Occurrence and features of genes involved in xylose and xyloside utilization pathway in Firmicutes. Species with completely sequenced genomes in Bacilli/Clostridia classes are shown as rows. The presence of genes for the respective functional roles is shown by "+". Genes clustered on the chromosome are marked by the same background color. Candidate XylR regulon members are circled. Tentatively predicted functional roles are marked by asterisks. The number of species with xylose pathway divided by the total number of genomes in each taxonomic group is shown in parenthesis.