Terragia Biofuel Incorporated, Hanover, New Hampshire, United States.
Dartmouth College, Thayer School of Engineering, Hanover, New Hampshire, United States.
Sci Rep. 2023 Feb 10;13(1):2394. doi: 10.1038/s41598-023-29220-9.
Cocultures of engineered thermophilic bacteria can ferment lignocellulose without costly pretreatment or added enzymes, an ability that can be exploited for low cost biofuel production from renewable feedstocks. The hemicellulose-fermenting species Thermoanaerobacterium thermosaccharolyticum was engineered for high ethanol yield, but we found that the strains switched from growth-coupled production of ethanol to growth uncoupled production of acetate and 1,2-propanediol upon growth cessation, producing up to 6.7 g/L 1,2-propanediol from 60 g/L cellobiose. The unique capability of this species to make 1,2-propanediol from sugars was described decades ago, but the genes responsible were not identified. Here we deleted genes encoding methylglyoxal reductase, methylglyoxal synthase and glycerol dehydrogenase. Deletion of the latter two genes eliminated propanediol production. To understand how carbon flux is redirected in this species, we hypothesized that high ATP levels during growth cessation downregulate the activity of alcohol and aldehyde dehydrogenase activities. Measurements with cell free extracts show approximately twofold and tenfold inhibition of these activities by 10 mM ATP, supporting the hypothesized mechanism of metabolic redirection. This result may have implications for efforts to direct and maximize flux through alcohol dehydrogenase in other species.
共培养工程嗜热菌可以在无需昂贵的预处理或添加酶的情况下发酵木质纤维素，这种能力可用于从可再生原料生产低成本生物燃料。产乙醇的半纤维素发酵物种热解纤维梭菌经过工程改造以提高乙醇产量，但我们发现，当菌株停止生长时，它们会从生长偶联的乙醇生产转变为生长解偶联的乙酸和 1,2-丙二醇生产，从 60g/L 的纤维二糖生产高达 6.7g/L 的 1,2-丙二醇。该物种具有从糖中生产 1,2-丙二醇的独特能力，这一能力几十年前就已被描述，但负责这一能力的基因尚未被鉴定。在这里，我们删除了编码甲基乙二醛还原酶、甲基乙二醛合酶和甘油脱氢酶的基因。删除后两个基因消除了丙二醇的生产。为了了解该物种如何重新定向碳通量，我们假设生长停止时高 ATP 水平下调了醇和醛脱氢酶活性。用无细胞提取物进行的测量表明，10mM ATP 对这些活性的抑制作用约为两倍和十倍，支持代谢重定向的假设机制。这一结果可能对努力指导和最大化其他物种中醇脱氢酶的通量具有重要意义。
