Paper BI+AS-TuM13
Direct Interspecies Electron Transfer (DIET) in Syntrophic Microbes

Tuesday, October 22, 2019, 12:00 pm, Room A120-121

Presentation Summary:

This presentation will show our recent results of metabolic performance of direct interspecies electron transfer between syntrophic Geobacter species by using in situ liquid time-of-flight secondary ion mass spectrometry (ToF-SIMS).

Abstract

Direct interspecies electron transfer (DIET) is deemed important and effective for electron exchange among syntrophic Geobacter species. DIET facilitates coupling of carbon, nitrogen, phosphorus biogeochemical cycles in the natural anaerobic environment [1]. In this presentation, Geobacter sulfurreducens and Geobacter metallireducens were employed to investigate the metabolic behavior of a syntrophic community cultured in a SALVI microfluidic reactor and analyzed by in situ liquid time-of-flight secondary ion mass spectrometry (ToF-SIMS). More types of molecules that facilitate metallic-like electron conductivity pilis or cellular outer-membrane cytochrome (e.g., OmcS) formation in the Geobacter co-culture community were observed than the planktonic cells. Characteristic peaks observed include aromatic acids m/z⁺ 82 (C₄H₆N₂⁺, histidine), 120 (C₈H₁₀N⁺, phenylalanine), and 166 (C₉H₁₂NO₂⁺, phenylalanine), benzene polymers m/z^- 93 (C₆H₅O^-), 94 (C₆H₆O^-), and 133 (C₉H₉O^-) in the co-cultured aggregate. The compositions of specific fatty acid also changed according to the culture condition when comparing the single population vs. co-cultured community. Abundance of water clusters were observed in this work and the water cluster differences observed among the cultured community, single population biofilms, or planktonic cells also suggest that other living activities of cells is possible, for instance, moderation of the solvation spheres when forming the aggregates due to IET and/or DIET. Alternatively, we hypothesize that proton-coupled electron transfer (PCET) may play a role in the syntrophic community besides DIET based on in vivo spectral comparisons. Our in situ molecular imaging results lead to the following conclusions: 1) interspecies electron transfer in co-cultured planktonic states may be mainly mediated by reduced molecular hydrogen; and 2) DIET in co-cultured aggregates functions via direct contact or microbial nanowire. Our findings improve the understanding of the electron transfer in syntrophic communities based on in vivo molecular imaging.

Key words: direct interspecies electron transfer (DIET), interspecies electron transfer, Geobacter sulfurreducens, Geobacter metallireducens, in situ liquid TOF-SIMS

References:

1. D.R. Lovley, et al., Geobacter: the microbe electric's physiology, ecology, and practical applications. Adv. Microbiol. Physiol., 59, 1-100, 2011.