Carbohydrate utilization patterns for the extremely thermophilic bacterium Caldicellulosiruptor saccharolyticus reveal broad growth substrate preferences

Co-utilization of hexoses and pentoses derived from lignocellulose is an attractive trait in microorganisms considered for consolidated biomass processing to biofuels. This issue was examined for the H2-producing, extremely thermophilic bacterium Caldicellulosiruptor saccharolyticus growing on individual monosaccharides (arabinose, fructose, galactose, glucose, mannose and xylose), mixtures of these sugars, as well as on xylan and xyloglucooligosacchrides. C. saccharolyticus grew at approximately the same rate (td approximately 95 min) and to the same final cell density (1-3 x 10(8) cells/ml) on all sugars and sugar mixtures tested. In the monosaccharide mixture, while simultaneous consumption of all monosaccharides was observed, not all were utilized to the same extent (fructose > xylose/arabinose > mannose/glucose/galactose). Transcriptome contrasts for monosaccharide growth revealed minimal changes in some cases (e.g., 31 ORFs changed >/= 2-fold for glucose vs. galactose) while substantial changes occurred for cases involving mannose (e.g., 363 ORFs >/= 2-fold for glucose vs. mannose). Evidence for catabolite repression was noted neither for growth on multi-sugar mixtures nor in the corresponding transcriptomes. Based on the whole-genome transcriptional response analysis and comparative genomics, carbohydrate specificities for transport systems could be proposed for most of the 24 putative carbohydrate ATP-binding cassette (ABC) transporters and single phosphotransferase system (PTS) identified in C. saccharolyticus. While most transporter genes responded to individual monosacchrides and polysaccharides, Csac_0692-0694 was up-regulated only in the monosaccharide mixture. The results here affirm the broad growth substrate preferences of C. saccharolyticus on carbohydrates representative of lignocellulosic biomass and suggest that this bacterium holds promise for biofuels applications