Today, biomass covers about 10% of the world's primary energy demand. Against a backdrop of rising crude oil prices, depletion of resources, political instability in producing countries and environmental challenges, besides efficiency and intelligent use, only biomass has the potential to replace the supply of an energy hungry civilisation. Plant biomass is an abundant and renewable source of energy-rich carbohydrates which can be efficiently converted by microbes into biofuels, of which, only bioethanol is produced on an industrial scale today. Biomethane is produced on a large scale, but is not yet utilised for transportation. Biobutanol is on the agenda of several companies and may be used in the near future as a supplement for gasoline, diesel and kerosene, as well as contributing to the partially biological production of butyl-t-butylether, BTBE as does bioethanol today with ETBE. Biohydrogen, biomethanol and microbially made biodiesel still require further development. This paper reviews microbially made biofuels which have potential to replace our present day fuels, either alone, by blending, or by chemical conversion. It also summarises the history of biofuels and provides insight into the actual production in various countries, reviewing their policies and adaptivity to the energy challenges of foreseeable future.

Clostridial acetone-butanol fermentation from renewable carbohydrates used to be the largest biotechnological process second only to yeast ethanol fermentation and the largest process ever run under sterile conditions. With the rising prices for mineral oil, it has now the economical and technological potential to replace petrochemistry for the production of fuels from renewable resources. Various methods for using non-food biomass such as cellulose and hemicellulose in agricultural products and wastes have been developed at laboratory scale. To our knowledge, the AB plants in Russia were the only full-scale industrial plants which used hydrolyzates of lignocellosic waste for butanol fermentation. These plants were further developed into the 1980s, and the process was finally run in a continual mode different from plants in Western countries. A biorefinery concept for the use of all by-products has been elaborated and was partially put into practice. The experience gained in the Soviet Union forms a promising basis for the development of modern large-scale processes to replace a considerable fraction of the current chemical production of fuel for our future needs on a sustainable basis.

Clostridium thermocellum produces the most efficient enzyme-complex for the degradation of polysaccharides in biomass, the large extracellular cellulosome. The draft complete genomic sequence of Clostridium thermocellum was screened for open reading frames (ORF) containing cellulosomal dockerin sequences. Seventy-one putative cellulosomal genes were detected. One third of these ORFs may be involved in cellulose hydrolysis. Most of the others showed homology to hemicellulases, pectinases, chitinases, glycosidases or esterases potentially involved in the unwrapping of cellulose fibers. To identify the predominant catalytic components, cellulosomes were purified and the components were separated by an adapted two-dimensional gel electrophoresis technique. The apparent major spots were identified by MALDI-TOF/TOF. Ten of the components were previously known: the structural protein CipA, the endo-glucanases Cel8A, Cel5G, Cel9N, the cellobiohydrolases Cbh9A, Cel9K, Cel48S, the xylanases Xyn10C, Xyn10Z, and the chitinase Chi18A. In addition, three hitherto unknown major components were detected, Cel9R, Xyn10D and Xgh74A. These major components in the cellulosomal particles most probably constitute the essential enzymes for crystalline cellulose hydrolysis.