Biofuel bacteria. Petri dish containing colonies of recombinant (genetically modified) Streptomyces bacteria (red) that may produce cellulase. This is the enzyme that breaks down cellulose (the primary structural material in plants). Bacteria that can produce cellulase, or similar enzymes, are able to ferment plant cellulose to produce ethanol for use as a fuel. Ethanol is added to petrol to improve vehicle performance and reduce air pollution. Fuels produced by biological means (biofuels) are renewable, unlike fossil fuels. The technology has been developed by the National Renewable Energy Laboratory, Golden, Colorado, USA.