BayCEER Workshop 2020

Long-distance electron transfer in mining-impacted freshwater lake sediments of the Fichtelgebirge

P 3.14 in Research Poster Kaleidoscope

Water-saturated soils and sediments are characterized by steep redox gradients, in which thermodynamically attractive electron donors and acceptors are often not simultaneously available. Cable bacteria of the family Desulfobulbaceae can overcome this by spatially coupling redox half reactions over cm-distances. Cable bacteria are known to conduct electrogenic sulphide oxidation (e-Sox), in which sulphide oxidation at the anodic side of the filament is coupled to oxygen respiration at the cathodic end. Here, we want to show that long-distance electron transfer by filamentous bacteria also plays a role in -partially acidic- sediments of historically mining-impacted lakes of the Fichtelgebirge. Samples from lakes Fichtelsee and Weißenstädter See and rivers Eger and Lehstenbach were incubated as static flooded laboratory columns, including a vertical agar pillar embedded within the soil cores as “diffusion highway” and possible means for cable bacteria enrichment. Porewater concentrations of oxygen and sulphide and pH changes over depth were monitored using microsensors. Changes in community composition were examined by Illumina sequencing and fluorescence in situ hybridization. Our results show that the sulfidic zone gradually shifted deeper into the core, accompanied by appearance of a pH peak at the oxic-anoxic gradient, indicating long-distance electron transfer. Microscopy of this zone showed the formation of long filaments. With next generation sequencing Desulfobulbaceae were discovered in sediment and enriched in the agar pillar. There, Desulfobulbaceae co-occurred frequently with fermenters. To our knowledge, we are the first to report long-distance electron transfer by filamentous bacteria for mining-impacted acidic sediments.

Keywords: freshwater cable bacteria, 16S amplicon sequencing, microprofiling, electrogenic sulfur oxidation (e-SOX), Desulfobulbaceae