Microbial communities represent a powerful tool for catalysis of a multitude of processes beneficial to humankind and the environment. In many respects microbial technologies such as bioremediation, biogas production and biomining simply involve microbes manipulating the redox state of chemicals.
The behaviour of a microbial community can in part be described as a cascade of electron transfer reactions, analogous to a circuit board, with the outcome being oxidation of electron donors and the reduction of electron acceptors. The challenge in manipulating microbial communities that serve to oxidize or reduce specific chemicals is therefore to channel electron transfer in the biological circuit to a desired end point.
In our work on the biological degradation of chlorinated solvents we have exploited groups of bacteria encoding reductive dehalogenase enzymes. The primary approach, whether in situ or ex situ, is to direct electron flow towards chlorinated solvents by increasing the abundance of the so called organochlorine respiring bacteria within the community.
A distinct approach, with which we have also had success, is the application of small redox active molecules (electron shuttles) that can be reduced by a broad variety of bacteria and subsequently catalyse the abiotic reduction of chlorinated solvents. This latter approach has now also been exploited in our work on biogas production from renewable and non-renewable energy resources. Experiments have been performed in which the production of methane from coal can be increased by an order of magnitude through application of a phenazine type electron shuttle. Similar results have been obtained with food waste or marine algae as an organic feedstock. The impact of manipulating electron flow on the microbial community and the mechanism by which methane production is catalysed will be presented.