A method for converting lignocellulosic biomass material to a carboxylic acid comprising the step of contacting the lignocellulosic biomass material with a microbial culture for a period of time at an initial temperature and an initial pH, thereby producing an amount of a carboxylic acid; wherein the microbial culture comprises an extremely thermophilic bacteria strain selected from the group consisting of Caldicellulosiruptor sp. DIB041C, Caldicellulosiruptor sp. DIB087C, Caldicellulosiruptor sp. DIB103C, Caldicellulosiruptor sp. DIB104C, Caldicellulosiruptor sp. DIB107C, Caldicellulosiruptor sp. DIB101C, and Caldicellulosiruptor sp. DIB004C, and wherein the lignocellulosic biomass material is converted in a single step process as part of a consolidated bioprocessing (CBP) system.