NOVELTY - Organism capable of fermenting a saccharification product of a substrate derived from a biomass, where a first gene endogenous to the organism has been inactivated by genetic engineering, the first gene encoding a post-translational modifying protein, and the inactivation of the first gene results in a decrease in hydrogenase activities in the organism, is new.    USE - The organism is useful for: fermenting a saccharification product of a substrate derived from a biomass; and producing ethanol (claimed).    ADVANTAGE - The organism is capable of producing ethanol in an economical manner with high yield.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for: (1) a method for producing ethanol, comprising either creating the organism with at least one gene inactivated, the gene encoding a post-translational modifying protein, where the posttranslational modifying protein is capable of facilitating maturation of at least one hydrogenase synthesized by the organism in its native state, and incubating the organism in a medium containing at least one substrate comprises glucose, xylose, mannose, arabinose, galactose, fructose, cellobiose, sucrose, maltose, xylan, mannan, starch, cellulose, and/or pectin to production of ethanol from the substrate, or providing within a reaction vessel, a reaction mixture comprising a carbohydrate rich biomass substrate, and a fermentation agent, the fermentation agent comprising a bacterium that has been genetically modified to inactivate a first gene endogenous to the bacterium, the first gene encoding a posttranslational modifying protein, where the reaction mixture is incubated under suitable conditions for a period of time sufficient to allow saccharification and fermentation of the carbohydrate-rich biomass substrate; (2) a bacterium capable of fermenting a saccharification product of a carbohydrate-rich biomass substrate, where the hydG and lactate dehydrogenase (ldh gene) genes are inactivated by genetic engineering; and (3) a Clostridium thermocellum strain deposited under patent deposit designation No. PTA-11763 or PTA-11764.