Why Sequence a Benzene-Degrading Methanogenic Consortium?

As recently as the 1990’s, aromatic hydrocarbons like benzene and toluene were thought to be resistant to degradation under anaerobic conditions. It is now appreciated that biodegradation in the absence of oxygen contributes significantly to the attenuation of hydrocarbons and other pollutants in the environment. Unravelling the yet unknown pathways and mechanisms of anaerobic benzene metabolism is a critical milestone for hydrocarbon bioremediation. While many pathways have been suggested, none has been proven, and no genes or enzymes are known. The elucidation of this pathway, including the identification of the genes and enzymes involved, is vital for the demonstration, validation, and regulatory acceptance of in-situ bioremediation as a cost-effective cleanup strategy for cleanup of benzene-contaminated aquifers.

The benzene-degrading consortium to be sequenced offers a practical advantage over Dechloromonas aromatica strain RCB, the only organism in pure culture that can oxidize benzene in the absence of oxygen, in that it detoxifies benzene without the need to provide an exogenous electron acceptor. In this culture, fermenting and acetogenic bacteria rely on methanogenic archaea to maintain low concentrations of hydrogen and acetate to drive otherwise thermodynamically unfavorable reactions. As a result of these syntrophic interactions, it has proven difficult to isolate the benzene-degrading organisms, rendering many traditional pure-culture methods for elucidating metabolic pathways infeasible. Community genome sequencing offers an exciting and promising approach to unravel metabolic pathways and regulation in this community without needing to isolate individuals. This approach will also enable investigations of gene expression and signaling between members of the community that are not possible with pure cultures.

Principal Investigators: Elizabeth A. Edwards and Radhakrishnan Mahadevan (Univ. of Toronto)