Filamentous bacteria transport electrons over centimetre distances

Abstract

Oxygen consumption in marine sediments is often coupled to the oxidation of sulphide generated by degradation of organic matter in deeper, oxygen-free layers. Geochemical observations have shown that this coupling can be mediated by electric currents carried by unidentified electron transporters across centimetre-wide zones. Here we present evidence that the native conductors are long, filamentous bacteria. They abounded in sediment zones with electric currents and along their length they contained strings with distinct properties in accordance with a function as electron transporters. Living, electrical cables add a new dimension to the understanding of interactions in nature and may find use in technology development.

Centimeter-long electron transport in marine sediments via conductive minerals

“…This compares well with the currents of 14-86 mA estimated from oxygen consumption in the sediments (Nielsen et al, 2010) in which it was proposed that microbial filaments were responsible for long-range electron transport (Pfeffer et al, 2012).…”

“…Although it has been suggested that filaments of cells closely related to Desulfobulbus species accounted for conductivity to reduced marine sediments from Aarhus Bay, it is, in fact, unknown whether this is possible because the conductivity of the filaments was not demonstrated (Pfeffer et al, 2012;Reguera, 2012;Malkin et al, 2014). No long bacterial filaments were observed in the Nantucket sediments used in these studies.…”

“…The suppression of sediment conductivity with oxidation indicated that long-range electron transport through the sediments is significantly different than that through G. sulfurreducens biofilms. It is unknown how oxidizing conditions might have an impact on the previously proposed conductivity through filamentous bacteria (Pfeffer et al, 2012;Malkin et al, 2014) because the hypothesized conductivity and the mechanisms for conduction have not been documented (Reguera, 2012). …”

“…In previous studies (Nielsen et al, 2010) that led to the concept of long-range electron transport via conductive microbial filaments (Pfeffer et al, 2012), electric currents in the sediment were not actually measured, but rather inferred from rates of sediment oxygen consumption that were estimated from oxygen concentration profiles (Nielsen et al, 2010). In Aarhus Bay, estimated rates of oxygen consumption were 9.7 mmol O 2 per m 2 per day with 31% of this oxygen consumption attributed to electric current from deeper sediments (that is, 3 mmol O 2 per m 2 per day) and in Aarhus Harbor sediments 42% of the estimated 46 mmol O 2 per m 2 consumed per day (that is, 19.3 mmol O 2 per m 2 per day) was attributed to the inferred electric currents (Nielsen et al, 2010).…”

Use of Novel Reinforced Cation Exchange Membranes for Microbial Fuel Cells

“…Geobacter metallireducen familiar for their electrochemical activity in MFCs have been found enriched in the 'hybrid-H', recent report also coherence with activity in high salt concentrations [53]. Indeed, in extreme haloalkalophile Desulfurivibrio alkaliphilus, which is a sulfate reducing bacteria commonly found in soda lakes [54], Interestingly, Desulfurivibrio alkaliphilus is also found in long rang electron transfer through filaments, in which its activity might be employed to form an electrochemical activity in MFC [55]. Recently, Marinobacter adhaerens is known for their electrochemical activity on copper alloy [56].…”