Pulse electromagnetic fields enhance extracellular electron transfer in magnetic bioelectrochemical systems

Abstract

BackgroundMicrobial extracellular electron transfer (EET) is essential in driving the microbial interspecies interaction and redox reactions in bioelectrochemical systems (BESs). Magnetite (Fe3O4) and magnetic fields (MFs) were recently reported to promote microbial EET, but the mechanisms of MFs stimulation of EET and current generation in BESs are not known. This study investigates the behavior of current generation and EET in a state-of-the-art pulse electromagnetic field (PEMF)-assisted magnetic BES (PEMF-MBES), which was equipped with magnetic carbon particle (Fe3O4@N-mC)-coated electrodes. Illumina Miseq sequencing of 16S rRNA gene amplicons was also conducted to reveal the changes of microbial communities and interactions on the anode in response to magnetic field.ResultsPEMF had significant influences on current generation. When reactors were operated in microbial fuel cell (MFC) mode with pulse electromagnetic field (PEMF-MMFCs), power densities increased by 25.3–36.0% compared with no PEMF control MFCs (PEMF-OFF-MMFCs). More interestingly, when PEMF was removed, the power density dropped by 25.7%, while when PEMF was reintroduced, the value was restored to the previous level. Illumina sequencing of 16S rRNA gene amplicon and principal component analysis (PCA) based on operational taxonomic units (OTUs) indicate that PEMFs led to the shifts in microbial community and changes in species evenness that decreased biofilm microbial diversity. Geobacter spp. were found dominant in all anode biofilms, but the relative abundance in PEMF-MMFCs (86.1–90.0%) was higher than in PEMF-OFF-MMFCs (82.5–82.7%), indicating that the magnetic field enriched Geobacter on the anode. The current generation of Geobacter-inoculated microbial electrolysis cells (MECs) presented the same change regularity, the accordingly increase or decrease corresponding with switch of PEMF, which confirmed the reversible stimulation of PEMFs on microbial electron transfer.ConclusionThe pulse electromagnetic field (PEMF) showed significant influence on state-of-the-art pulse magnetic bioelectrochemical systems (PEMF-MBES) in terms of current generation and microbial ecology. EET was instantaneously and reversibly enhanced in MBESs inoculated with either mixed-culture or Geobacter. PEMF notably decreased bacterial and archaeal diversities of the anode biofilms in MMFCs via changing species evenness rather than species richness, and facilitated specific enrichment of exoelectrogenic bacteria (Geobacter) on the anode surface. This study demonstrates a new magnetic approach for understanding and facilitating microbial electrochemical activities. Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0929-3) contains supplementary material, which is available to authorized users.

Magnet anode enhances extracellular electron transfer and enrichment of exoelectrogenic bacteria in bioelectrochemical systems

“…The power densities generated by the magnetic MFCs were significantly greater than the non-magnetic MFC, with the power density of MFC-80 mT measured around two times higher than that of MFC-0 mT. These results demonstrated that the SMF promoted the power generation of the MFCs, which was also reported in the earlier articles detailing the effect of static magnetic fields or pulse magnetic fields on MFCs [19, 27]. Importantly, the intensity of the SMF needs to be controlled within an appropriate range to obtain the best promotion effect.…”

“…The culture medium of the reactors contained: 2 g/L of sodium acetate, 50 mM of phosphate buffer solution (PBS), 10 mL/L of mineral solution, and 10 mL/L of vitamin solution [27]. The inoculum of the reactors consisted of the activated sludge taken from the secondary clarifier of a local wastewater treatment plant (Harbin, China).…”

“…Magnetic field also facilitates the cytochrome c-mediated bioelectrochemical transformations rates and enhances performance of biofuel cells with different enzyme assemblies attached on electrodes [25, 26]. In our previous study, we found that pulse electromagnetic fields can enhance extracellular electron transfer (EET) and facilitated exoelectrogens ( Geobacter ) enrichment on the anode surface of MFCs resulting in high power generation [27]. The growth of microorganisms can be stimulated or inhibited depending on the intensity of a MF [28], and the appropriate range of a MF intensity that would serve to enrich exoelectrogens, thus enhancing the power generation of MFCs, has not yet been elucidated.…”

Neglected Effects of Inoculum Preservation on the Start-Up of Psychrophilic Bioelectrochemical Systems and Shaping Bacterial Communities at Low Temperature

“…The real condition of the taxonomic level of species for Geobacter might be different depending on whether or not the bacterial proportions were the same in each sample. As far as we know, there are a number of different Geobacter species (Zhou et al, 2017), and the ability of EET is different. Single-molecule sequencing technology with long reads will provide a powerful tool in distinguishing Geobacter spp.…”

The effects of electric, magnetic and electromagnetic fields on microorganisms in the perspective of bioremediation

“…In Zhou et al (2017), a pulsed electromagnetic field (square wave with frequency 100 Hz and intensity 5 lT) applied to a bioelectrochemical system caused changes in the microbial community at the anode: a relatively greater abundance of Geobacter spp. was found (4-8%) than in the control.…”