NOVELTY - System comprises: (a) one or more microorganisms that hydrolyzes and ferments hexose and pentose carbohydrates, where the one or more microorganisms forms a biofilm; (b) a biomass comprising hexose and pentose carbohydrates; and (c) a bioreactor comprising an impeller.    USE - The system and methods are useful for culturing microorganism; and for producing fermentation end product (all claimed).    ADVANTAGE - The invention provides compositions and methods for improving the efficiency of biofuels and chemicals, e.g. ethanol, production.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are: (1) a system comprising: (a) a biomass comprising hexose and pentose carbohydrates; (b) one or more microorganisms comprising Clostridium phytofermentans, Clostridium sp. Q.D., or its variant, where the one or more microorganisms forms a biofilm on the biomass or a support; and (c) a bioreactor comprising a helical impeller that has a revolution rate of about 100-200 revolutions per minute (rpm); (2) a method of culturing a microorganism comprising: (a) contacting a biomass comprising hexose and pentose carbohydrates with one or more microorganisms that hydrolyzes and ferments hexose and pentose carbohydrates., or its variant; and (b) culturing the one or more microorganisms by agitating the biomass and the one or more microorganisms at a rate where the one or more microorganisms forms a biofilm on the surface of the biomass or a support; or a method of culturing a microorganism comprising: (a) contacting biomass comprising hexose and pentose carbohydrates with one or more microorganisms comprising Clostridium phytofermentans, Clostridium sp. Q.D., or its variant, where the one or more microorganisms forms a biofilm on the biomass or a support; and (b) culturing the one or more microorganisms in a bioreactor by agitating the biomass with an impeller at a rate that the biofilm remains substantially intact; (3) a method of producing fermentation end product comprising: (a) contacting biomass with a medium and one or more microorganisms that hydrolyzes and ferments hexose and pentose carbohydrates that forms a biofilm on the biomass or a support; (b) culturing the one or more microorganisms in the bioreactor with a low sheer force so that the biofilm remains substantially intact; (c) producing a fermentation end product from the biomass by the one or more microorganisms; and (d) separating the fermentation end product from the one or more microorganisms and the biomass; (4) a fermentation end product produced by the method; and (5) a composition for the production of a fermentative end product comprising: (a) a biomass comprising hexose and pentose carbohydrates; and (b) one or more microorganisms that hydrolyzes and ferments hexose and pentose carbohydrates, where the one or more microorganisms forms a biofilm.