@inproceedings{EngelThieringerTippkoetter2016,
  author    = {Engel, Mareike and Thieringer, Julia and Tippk{\"o}tter, Nils},
  title     = {Linking bioprocess engineering and electrochemistry for sustainable biofuel production},
  series = {Young Researchers Symposium, YRS 2016. Proceedings},
  booktitle = {Young Researchers Symposium, YRS 2016. Proceedings},
  publisher = {Fraunhofer Verlag},
  address   = {Karlsruhe},
  pages     = {49 -- 53},
  year      = {2016},
  abstract  = {Electromicrobial engineering is an emerging, highly interdisciplinary research area linking bioprocesses with electrochemistry. In this work, microbial electrosynthesis (MES) of biobutanol is carried out during acetone-butanol-ethanol (ABE) fermentations with Clostridium acetobutylicum. A constant electric potential of -600mV (vs. Ag/AgCl) with simultaneous addition of the soluble redox mediator neutral red is used in order to study the electron transfer between the working electrode and the bacterial cells. The results show an earlier initiation of solvent production for all fermentations with applied potential compared to the conventional ABE fermentation. The f inal butanol concentration can be more than doubled by the application of a negative potential combined with addition of neutral red. Moreover a higher biofilm formation on the working electrode compared to control cultivations has been observed. In contrast to previous studies, our results also indicate that direct electron transfer (DET) might be possible with C. acetobutylicum. The presented results make microbial butanol production economically attractive and therefore support the development of sustainable production processes in the chemical industry aspired by the "Centre for resource-efficient chemistry and raw material change" as well as the the project "NanoKat" working on nanostructured catalysts in Kaiserslautern.},
  language  = {en}
}
@article{EngelBayerHoltmannetal.2019,
  author    = {Engel, Mareike and Bayer, Hendrik and Holtmann, Dirk and Tippk{\"o}tter, Nils and Ulber, Roland},
  title     = {Flavin secretion of Clostridium acetobutylicum in a bioelectrochemical system - Is an iron limitation involved?},
  series = {Bioelectrochemistry},
  journal   = {Bioelectrochemistry},
  number    = {In Press, Accepted Manuscript},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1567-5394},
  doi       = {10.1016/j.bioelechem.2019.05.014},
  year      = {2019},
  language  = {en}
}
@article{EngelHoltmannUlberetal.2018,
  author    = {Engel, Mareike and Holtmann, Dirk and Ulber, Roland and Tippk{\"o}tter, Nils},
  title     = {Increased Biobutanol Production by Mediator-Less Electro-Fermentation},
  series = {Biotechnology Journal},
  volume    = {14},
  journal   = {Biotechnology Journal},
  number    = {4},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1860-7314},
  doi       = {10.1002/biot.201800514},
  year      = {2018},
  abstract  = {A future bio-economy should not only be based on renewable raw materials but also in the raise of carbon yields of existing production routes. Microbial electrochemical technologies are gaining increased attention for this purpose. In this study, the electro-fermentative production of biobutanol with C. acetobutylicum without the use of exogenous mediators is investigated regarding the medium composition and the reactor design. It is shown that the use of an optimized synthetic culture medium allows higher product concentrations, increased biofilm formation, and higher conductivities compared to a synthetic medium supplemented with yeast extract. Moreover, the optimization of the reactor system results in a doubling of the maximum product concentrations for fermentation products. When a working electrode is polarized at -600 mV vs. Ag/AgCl, a shift from butyrate to acetone and butanol production is induced. This leads to an increased final solvent yield of Yᴀᴃᴇ = 0.202 gg⁻¹ (control 0.103 gg⁻¹), which is also reflected in a higher carbon efficiency of 37.6\% compared to 23.3\% (control) as well as a fourfold decrease in simplified E-factor to 0.43. The results are promising for further development of biobutanol production in bioelectrochemical systems in order to fulfil the principles of Green Chemistry.},
  language  = {en}
}
@article{EngelGemuendeHoltmannetal.2019,
  author    = {Engel, Mareike and Gem{\"u}nde, Andre and Holtmann, Dirk and M{\"u}ller-Renno, Christine and Ziegler, Christiane and Tippk{\"o}tter, Nils and Ulber, Roland},
  title     = {Clostridium acetobutylicum's connecting world: cell appendage formation in bioelectrochemical systems},
  series = {ChemElectroChem},
  volume    = {7},
  journal   = {ChemElectroChem},
  number    = {2},
  publisher = {Wiley},
  address   = {Weinheim},
  issn      = {2196-0216},
  doi       = {10.1002/celc.201901656},
  pages     = {414 -- 420},
  year      = {2019},
  abstract  = {Bacterial cell appendix formation supports cell-cell interaction, cell adhesion and cell movement. Additionally, in bioelectrochemical systems (BES), cell appendages have been shown to participate in extracellular electron transfer. In this work, the cell appendix formation of Clostridium acetobutylicum in biofilms of a BES are imaged and compared with conventional biofilms. Under all observed conditions, the cells possess filamentous appendages with a higher number and density in the BES. Differences in the amount of extracellular polymeric substance in the biofilms of the electrodes lead to the conclusion that the cathode can be used as electron donor and the anode as electron acceptor by C. acetobutylicum. When using conductive atomic force microscopy, a current response of about 15 nA is found for the cell appendages from the BES. This is the first report of conductivity for clostridial cell appendices and represents the basis for further studies on their role for biofilm formation and electron transfer.},
  language  = {en}
}
@article{HengsbachEngelCwienczeketal.2023,
  author    = {Hengsbach, Jan-Niklas and Engel, Mareike and Cwienczek, Marcel and Stiefelmaier, Judith and Tippk{\"o}tter, Nils and Ulber, Roland},
  title     = {Scalable unseparated bioelectrochemical reactors by using a carbon fiber brush as stirrer and working electrode},
  series = {ChemElectroChem},
  volume    = {10},
  journal   = {ChemElectroChem},
  number    = {21},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {2196-0216},
  doi       = {10.1002/celc.202300440},
  pages     = {9 Seiten},
  year      = {2023},
  abstract  = {The concept of energy conversion into platform chemicals using bioelectrochemical systems (BES) has gained increasing attention in recent years, as the technology simultaneously provides an opportunity for sustainable chemical production and tackles the challenge of Power-to-X technologies. There are many approaches to realize the industrial scale of BES. One concept is to equip standard bioreactors with static electrodes. However, large installations resulted in a negative influence on various reactor parameters. In this study, we present a new single-chamber BES based on a stirred tank reactor in which the stirrer was replaced by a carbon fiber brush, performing the functions of the working electrode and the stirrer. The reactor is characterized in abiotic studies and electro-fermentations with Clostridium acetobutylicum. Compared to standard reactors an increase in butanol production of 20.14±3.66 \% shows that the new BES can be efficiently used for bioelectrochemical processes.},
  language  = {en}
}