Herbicide-resistance in weeds has become a serious threat to agriculture across the world. Thus, there is an urgent need for the discovery and development of herbicides with new modes of action. Thaxtomin phytotoxins are a group of nitrated diketopiperazines produced by potato common scab-causing phytopathogen Streptomyces scabies and other actinobacterial pathogens. They are generally considered to function as inhibitors of cellulose synthesis in plants, and thus have great potential to be used as natural herbicides. Generation of an overproducing strain is crucial for the scale-up production of thaxtomins and their wide use in agriculture. In the present study, we employed a stepwise strategy by combining heterologous expression, repressor deletion, activator overexpression, and optimization of fermentation media for high-level production of thaxtomins. The maximum yield of 728 mg/L thaxtomins was achieved with engineered Streptomyces albidoflavus J1074 strains in shake-flask cultures, and it was approximately 36-fold higher than S. albidoflavus J1074 carrying the unmodified cluster. Moreover, the yield of thaxtomins could reach 1973 mg/L when the engineered strain was cultivated in a small-scale stirred-tank bioreactor. This is the highest titer reported to date, representing a significant leap forward for the scale-up production of thaxtomins. Our study presents a robust, easy-to-use system that will be broadly useful for improving titers of bioactive compounds in many Streptomyces species.

杂草中的除草剂抗性已成为全球农业的严重威胁。因此，迫切需要发现和开发具有新作用方式的除草剂。Thaxtomin 植物毒素是一组硝化的二酮哌嗪，由马铃薯常见的结痂植物病原体链霉菌疥疮产生和其他放线菌病原体。它们通常被认为是植物中纤维素合成的抑制剂，因此具有用作天然除草剂的巨大潜力。产生过度生产的菌株对于 thaxtomin 的扩大生产及其在农业中的广泛应用至关重要。在本研究中，我们采用了一种逐步策略，通过结合异源表达、阻遏物缺失、激活剂过表达和发酵培养基的优化来实现 thaxtomin 的高水平生产。在摇瓶培养中使用工程化的Streptomyces albidoflavus J1074 菌株获得了 728 mg/L thaxtomin 的最大产量，比S. albidoflavus高出约 36 倍J1074 携带未修改的集群。此外，将工程菌株在小型搅拌釜生物反应器中培养时，thaxtomin的产量可达1973 mg/L。这是迄今为止报道的最高滴度，代表了 thaxtomin 扩大生产的重大飞跃。我们的研究提出了一个强大、易于使用的系统，该系统将广泛用于提高许多链霉菌属物种中生物活性化合物的滴度。