Long-Term Behavior of Defined Mixed Cultures of Geobacter sulfurreducens and Shewanella oneidensis in Bioelectrochemical Systems

Abstract

This work aims to investigate the long-term behavior of interactions of electrochemically active bacteria in bioelectrochemical systems. The electrochemical performance and biofilm characteristics of pure cultures of Geobacter sulfurreducens and Shewanella oneidensis are being compared to a defined mixed culture of both organisms. While S. oneidensis pure cultures did not form cohesive and stable biofilms on graphite anodes and only yielded 0.034 ± 0.011 mA/cm 2 as maximum current density by feeding of each 5 mM lactate and acetate, G. sulfurreducens pure cultures formed 69 μm thick, area-wide biofilms with 10 mM acetate as initial substrate concentration and yielded a current of 0.39 ± 0.09 mA/cm 2 . Compared to the latter, a defined mixed culture of both species was able to yield 38% higher maximum current densities of 0.54 ± 0.07 mA/cm 2 with each 5 mM lactate and acetate. This increase in current density was associated with a likewise increased thickness of the anodic biofilm to approximately 93 μm. It was further investigated whether a sessile incorporation of S. oneidensis into the mixed culture biofilm, which has been reported previously for short-term experiments, is long-term stable. The results demonstrate that S. oneidensis was not stably incorporated into the biofilm; rather, the planktonic presence of S. oneidensis has a positive effect on the biofilm growth of G. sulfurreducens and thus on current production.

Strategies for the Targeted Improvement of Anodic Electron Transfer in Microbial Fuel Cells

“…A biological approach comprises the genetic modification of electrochemically active microorganisms. The use of defined mixed cultures represents another option, because the electron transfer efficiency can be improved by mutual interactions between organisms , . In physico‐chemical approaches, the electrode surface and its interaction with the microorganisms as well as the application of redox mediators constitute a central aspect of this research .…”

“…Additionally, the current density could be increased to a total of 6000–6400 mA m −2 by cocultivating G. sulfurreducens (generating a current density in the corresponding pure culture of 4700 mA m −2 ), Geobacter metallireducens (600 mA m −2 ) and S. oneidensis (1300 mA m −2 ), which has been associated with both the upregulation of the central metabolism and cytochrome‐related gene expression as well as the interorganismal use of secreted redox mediators . Further investigations confirmed the positive effect of defined mixed cultures of G. sulfurreducens and S. oneidensis on one another based on the 38 % higher current density (5400 ± 700 mA m −2 ) and 35 % thicker biofilm dominated by G. sulfurreducens (93 ± 8 µm) in comparison to the individual pure cultures ( G. sulfurreducens with 3900 ± 900 mA m −2 and S. oneidensis with 340 ± 11 mA m −2 ) .…”

Rational Selection of Carbon Fiber Properties for High-Performance Textile Electrodes in Bioelectrochemical Systems

“…Intruding oxygen can be responsible for an increased biomass on the electrode as well as planktonic growth and flavin production (TerAvest et al, 2014). However, the CE for the respective SB high reactor was 44%, which is higher than results from other studies that claim close to anaerobic conditions (Rosenbaum et al, 2011;Engel et al, 2019), and it was also very close to the average CE of the plate reactor setup. We consequently consider the extraordinary biofilm on SB high to be truly related to the electrode properties.…”

“…All tubings were of low gas permeability and appropriate wall thickness (connection tubes: Norprene R A-60-G and pump tubes: Tygon R F-40-40-A, both ProLiquid GmbH, Germany; inner diameter 1.6/0.51 mm; wall thickness 1.6/0.9 mm; permeability for O 2 is 200/22 cm 3 /([cm Hg]•10 −10 ) at 25 • C, respectively]. CEs ranged around 43 ± 23% (n = 19), which are high for S. oneidensis based BES (literature values range from 10 to 40%; Watson and Logan, 2009;Rosenbaum et al, 2011;Kipf et al, 2013;Engel et al, 2019). Fabric BES were run in biological triplicates or duplicates.…”

Quantification of microaerobic growth ofGeobacter sulfurreducens

“…G. sulfurreducens was cultivated in a minimal medium containing 10 mM acetate as carbon source and electron donor and 40 mM fumarate as electron acceptor as described previously (27–29). For precultures medium was prepared in serum bottles (125 mL with 50 mL liquid volume, Fisher Scientific, Hampton, New Hampshire, USA) and gassed with N 2 for a minimum of 20 min to obtain anaerobic conditions.…”