Abstract
BackgroundMagnetite-mediated direct interspecies electron transfer (DIET) between Geobacter and Methanosarcina species is increasingly being invoked to explain magnetite stimulation of methane production in anaerobic soils and sediments. Although magnetite-mediated DIET has been documented in defined co-cultures reducing fumarate or nitrate as the electron acceptor, the effects of magnetite have only been inferred in methanogenic systems.MethodsConcentrations of methane and organic acid were analysed with a gas chromatograph and high-performance liquid chromatography, respectively. The concentration of HCl-extractable Fe(II) was determined by the ferrozine method. The association of the defined co-cultures of G. metallireducens and M. barkeri with magnetite was observed with transmission electron micrographs.ResultsMagnetite stimulated ethanol metabolism and methane production in defined co-cultures of G. metallireducens and M. barkeri; however, magnetite did not promote methane production in co-cultures initiated with a culture of G. metallireducens that could not produce electrically conductive pili (e-pili), unlike the conductive carbon materials that facilitate DIET in the absence of e-pili. Transmission electron microscopy revealed that G. metallireducens and M. barkeri were closely associated when magnetite was present, as previously observed in G. metallireducens/G. sulfurreducens co-cultures. These results show that magnetite can promote DIET between Geobacter and Methanosarcina species, but not as a substitute for e-pili, and probably functions to facilitate electron transfer from the e-pili to Methanosarcina.ConclusionIn summary, the e-pili are necessary for the stimulation of not only G. metallireducens/G. sulfurreducens, but also methanogenic G. metallireducens/M. barkeri co-cultures with magnetite.
Highlights
Microbial methane production is one of the most successful, large-scale bioenergy strategies (Liu et al, 2009; Shen et al, 2016) and methane production in terrestrial environments isHow to cite this article Wang et al (2018), Necessity of electrically conductive pili for methanogenesis with magnetite stimulation
Not, magnetite was capable of stimulating direct interspecies electron transfer (DIET) between G. metallireducens and M. barkeri, co-cultures were initiated with ethanol as the sole electron donor in the presence, and absence, of magnetite
M. bakeri is capable of using H2 as an electron donor, G. metallireducens cannot metabolise ethanol with the production of H2 (Rotaru et al, 2014b; Shrestha et al, 2013a; Summers et al, 2010) and syntrophic growth in G. metallireducens/M. barkeri co-cultures can be attributed to DIET
Summary
Microbial methane production is one of the most successful, large-scale bioenergy strategies (Liu et al, 2009; Shen et al, 2016) and methane production in terrestrial environments isHow to cite this article Wang et al (2018), Necessity of electrically conductive pili for methanogenesis with magnetite stimulation. Magnetite stimulated ethanol metabolism and methane production in defined co-cultures of G. metallireducens and M. barkeri; magnetite did not promote methane production in co-cultures initiated with a culture of G. metallireducens that could not produce electrically conductive pili (e-pili), unlike the conductive carbon materials that facilitate DIET in the absence of e-pili. Transmission electron microscopy revealed that G. metallireducens and M. barkeri were closely associated when magnetite was present, as previously observed in G. metallireducens/G. sulfurreducens co-cultures. These results show that magnetite can promote DIET between Geobacter and Methanosarcina species, but not as a substitute for e-pili, and probably functions to facilitate electron transfer from the e-pili to Methanosarcina. The e-pili are necessary for the stimulation of G. metallireducens/G. sulfurreducens, and methanogenic G. metallireducens/M. barkeri cocultures with magnetite
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