In anoxic environments, cellulose, a polymer of glucose, is fermented to CO2 and methane via a syntrophic association of anaerobic bacteria, protozoa and fungi that ferment cellulose to acetic acid, CO2, and H2 and of methanogenic archaea that convert acetic acid, CO2, and H2 to methane. There is no organism known that can ferment glucose to 3 CO2 and 3 CH4 alone. A kinetic theory relating growth rates to the length of metabolic pathways and the number of coupling sites can explain these finding for energy substrate-limited planktonic cells (Pfeiffer, T., Schuster, S. & Bonhoeffer, S. (2001) Cooperation and Competition in the Evolution of ATP-Producing Pathways. Science 292, 504-507). The same theory predicts, however, that methanogens capable of fermenting glucose to CO2 and methane should exist in biofilms. To test this, we cloned the genes required for glucose-import (glucose transport facilitator from Zymomonas mobilis) and glucose activation to glucose-6-phosphate (glucokinase from E. coli) into Methanosarcina acetivorans, a methanogen lacking only these genes for methanogenesis from glucose. And indeed we found that cell suspensions of recombinant M. acetivorans are capable of methanogenesis from glucose, albeit presently at only very low specific rates (see Fig.). Next, the rate limiting steps in this fermentation will have to be identified and to be overcome.
From 2013 on Michael Rother will continue the project alone at the University of Dresden, where he in the meantime moved to. In the last two years the project was financed by the LOEWE center SYNMIKRO in Marburg.
Participants: R. Thauer with Christian Sattler in cooperation with Prof.Dr. Michael Rother, University Frankfurt; from 10/2011 at Technischen Universität Dresden