Institute of Molecular Biology and Biotechnology of Prokaryotes, University of Ulm, Ulm, Germany.
Institute of Bioprocess and Biosystems Engineering, Hamburg University of Technology, Hamburg, Germany.
Microb Cell Fact. 2024 Jul 26;23(1):213. doi: 10.1186/s12934-024-02481-3.
Acetogens, a diverse group of anaerobic autotrophic bacteria, are promising whole-cell biocatalysts that fix CO during their growth. However, because of energetic constraints, acetogens exhibit slow growth and the product spectrum is often limited to acetate. Enabling acetogens to form more valuable products such as volatile fatty acids during autotrophic growth is imperative for cementing their place in the future carbon neutral industry. Co-cultivation of strains with different capabilities has the potential to ease the limiting energetic constraints. The lactate-mediated co-culture of an Acetobacterium woodii mutant strain, capable of lactate production, with the Clostridium drakei SL1 type strain can produce butyrate and hexanoate. In this study, the preceding co-culture is characterized by comparison of monocultures and different co-culture approaches.
C. drakei grew with H + CO as main carbon and energy source and thrived when further supplemented with D-lactate. Gas phase components and lactate were consumed in a mixotrophic manner with acetate and butyrate as main products and slight accumulation of hexanoate. Formate was periodically produced and eventually consumed by C. drakei. A lactate-mediated co-culture of the A. woodii [P_ldhD_NFP] strain, engineered for autotrophic lactate production, and C. drakei produced up to 4 ± 1.7 mM hexanoate and 18.5 ± 5.8 mM butyrate, quadrupling and doubling the respective titers compared to a non-lactate-mediated co-culture. Further co-cultivation experiments revealed the possible advantage of sequential co-culture over concurrent approaches, where both strains are inoculated simultaneously. Scanning electron microscopy of the strains revealed cell-to-cell contact between the co-culture partners. Finally, a combined pathway of A. woodii [P_ldhD_NFP] and C. drakei for chain-elongation with positive ATP yield is proposed.
Lactate was proven to be a well-suited intermediate to combine the high gas uptake capabilities of A. woodii with the chain-elongation potential of C. drakei. The cell-to-cell contact observed here remains to be further characterized in its nature but hints towards diffusive processes being involved in the co-culture. Furthermore, the metabolic pathways involved are still speculatory for C. drakei and do not fully explain the consumption of formate while H + CO is available. This study exemplifies the potential of combining metabolically engineered and native bacterial strains in a synthetic co-culture.
产乙酸菌是一群多样的厌氧自养细菌，是具有前景的全细胞生物催化剂，在生长过程中固定 CO。然而，由于能量限制，产乙酸菌的生长缓慢，产物谱通常仅限于乙酸盐。使产乙酸菌在自养生长过程中形成更有价值的产物，如挥发性脂肪酸，对于巩固它们在未来碳中和产业中的地位是至关重要的。具有不同能力的菌株的共培养有可能缓解能量限制的问题。具有产乳酸能力的乙酰乙酸木杆菌突变株与 Clostridium drakei SL1 型菌株的乳酸介导共培养可以产生丁酸和己酸。在这项研究中，通过比较单培养和不同共培养方法来对前面的共培养进行了表征。
C. drakei 以 H+CO 作为主要碳源和能源生长，并在进一步补充 D-乳酸时茁壮成长。以混合营养的方式消耗气相成分和乳酸，主要产物为乙酸盐和丁酸盐，少量积累己酸盐。甲酸周期性地产生并最终被 C. drakei 消耗。一株经工程改造用于自养产乳酸的乙酰乙酸木杆菌[A_ldhD_NFP]菌株与 C. drakei 的乳酸介导共培养，可产生高达 4±1.7 mM 的己酸和 18.5±5.8 mM 的丁酸，分别是无乳酸介导共培养的四倍和两倍。进一步的共培养实验表明，顺序共培养优于同时接种两种菌株的共培养方法。扫描电子显微镜观察发现，共培养物中的两种菌株之间存在细胞间接触。最后，提出了一种乙酰乙酸木杆菌[A_ldhD_NFP]和 C. drakei 用于链延伸的组合途径，具有正的 ATP 产率。
乳酸被证明是一种合适的中间产物，可以将乙酰乙酸木杆菌的高气吸收能力与 C. drakei 的链延伸潜力结合起来。这里观察到的细胞间接触有待进一步确定其性质，但暗示共培养物中涉及扩散过程。此外，对于 C. drakei 来说，所涉及的代谢途径仍然是推测性的，并且不能完全解释在有 H+CO 可用的情况下甲酸的消耗。本研究例证了在合成共培养中结合代谢工程改造和天然细菌菌株的潜力。
