Research on the metabolism of extremophilic bacteria (Thermotoga, Caldicellulosiruptor) and archaea (Pyrococcus, Thermococcus) has been ongoing for many years, and focused on their sugar catabolism, central metabolic pathways, hydrogen production and archaeal lipid biosynthesis. Currently, extremophile research is more directed towards the fundamental aspects of chromosome segregation, involving state-of-the art protein imaging techniques. In addition to the extremophile work, research also encompasses mesophilic solventogenic and acetogenic Clostridia. These microorganisms have various metabolic features, like butanol formation and fixation of C1-gases (CO/CO2), that make them interesting for biotechnological purposes. By making use of novel genome editing tools, we want to engineer the metabolism of these fermentative anaerobes, and apply them for the bio-based production of fuels and chemicals.