ABSTRACTClostridium aceticumwas the first isolated autotrophic acetogen, converting CO2plus H2or syngas to acetate. Its genome has now been completely sequenced and consists of a 4.2-Mbp chromosome and a small circular plasmid of 5.7 kbp. Sequence analysis revealed major differences from other autotrophic acetogens.C. aceticumcontains an Rnf complex for energy conservation (via pumping protons or sodium ions). Such systems have also been found inC. ljungdahliiandAcetobacterium woodii. However,C. aceticumalso contains a cytochrome, as doesMoorella thermoacetica, which has been proposed to be involved in the generation of a proton gradient. Thus,C. aceticumseems to represent a link between Rnf- and cytochrome-containing autotrophic acetogens. InC. aceticum, however, the cytochrome is probably not involved in an electron transport chain that leads to proton translocation, as no genes for quinone biosynthesis are present in the genome.IMPORTANCEAutotrophic acetogenic bacteria are receiving more and more industrial focus, as CO2plus H2as well as syngas are interesting new substrates for biotechnological processes. They are both cheap and abundant, and their use, if it results in sustainable products, also leads to reduction of greenhouse gases.Clostridium aceticumcan use both gas mixtures, is phylogenetically not closely related to the commonly used species, and may thus become an even more attractive workhorse. In addition, its energy metabolism, which is characterized here, and the ability to synthesize cytochromes might offer new targets for improving the ATP yield by metabolic engineering and thus allow use ofC. aceticumfor production of compounds by pathways that currently present challenges for energy-limited acetogens.
Metabolic engineering of Moorella thermoacetica for thermophilic bioconversion of gaseous substrates to a volatile chemical
