TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Microorganism: The metabolic pathway gene is a lactic acid synthesis pathway gene, where the lactic acid synthesis pathway gene is a lactate dehydrogenase (LDH) gene, and where the LDH gene is Cphy1232 or Cphy1117. The microorganism does not express pyruvate decarboxylase. The microorganism does not comprise an integration element in a LDH gene. The microorganism is a mesophilic microorganism. The microorganism is gram negative or gram positive. The microorganism is a Clostridium species, where the Clostridium species is C. phytofermentans or its variant, and where the Clostridium species is Clostridium species Q.D or its variant. The microorganism comprises a heterologous fragment of a LDH gene, where the dehydrogenase gene is Cphy1232 or Cphy1117. The microorganism comprises a heterologous fragment of a phosphotransacetylase (PTA) gene, an acetyl kinase gene, or a pyruvate formate lyase gene, where the gene is Cphy1326, Cphy1327, or Cphy1174. The fragment does not comprise a restriction enzyme site which is cleavable by restriction endonucleases specific to Escherichia coli bacteria. The fragment is methylated prior to integration into the genome of the microorganism. An isolated microorganism is selected from NRRL Accession No. NRRL B-50351, NRRL B-50352, NRRL B-50353, NRRL B-50354, NRRL B-50355, NRRL B-50356, NRRL B-50357, NRRL B-50358, and NRRL B-50359. An isolated mesophilic microorganism lacks LDH activity, where the mesophilic microorganism hydrolyzes and ferments polysaccharides. An isolated mesophilic microorganism, genetically modified to produce higher amounts of ethanol than a non-modified microorganism, where the microorganism is modified to inactivate expression of a gene involved in lactic acid synthesis as compared in the wild-type mesophilic microorganism. An isolated genetically modified Clostridium species is modified to inactivate expression of a lactic acid synthesis gene. A genetically modified C. phytofermentans strain is modified to inactivate expression of a metabolic pathway gene. The microorganism is an anaerobic microorganism that can saccharify both C5 and C6 polysaccharides. A genetically modified C. phytofermentans strain is modified to inactivate expression of a LDH gene. A genetically modified C. phytofermentans strain is modified to inactivate expression of Cphy1232 or Cphy1117. An isolated microorganism ferments cellulosic or lignocellulosic materials to produce ethanol in a concentration that is at least 90% of a theoretical yield, where the microorganism is genetically modified to inactivate a metabolic pathway gene of the wild-type organism. An isolated Clostridium ferments cellulosic or lignocellulosic materials to produce ethanol in a concentration that is at least 90% of a theoretical yield, where the microorganism is genetically modified to inactivate a LDH gene of the wild-type organism. Preferred Product: The biomass comprises cellulosic or lignocellulosic materials. The biomass comprises one or more of corn steep solids, corn steep liquor, malt syrup, xylan, cellulose, hemicellulose, fructose, glucose, mannose, rhamnose, or xylose. The biomass comprises corn steep solids, corn steep liquor, malt syrup, corn stover, bagasse, algae, fruit peels, oat hulls, modified crop plants, poplar, wood, switch grass, distiller's grains, switchgrass, paper, and paper pulp sludge, municipal waste, plant material, plant material extract, a natural or synthetic polymer, or their combination. The biomass is pre-conditioned with acid treatment, alkali treatment or steam explosion. The fermentation end-product is an alcohol, a gas, an acid, a fatty acid, an isoprenoid, or a polyisoprene. The chemical product is ethanol, butanol, methanol, methane, hydrogen, formic acid, or acetic acid. The microorganism is capable of hydrolyzing xylose and/or cellulose. A product for production of a fermentation end-product product, comprises a fermentation vessel comprising a carbonaceous biomass; and a microorganism genetically modified to inactivate expression of a lactic acid synthesis pathway gene of the wild-type organism, where the microorganism hydrolyzes and ferments both C5 and C6 polysaccharides and produces the fermentation end-product. A product for production of a fermentation end-product product, comprises fermentation vessel comprising a carbonaceous biomass; and a C. phytofermentans genetically modified to inactivate expression of Cphy1232 or Cphy1117 gene of the wild-type organism, where the C. phytofermentans hydrolyzes and ferments both C5 and C6 polysaccharides and produces the fermentation end-product. Preferred Method: Producing a fermentation end-product comprises contacting a carbonaceous biomass with a microorganism genetically modified to inactivate expression of a metabolic pathway gene of the wild-type organism, where the microorganism hydrolyzes and ferments both C5 and C6 polysaccharides; and allowing sufficient time for the hydrolysis and fermentation to produce the fermentation end-product. The microorganism modified to enhance production of a fermentive end-product is selected from C. phytofermentans, Clostridium sp. Q.D, Thermoanaerobacter ethanolicus, Clostridium thermocellum, Clostridium beijerinckii, Clostridium acetobutylicum, Clostridium cellovorans, Clostridium tyrobutyricum, Clostridium thermobutyricum, Thermoanaerobacterium saccharolyticum, Thermoanaerobacter thermohydrosulfuricus, Saccharomyces cerevisiae, Clostridium acetobutylicum, Moorella ssp., Carboxydocella ssp., Zymomonas mobilis, E. coli, and Klebsiella oxytoca, or its variant. The biomass is pre-conditioned with acid treatment, alkali treatment or steam explosion. The process occurs at 10-35 degrees C. Producing a fermentation end-product comprises contacting a carbonaceous biomass with a Clostridium species is genetically modified to inactivate expression of a lactic acid pathway gene of the wild-type organism, where the Clostridium species hydrolyzes and ferments both C5 and C6 polysaccharides; and allowing sufficient time for the hydrolysis and fermentation to produce the fermentation end-product. The fragment is methylated prior to integration into the genome of the microorganism. Producing a fermentation end-product comprises contacting a carbonaceous biomass with a C. phytofermentans genetically modified to inactivate expression of a Cphy1232 or Cphy1117 gene of the wild-type organism; and allowing sufficient time for the hydrolysis and fermentation to produce the fermentation end-product. EXAMPLE - No suitable example given.