丝霉中建立了利用D-木糖的另一种途径，即非磷酸化的温伯格途径。D-木糖还原酶基因被破坏的菌株在D-木糖上的生长，在整个温伯格途径过表达后得以恢复。在构建过程中，发现了嗜热毁丝霉中活性最高的天然D-木糖脱氢酶。在此，还对嗜热毁丝霉进行了工程改造，使其通过非磷酸化途径利用D-木糖生产1,2,4-丁三醇。随后，转录组分析表明，在D-木糖培养基中培养时，D-木糖还原酶基因缺失后，D-木糖脱氢酶基因明显上调。此外，含有温伯格途径的菌株中与生长相关的基因得到了富集。
在嗜热毁丝霉中建立了温伯格途径，以支持其以D-木糖作为唯一碳源生长。此外，对嗜热毁丝霉进行了工程改造，使其通过非磷酸化途径利用D-木糖生产1,2,4-丁三醇。据我们所知，这是丝状真菌中非磷酸化途径重组的首次报道，显示出将D-木糖转化为有价值化学品的巨大潜力。
