Coutilization 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
xylogluco-oligosacchrides. C. saccharolyticus grew at approximately the same rate (td, 95 min) and to the same
final cell density (1 108 to 3 108 cells/ml) on all sugars and sugar mixtures tested. In the monosaccharide
mixture, although 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., 32 open reading frames [ORFs]
changed >2-fold for glucose versus galactose), while substantial changes occurred for cases involving mannose
(e.g., 353 ORFs changed >2-fold for glucose versus mannose). Evidence for catabolite repression was not noted
for either growth on multisugar mixtures or 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 transporters and single
phosphotransferase system identified in C. saccharolyticus. Although most transporter genes responded to
individual monosaccharides and polysaccharides, the genes Csac_0692 to Csac_0694 were upregulated only in
the monosaccharide mixture. The results presented here affirm the broad growth substrate preferences of C.
saccharolyticus on carbohydrates representative of lignocellulosic biomass and suggest that this bacterium
holds promise for biofuel applications.