Electricity from methane by reversing methanogenesis

Abstract

Given our vast methane reserves and the difficulty in transporting methane without substantial leaks, the conversion of methane directly into electricity would be beneficial. Microbial fuel cells harness electrical power from a wide variety of substrates through biological means; however, the greenhouse gas methane has not been used with much success previously as a substrate in microbial fuel cells to generate electrical current. Here we construct a synthetic consortium consisting of: (i) an engineered archaeal strain to produce methyl-coenzyme M reductase from unculturable anaerobic methanotrophs for capturing methane and secreting acetate; (ii) micro-organisms from methane-acclimated sludge (including Paracoccus denitrificans) to facilitate electron transfer by providing electron shuttles (confirmed by replacing the sludge with humic acids), and (iii) Geobacter sulfurreducens to produce electrons from acetate, to create a microbial fuel cell that converts methane directly into significant electrical current. Notably, this methane microbial fuel cell operates at high Coulombic efficiency.

Electroactive microorganisms in bioelectrochemical systems

“…Direct evidence for methanol being an intermediate in power generation from methane was shown in a two-stage process where methane was converted to methanol by methanogens in the first stage, and power was produced in a second-stage MFC likely from methanol oxidation to acetate 62 . Another study genetically engineered the methanogen Methanosarcina acetivorans to produce current in an MFC from methane, but other known exoelectrogens identified in the biofilm were thought to be responsible for current generation 63 .…”

“…Synthetic biology can also enable a microorganism to use new substrates or to produce chemicals that can be used for current generation by exoelectrogens. For example, a M. acetivorans strain, engineered to express methyl-coenzyme M reductase (derived from anaerobic methylotrophs), converted methane into acetate, which then fuelled current generation by G. sulfurreducens 63 . In a methane-acclimated sludge that included Paracoccus denitrificans, a microorganism that produces electron shuttles, this synthetic consortium achieved a power density of 168 ± 9 mW m −2 .…”

Viable But Non-Culturable Cells Are Persister Cells

“…For VBNC cultures (5 weeks), 10 mL of cells were treated with ampicillin (100 µg/mL) for 3 h at 37°C to remove exponentially-growing cells, pelleted, washed once with 1 mL of normal saline, and resuspended in 1 mL of normal saline (10-fold 240 concentration). In brief, for double staining 43 , cells were pelleted and fixed with 2% glutaraldehyde in 0.1M sodium cacodylate buffer for 1 to 12 h. Pellets were washed three times for 5 minutes with 0.1 M sodium cacodylate followed by secondary fixation with 1% osmium tetroxide for 1 h in the dark at room temperature. Next, samples were washed three times for 5 min with 0.1 M sodium cacodylate and for 5 minutes with water followed by en bloc staining with 2% uranyl acetate for 1-12 h. Samples were then 245 dehydrated by using a series of ethanol washes (50%, 70%, 85%, and 95%, 3 x 100%), washed three times for 5 min with acetone, and embedded in Epon-Araldite (Ted Pella Inc, Redding, CA, USA).…”

Microbial Interconversion of Alkanes to Electricity

“…To harvest the biochemically produced electrons, the bacteria that naturally consume them ( Figure 1B, green) need to be replaced. The classical way is to replace the bacteria by a fuel-cell cathode in one device (bio fuel cell), in which the compartments are separated by an ion-conductive membrane (Logan et al, 2006;McAnulty et al, 2017;Schröder and Harnisch, 2017). An alternative approach is replacing the bacteria by an auxiliary redox reaction, which is described here in more detail.…”