Centre of Biological Engineering, University of Minho, Braga, Portugal.
Laboratory of Microbiology, Wageningen University & Research, Wageningen, The Netherlands.
Appl Environ Microbiol. 2021 Jun 25;87(14):e0283920. doi: 10.1128/AEM.02839-20.
Gas fermentation is a promising way to convert CO-rich gases to chemicals. We studied the use of synthetic cocultures composed of carboxydotrophic and propionigenic bacteria to convert CO to propionate. So far, isolated carboxydotrophs cannot directly ferment CO to propionate, and therefore, this cocultivation approach was investigated. Four distinct synthetic cocultures were constructed, consisting of Acetobacterium wieringae (DSM 1911) and Pelobacter propionicus (DSM 2379), (DSM 1911) and Anaerotignum neopropionicum (DSM 3847), strain JM and (DSM 2379), and strain JM and (DSM 3847). Propionate was produced by all the cocultures, with the highest titer (∼24 mM) being measured in the coculture composed of strain JM and , which also produced isovalerate (∼4 mM), butyrate (∼1 mM), and isobutyrate (0.3 mM). This coculture was further studied using proteogenomics. As expected, enzymes involved in the Wood-Ljungdahl pathway in strain JM, which are responsible for the conversion of CO to ethanol and acetate, were detected; the proteome of confirmed the conversion of ethanol to propionate via the acrylate pathway. In addition, proteins related to amino acid metabolism and stress response were highly abundant during cocultivation, which raises the hypothesis that amino acids are exchanged by the two microorganisms, accompanied by isovalerate and isobutyrate production. This highlights the importance of explicitly looking at fortuitous microbial interactions during cocultivation to fully understand coculture behavior. Syngas fermentation has great potential for the sustainable production of chemicals from wastes (via prior gasification) and flue gases containing CO/CO. Research efforts need to be directed toward expanding the product portfolio of gas fermentation, which is currently limited to mainly acetate and ethanol. This study provides the basis for a microbial process to produce propionate from CO using synthetic cocultures composed of acetogenic and propionigenic bacteria and elucidates the metabolic pathways involved. Furthermore, based on proteomics results, we hypothesize that the two bacterial species engage in an interaction that results in amino acid exchange, which subsequently promotes isovalerate and isobutyrate production. These findings provide a new understanding of gas fermentation and a coculturing strategy for expanding the product spectrum of microbial conversion of CO/CO.
气体发酵是将富 CO 气体转化为化学品的一种很有前途的方法。我们研究了利用由产羧菌和丙酸菌组成的合成共培养物将 CO 转化为丙酸盐。到目前为止，分离出的产羧菌不能直接将 CO 发酵为丙酸盐，因此研究了这种共培养方法。构建了四个不同的合成共培养物，由醋酸杆菌（DSM 1911）和丙酸丙酸杆菌（DSM 2379）组成，醋酸杆菌（DSM 1911）和厌氧丙酸杆菌（DSM 3847）组成，菌株 JM 和丙酸丙酸杆菌（DSM 2379）组成，以及菌株 JM 和厌氧丙酸杆菌（DSM 3847）组成。所有共培养物均产生丙酸盐，其中由菌株 JM 和厌氧丙酸杆菌（DSM 3847）组成的共培养物的浓度最高（约 24 mM），同时还产生异戊酸盐（约 4 mM）、丁酸盐（约 1 mM）和异丁酸盐（0.3 mM）。进一步利用蛋白质组学研究了该共培养物。正如预期的那样，在菌株 JM 中检测到了参与 Wood-Ljungdahl 途径的酶，该途径负责将 CO 转化为乙醇和乙酸；在 中鉴定到的蛋白质证实了通过丙烯酸盐途径将乙醇转化为丙酸盐。此外，共培养过程中氨基酸代谢和应激反应相关的蛋白质含量很高，这提出了一个假设，即两种微生物通过交换氨基酸，并伴随着异戊酸盐和异丁酸盐的产生。这突出表明，在共培养过程中明确观察偶然的微生物相互作用对于充分理解共培养行为非常重要。合成气发酵具有从废物（通过预先气化）和含 CO/CO 的烟道气中可持续生产化学品的巨大潜力。研究工作需要致力于扩大气体发酵的产品组合，目前该产品组合主要限于乙酸盐和乙醇。本研究为使用由产乙酸菌和产丙酸菌组成的合成共培养物从 CO 生产丙酸盐提供了基础，并阐明了所涉及的代谢途径。此外，根据蛋白质组学结果，我们假设两种细菌物种之间存在相互作用，导致氨基酸交换，进而促进异戊酸盐和异丁酸盐的产生。这些发现为气体发酵和扩大 CO/CO 微生物转化的产物谱的共培养策略提供了新的认识。
