Agostino Valeria, Lenic Annika, Bardl Bettina, Rizzotto Valentina, Phan An N T, Blank Lars M, Rosenbaum Miriam A
Institute of Applied Microbiology (iAMB), Aachen Biology and Biotechnology, RWTH Aachen University, Aachen, Germany.
Bio Pilot Plant, Leibniz Institute for Natural Product Research and Infection Biology - Hans Knöll Institute, Jena, Germany.
Front Bioeng Biotechnol. 2020 May 19;8:457. doi: 10.3389/fbioe.2020.00457. eCollection 2020.
Electroautotrophy is a novel and fascinating microbial metabolism, with tremendous potential for CO storage and valorization into chemicals and materials made thereof. Research attention has been devoted toward the characterization of acetogenic and methanogenic electroautotrophs. In contrast, here we characterize the electrophysiology of a sulfate-reducing bacterium, , harboring the Wood-Ljungdahl pathway and, thus, capable of fixing CO into acetyl-CoA. For most electroautotrophs the mode of electron uptake is still not fully clarified. Our electrochemical experiments at different polarization conditions and Fe corrosion tests point to a H- mediated electron uptake ability of this strain. This observation is in line with the lack of outer membrane and periplasmic multi-heme -type cytochromes in this bacterium. Maximum planktonic biomass production and a maximum sulfate reduction rate of 2 ± 0.4 mM day were obtained with an applied cathode potential of -900 mV vs. Ag/AgCl, resulting in an electron recovery in sulfate reduction of 37 ± 1.4%. Anaerobic sulfate respiration is more thermodynamically favorable than acetogenesis. Nevertheless, strains adapted to sulfate-limiting conditions, could be tuned to electrosynthetic production of up to 8 mM of acetate, which compares well with other electroacetogens. The yield per biomass was very similar to H/CO based acetogenesis. Acetate bioelectrosynthesis was confirmed through stable isotope labeling experiments with Na-HCO. Our results highlight a great influence of the CO feeding strategy and start-up H level in the catholyte on planktonic biomass growth and acetate production. In serum bottles experiments, also generated butyrate, which makes even more attractive for bioelectrosynthesis application. A further optimization of these physiological pathways is needed to obtain electrosynthetic butyrate production in biocathodes. This study expands the diversity of facultative autotrophs able to perform H-mediated extracellular electron uptake in Bioelectrochemical Systems (BES). We characterized a sulfate-reducing and acetogenic bacterium, , able to naturally produce acetate and butyrate from CO and H. For any future bioprocess, the exploitation of planktonic growing electroautotrophs with H-mediated electron uptake would allow for a better use of the entire liquid volume of the cathodic reactor and, thus, higher productivities and product yields from CO-rich waste gas streams.
电自养是一种新颖且迷人的微生物代谢方式，在将二氧化碳储存并转化为化学品及由其制成的材料方面具有巨大潜力。研究重点一直集中在产乙酸和产甲烷电自养微生物的特性研究上。相比之下，我们在此描述了一种硫酸盐还原菌的电生理学特性，该菌具有伍德 - 隆达尔途径，因此能够将二氧化碳固定为乙酰辅酶A。对于大多数电自养微生物而言，其电子摄取模式仍未完全阐明。我们在不同极化条件下进行的电化学实验以及铁腐蚀试验表明，该菌株具有通过氢介导的电子摄取能力。这一观察结果与该细菌缺乏外膜和周质多血红素型细胞色素的情况相符。在相对于银/氯化银施加 -900 mV 的阴极电位时，获得了最大的浮游生物量产量以及 2±0.4 mM/天的最大硫酸盐还原速率，这使得硫酸盐还原过程中的电子回收率达到 37±1.4%。厌氧硫酸盐呼吸在热力学上比产乙酸更有利。然而，适应硫酸盐限制条件的菌株可被调控以实现高达 8 mM 乙酸盐的电合成生产，这与其他电产乙酸菌相比具有优势。每生物量的产量与基于氢气/二氧化碳的产乙酸过程非常相似。通过用碳酸氢钠进行稳定同位素标记实验证实了乙酸盐的生物电合成。我们的结果突出了二氧化碳供给策略以及阴极电解液中起始氢气水平对浮游生物量生长和乙酸盐生产的重大影响。在血清瓶实验中，该菌株还产生了丁酸盐，这使得其在生物电合成应用中更具吸引力。需要对这些生理途径进行进一步优化，以在该生物阴极中实现电合成丁酸盐的生产。本研究扩展了能够在生物电化学系统（BES）中通过氢介导进行细胞外电子摄取的兼性自养微生物的多样性。我们描述了一种硫酸盐还原兼产乙酸的细菌，该菌能够从二氧化碳和氢气中自然产生乙酸盐和丁酸盐。对于任何未来的生物过程而言，利用具有氢介导电子摄取能力的浮游生长电自养微生物将能够更好地利用阴极反应器的整个液体体积，从而提高来自富含二氧化碳废气流的生产力和产物产量。
