Clostridium ljungdahlii was metabolically engineered for the production of bulk chemical and next generation biofuel 1-butanol from synthesis gas by transformation with a plasmid harbouring the butanol synthesis genes from Clostridium acetobutylicum. Synthesis gas (a mixture of CO, CO2 and H2) can be easily produced by gasification of biomass or municipal waste. Thus, this process presents an alternative to conventional butanol fermentation (which uses corn or sugar as substrate and therefore competes with the food industry) and also chemical butanol production (which starts from propen obtained from non-renewable sources). To optimize the process, metagenomic libraries from environmental sources were screened for novel butanol dehydrogenases. Four respective enzymes could be identified and characterized in detail. Further studies on the metabolism of C. ljungdahlii revealed a new type of energy conservation in acetogenic bacteria. There are indications that Clostridium difficile might also belong to this group, as respective genes were found in the genome sequence and weak autotrophic growth occurred on a mixture of CO2 and H2.