TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Strain: The strain is capable of growing in a medium comprising a hydrolyzed lignocellulosic biomass material having a dry-matter content of at least 10-25% wt/wt. Preferably, the hydrolyzed lignocellulosic biomass material is selected from garden refuse, comminuted wood, straw, hay, fruit hulls, or seed hulls. The strain is capable of growing at or above 70degrees C. It is also capable of growing on galactose as the sole carbon source. The strain is capable of producing a fermentation product selected from an acid, an alcohol, a ketone, or hydrogen. Alcohol is selected from ethanol, butanol, propanol, methanol, propanediol, or butanediol. The acid is selected from lactic acid, proprionate, acetate, succinate, butyrate, or formate. Preferably, the ketone is acetone. One or more genes have been inserted, deleted, or substantially inactivated. A gene encoding lactate dehydrogenase (LDH) (EC 1.1.1.27) has been down-regulated or substantially inactivated by the deletion of the gene or by the mutation, deletion, or insertion of one or more amino acids in the gene. A gene encoding pyruvate ferredoxin oxidoreductase (EC 1.2.7.1) has been down-regulated or substantially inactivated by the mutation, deletion, or insertion of one or more amino acids in the gene. A gene encoding a hydrogenase or a hydrogenase subunit has been down-regulated or substantially inactivated by the mutation, deletion, or insertion of one or more amino acids in the gene. The gene encoding hydrogenase or a hydrogenase subunit is selected from (Fe)-hydrogenases or (NiFe)-hydrogenases (EC 1.6.5.3, EC 1.12.7.2, 1.12.99.6) such as NuoE, NuoF, NuoG, EchB, EchC, EchD, EchE, or EchF. A gene encoding an acetate kinase (EC 2.7.2.1) has been substantially inactivated by the mutation, deletion, or insertion of one or more amino acids in the gene. A gene encoding a phosphate acetyltransferase (EC 2.3.1.8) has been substantially inactivated by the mutation, deletion, or insertion of one or more amino acids in the gene. One or more genes encoding a polysaccharase have been inserted. Polysaccharase is selected from cellulases (EC 3.2.1.4); beta-glucanases, including glucan-1,3 beta-glucosidases (exo-1,3 beta-glucanases, EC 3.2.1.58), 1,4-beta-cellobiohydrolase (EC 3.2.1.91) and endo-1,3(4)-beta-glucanases (EC 3.2.1.6); xylanases, including endo-1,4-beta-xylanases (EC 3.2.1.8) and xylan 1,4-beta-xylosidase (EC 3.2.1.37); pectinases (EC 3.2.1.15); alpha-glucuronidase, alpha-L-arabinofuranosidase (EC 3.2.1.55), acetylesterase (EC 3.1.1.-), acetylxylanesterase (EC 3.1.1.72), alpha amylase (EC 3.2.1.1), beta-amylase (EC 3.2.1.2), glucoamylase (EC 3.2.1.3), pullulanase (EC 3.2.1.41), beta-glucanase (EC 3.2.1.73), hemicellulase, arabinosidase, mannanases including mannan endo-1,4-beta-mannosidase (EC 3.2.1.78) and mannan endo-1,6-alpha-mannosidase (EC 3.2.1.101), pectin hydrolase, polygalacturonase (EC 3.2.1.15), exopolygalacturonase (EC 3.2.1.67), or pectate lyase (EC 4.2.2.10). One or more genes encoding a pyruvate decarboxylase (EC 4.1.1.1) has been inserted. One or more genes encoding an alcohol dehydrogenase (EC 1.1.1.1, EC 1.1.1.2, EC 1.1.1.71, EC 1.1.99.8) have been inserted. The expression of one or more genes encoding an alcohol dehydrogenase has been increased. Preferred Method: Producing a fermentation product comprises culturing the strain. A fermentation process is performed under strict anaerobic conditions. The method is operated at temperature of 40-95degrees C, preferably 65-75degrees C. The fermentation process is a batch fermentation process or a continuous fermentation process. The fermentation product is selected from an acid, an alcohol, a ketone, or hydrogen. SPECIFIC MUTANTS - The T. mathranii strain is selected from BG1L1 (DSMZ Accession number 18283), BG1PF1 (DSMZ Accession number 18282), or BG1H1 (DSMZ Accession number 18281) (claimed).    EXAMPLE - A strain derived from BG1 was made by integration of a DNA fragment into the chromosome of BG1. The purified ppta32K plasmid, containing the thermostable kanamycin resistance gene flanked by the regions upstream and downstream from pfor, was linearized and electroporated into BG1, and positive recombinants were selected using the thermostable kanamycin resistance gene. Several independent clones were isolated and verified by PCR. PCR products from two clones were subsequently sequenced and were found to contain the kanamycin resistance cassette instead of the pfor genes. Five independent clones of BG1PF were grown in batch for two days with 5 g/l xylose as carbon source.