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. 2019 Feb 20;9(1):2356.
doi: 10.1038/s41598-018-38006-3.

A variety of hydrogenotrophic enrichment cultures catalyse cathodic reactions

Soroush Saheb-Alam  1 , Frank Persson  2 , Britt-Marie Wilén  2 , Malte Hermansson  3 , Oskar Modin  2
Affiliations

A variety of hydrogenotrophic enrichment cultures catalyse cathodic reactions

Soroush Saheb-Alam et al. Sci Rep. .

Abstract

Biocathodes where living microorganisms catalyse reduction of CO2 can potentially be used to produce valuable chemicals. Microorganisms harbouring hydrogenases may play a key role for biocathode performance since H2 generated on the electrode surface can act as an electron donor for CO2 reduction. In this study, the possibility of catalysing cathodic reactions by hydrogenotrophic methanogens, acetogens, sulfate-reducers, denitrifiers, and acetotrophic methanogens was investigated. The cultures were enriched from an activated sludge inoculum and performed the expected metabolic functions. All enrichments formed distinct microbial communities depending on their electron donor and electron acceptor. When the cultures were added to an electrochemical cell, linear sweep voltammograms showed a shift in current generation close to the hydrogen evolution potential (-1 V versus SHE) with higher cathodic current produced at a more positive potential. All enrichment cultures except the denitrifiers were also used to inoculate biocathodes of microbial electrolysis cells operated with H+ and bicarbonate as electron acceptors and this resulted in current densities between 0.1-1 A/m2. The microbial community composition of biocathodes inoculated with different enrichment cultures were as different from each other as they were different from their suspended culture inoculum. It was noteworthy that Methanobacterium sp. appeared on all the biocathodes suggesting that it is a key microorganism catalysing biocathode reactions.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(A) Optical density, (B) H2 consumption rate and CH4 production rate in the methanogenic enrichments (MgenH).
Figure 2
Figure 2
(A) Optical density, (B) volatile fatty acid (VFA) production and H2 consumption rates, (C) acetate and butyrate concentrations in the acetogenic enrichments (Agen).
Figure 3
Figure 3
(A) Optical density, (B) SO4−2 and H2 consumption rates in the sulfate-reducing enrichments (SR). (C) Optical density, (D) NO3− and H2 consumption rates in the denitrifying enrichments (NR).
Figure 4
Figure 4
(A) Optical density, (B) acetate consumption and methane production rates in acetotrophic methanogenic enrichments (MgenA).
Figure 5
Figure 5
Current generation in MECs inoculated by MgenH1, Agen1, MgenA1, and SR1. The cathode potential was lowered from −0.65 V to −0.8 V versus SHE on day 49 in MgenH and Agen and on day 44 in MgenA and SR MECs as indicated by the dashed vertical lines.
Figure 6
Figure 6
Five different CV tests carried out for MgenH-, Agen-, MgenA-, and SR-MECs. The control CV was carried out without the presence of microorganisms.
Figure 7
Figure 7
Relative abundance of the 25 most abundant taxa in the inoculum, suspended enrichments, and on the cathodes after 63 days of operation of the MECs. SV followed by a number means that the sequence could not be classified to a known genus.
Figure 8
Figure 8
Principle coordinate analysis based on a matrix of pairwise dissimilarities between samples calculated the beta component of Hill numbers of order 1.
See this image and copyright information in PMC

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