Kato Junya, Matsuo Takeshi, Takemura Kaisei, Kato Setsu, Fujii Tatsuya, Wada Keisuke, Nakamichi Yusuke, Watanabe Masahiro, Aoi Yoshiteru, Morita Tomotake, Murakami Katsuji, Nakashimada Yutaka
Graduate School of Integrated Sciences for Life, Hiroshima University, 1-3-1 Kagamiyama, Higashihiroshima, Hiroshima, 739-8530, Japan.
National Institute of Advanced Industrial Science and Technology (AIST), 3-11-32 Kagamiyama, Higashihiroshima, Hiroshima, 739-0046, Japan.
Biotechnol Biofuels Bioprod. 2024 Jan 28;17(1):13. doi: 10.1186/s13068-024-02460-1.
Isopropanol (IPA) is a commodity chemical used as a solvent or raw material for polymeric products, such as plastics. Currently, IPA production depends largely on high-CO-emission petrochemical methods that are not sustainable. Therefore, alternative low-CO emission methods are required. IPA bioproduction using biomass or waste gas is a promising method.
Moorella thermoacetica, a thermophilic acetogenic microorganism, was genetically engineered to produce IPA. A metabolic pathway related to acetone reduction was selected, and acetone conversion to IPA was achieved via the heterologous expression of secondary alcohol dehydrogenase (sadh) in the thermophilic bacterium. sadh-expressing strains were combined with acetone-producing strains, to obtain an IPA-producing strain. The strain produced IPA as a major product using hexose and pentose sugars as substrates (81% mol-IPA/mol-sugar). Furthermore, IPA was produced from CO, whereas acetate was an abundant byproduct. Fermentation using syngas containing both CO and H resulted in higher IPA production at the specific rate of 0.03 h. The supply of reducing power for acetone conversion from the gaseous substrates was examined by supplementing acetone to the culture, and the continuous and rapid conversion of acetone to IPA showed a sufficient supply of NADPH for Sadh.
The successful engineering of M. thermoacetica resulted in high IPA production from sugars. M. thermoacetica metabolism showed a high capacity for acetone conversion to IPA in the gaseous substrates, indicating acetone production as the bottleneck in IPA production for further improving the strain. This study provides a platform for IPA production via the metabolic engineering of thermophilic acetogens.
异丙醇（IPA）是一种用作溶剂或聚合物产品（如塑料）原料的商品化学品。目前，IPA的生产在很大程度上依赖于高碳排放的石化方法，这些方法不可持续。因此，需要替代的低碳排放方法。利用生物质或废气进行IPA生物生产是一种很有前景的方法。
嗜热产乙酸微生物热醋穆尔氏菌经过基因工程改造以生产IPA。选择了一条与丙酮还原相关的代谢途径，通过在嗜热细菌中异源表达仲醇脱氢酶（sadh）实现了丙酮向IPA的转化。将表达sadh的菌株与产丙酮菌株组合，获得了一株产IPA的菌株。该菌株以己糖和戊糖为底物，将IPA作为主要产物进行生产（81%摩尔IPA/摩尔糖）。此外，从CO中生产出了IPA，而乙酸是大量的副产物。使用含有CO和H的合成气进行发酵，以0.03 h的比速率实现了更高的IPA产量。通过向培养物中补充丙酮来研究气态底物中丙酮转化所需还原力的供应情况，丙酮持续快速转化为IPA表明为Sadh提供了充足的NADPH。
热醋穆尔氏菌的成功工程改造导致从糖类中高产IPA。热醋穆尔氏菌的代谢在气态底物中显示出将丙酮高效转化为IPA的能力，这表明丙酮生产是IPA生产中的瓶颈，需要进一步改良菌株。本研究为通过嗜热产乙酸菌的代谢工程生产IPA提供了一个平台。
