NOVELTY - Isolated Caldicellulosiruptor acetigenus cell comprising a 16S recombinant DNA (rDNA) sequence, which is at least 99%, preferably 100% identical to SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6 or SEQ ID NO: 7, is new.    USE - The isolated Caldicellulosiruptor acetigenus cell is useful for producing fermentation product including acid, alcohol, hydrogen, ethanol, lactic acid and their salts or esters, where the alcohol is ethanol, butanol, propanol, methanol, propanediol and butanediol, and the acid is lactic acid, propionic acid, acetic acid, succinic acid, malic acid, butyric acid and formic acid, from lignocellulosic biomass.    ADVANTAGE - The isolated Caldicellulosiruptor acetigenus cell provides fermentation products with high yield and low product inhibition at an elevated temperature, in more economical and feasible manner.    DETAILED DESCRIPTION - Isolated Caldicellulosiruptor acetigenus cell comprising a 16S recombinant DNA (rDNA) sequence, which is at least 99%, preferably 100% identical to SEQ ID NO: 1 (a 1396 amino acid sequence fully defined in the specification), SEQ ID NO: 2 (a 1580 amino acid sequence fully defined in the specification), SEQ ID NO: 3 (a 1481 amino acid sequence fully defined in the specification), SEQ ID NO: 4 (a 1212 amino acid sequence fully defined in the specification), SEQ ID NO: 5 (a 1253 amino acid sequence fully defined in the specification), SEQ ID NO: 6 (a 1255 amino acid sequence fully defined in the specification) or SEQ ID NO: 7 (a 1446 amino acid sequence fully defined in the specification). INDEPENDENT CLAIMS are included for: (1) an isolated strain of the genus Caldicellulosiruptor acetigenus, comprising Caldicellulosiruptor acetigenus DIB041C, deposited as DSM 25771, Caldicellulosiruptor acetigenus DIB087C, deposited as DSM 25772, Caldicellulosiruptor acetigenus DIB103C, deposited as DSM 25773, Caldicellulosiruptor acetigenus DIB104C, deposited as DSM 25774, Caldicellulosiruptor acetigenus DIB107C, deposited as DSM 25775, Caldicellulosiruptor acetigenus DIB101C, deposited as DSM 25178 and Caldicellulosiruptor acetigenus DIB004C, deposited as DSM 25177, microorganism derived from it, progenies and theirs mutant; (2) a composition for converting lignocellulosic biomass comprising the cell and/or the strain; and (3) a microbial culture comprising the cell and/or the strain.