Promoting interspecies electron transfer with biochar

Abstract

Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with Geobacter sulfurreducens or Methanosarcina barkeri in which ethanol was the electron donor. Cells were attached to the biochar, yet not in close contact, suggesting that electrons were likely conducted through the biochar, rather than biological electrical connections. The finding that biochar can stimulate DIET may be an important consideration when amending soils with biochar and can help explain why biochar may enhance methane production from organic wastes under anaerobic conditions.

Figure 1

(A) Ethanol consumption and (B) succinate production with different types of biochar by a syntrophic co-culture of G. metallireducens and G. sulfurreducens. As control experiments we tested all different biochars with no cells, the co-culture without biochar and the co-culture with soluble components released from the biochar. The error bars represent standard deviations of the mean for triplicate cultures.

Figure 2

(A) Protein in 10 mL of medium on day 0 and day 10 in the planktonic phase and attached to BEC biochar, and (B) quantitative PCR analysis of the cells attached to the BEC biochar on day 10 in the G. metallireducens/G. sulfurreducens co-cultures. The error bars represent standard deviations of the mean for triplicate cultures.

Figure 3. Scanning electron micrograph of one of the biochar tested (BEC) with a syntrophic co-culture of G. metallireducens and G. sulfurreducens.

Figure 4

Ethanol consumption, succinate and acetate production in medium with ethanol as the electron donor with (A) G. metallireducens and the BEC biochar or (B) G. metallireducens alone. The error bars represent standard deviations of the mean for triplicate cultures.

Figure 5

Ethanol consumption, methane and acetate production in (A) co-cultures of G. metallireducens-M. barkeri with the BEC biochar, (B) unamended co-cultures of G. metallireducens-M. barkeri (C) and pure culture of M. barkeri with the BEC biochar, and (D) co-cultures of G. metallireducens-M. barkeri with the soluble components released from the BEC biochar. The error bars represent standard deviations of the mean for triplicate cultures.

Figure 6

(A) Protein in 10 mL of medium on day 0 and day 20 in the planktonic phase and attached to BEC biochar, and (B) Quantitative PCR analysis of the cells attached to the BEC biochar on day 20 in the G. metallireducens/M. barkeri co-cultures. The error bars represent standard deviations of the mean for triplicate cultures.

Figure 7. Scanning electron micrograph of a syntrophic co-culture of G. metallireducens (rods) and M. barkeri (spheres) with the BEC biochar.

The white arrow points to the representative cells.