Production of adipic acid by the native-occurring pathway in Thermobifida fusca B6

To identify the native‐occurring adipate pathway in a previously engineered Thermobifida fusca B6 strain and optimize the adipic acid production of this strain on glucose and corncob. The native‐occurring adipate pathway in T. fusca B6 was identified to be the reverse adipate degradation pathway, including five steps: β‐ketothiolase (Tfu_0875), 3‐hydroxyacyl‐CoA dehydrogenase (Tfu_2399), 3‐hydroxyadipyl‐CoA dehydrogenase (Tfu_0067), 5‐Carboxy‐2‐pentenoyl‐CoA reductase (Tfu_1647) and succinyl‐CoA synthetase (Tfu_2576, Tfu_2577). The cell lysates of T. fusca wild‐type strain with the addition of the Tfu_1647 protein produced trace adipic acid, while no adipic acid was produced in the absence of this protein. The above results prove that the low expression of Tfu_1647 in the wild‐type strain was the reason why it did not produce any adipic acid. We then demonstrated that in T. fusca B6, the maximal titre of adipic acid on 50 g l−1 glucose was 2·23 g l−1 with 0·045 g g−1‐glucose yield and 0·22 g l−1 adipic acid was produced from 19·38 g l−1 milled corncob. The reverse adipate degradation pathway was found to be responsible for the adipate synthesis in T. fusca B6 and Tfu_1647 was the regulatory node on this pathway. Thermobifida fusca B6 was the first reported micro‐organism using its native‐occurring pathway to accumulate adipic acid. It had the highest reported yield and titre of adipic acid so far.