Synthesis of Acetyl-CoA from Carbon Dioxide in Acetogenic Bacteria
Bacterial species, which are able to fix CO2 + H2 as only carbon and energy source to acetyl-CoA and further to acetate, are called acetogens. The pathway acetogenic bacteria possess is the linear, two-branched reductive acetyl-CoA pathway (Wood-Ljungdahl pathway), which they not only use to fix CO2 + H2 and/or CO to acetyl-CoA and further to acetate but also for redox balancing when growing on other carbon substrates. Reduction of CO2 to acetate does not leave acetogens with any additional energy in form of ATP for their anabolism. In order to overcome these energetic constraints, acetogens possess additional membrane complexes which couple the electron transfer from reduced ferredoxin to H+ or NAD+ to a proton or sodium ion gradient across the membrane, which in turn can be used by a proton- or sodium ion-dependent ATP synthase for energy conservation. Since acetogens are able to live autotrophically by using H2 + CO2, they are considered to be valuable tools for the fixation of greenhouse gases. Genetic modifications together with fermentative studies have converted these living artists to strong work horses for production of biofuels and synthetic compounds that help to prevent further global warming and the exploitation of our planet’s fossil fuels.
The work of the authors’ laboratory is supported by grants from the Deutsche Forschungsgemeinschaft and the Federal Ministry of Education and Research.
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