possess a great metabolic versatility and grow heterotrophically on various carbon sources such as different sugars and peptides. Known sugar transporters in Archaea predominantly belong to ABC transport systems. Although several ABC transporters for sugar uptake have been characterized in the crenarchaeon , only one homologue of these transporters, the maltose/maltooligomer transporter, could be identified in the closely related Comparison of the transcriptome of grown on peptides alone and peptides in presence of D-xylose allowed for the identification of the ABC transporter for D-xylose and L-arabinose transport and to gain deeper insights into pentose catabolism under the respective growth conditions. The D-xylose/L-arabinose substrate binding protein (SBP) (Saci_2122) of the ABC transporter is unique in Archaea and shares more similarity to bacterial SBPs of the Carbohydrate Uptake Transporter-2 (CUT2) family than to any characterized archaeal one. The identified pentose transporter is the first CUT2 family ABC transporter analyzed in the domain of Archaea. Single gene deletion mutants of the ABC transporter subunits exemplified the importance of the transport system for D-xylose and L-arabinose uptake. Next to the transporter operon, enzymes of the aldolase-independent pentose catabolism branch were found to be upregulated in N-Z-Amine and D-xylose medium. The α-ketoglutarate semialdehyde dehydrogenase (KGSADH; Saci_1938) seemed not to be essential for growth on pentoses. However, the deletion mutant of the 2-keto-3-deoxyarabinoate/xylonate dehydratase (KDXD/KDAD; Saci_1939) was no longer able to catabolize D-xylose or L-arabinose suggesting the absence of the aldolase-dependent branch in Thermoacidophilic microorganisms are emerging model organisms for biotechnological applications as their optimal growth conditions resemble conditions used in certain biotechnologies such as plant waste industrial degradation. Because of its high genome stability is especially suited as a platform organism for such applications. For the use in (ligno)cellulose degradation, it was important to understand the pentose uptake and metabolism in This study revealed that only the aldolase-independent Weimberg pathway is required for growth of on D-xylose and L-arabinose. Moreover, employs a CUT2 ABC transporter for pentose uptake, which is more similar to bacterial than to archaeal ABC transporters. The identification of pentose inducible promoters will expedite the metabolic engineering of for its development into a platform organism for (ligno)cellulose degradation.

The thermophilic archaeon Sulfolobus acidocaldarius can use different carbon sources for growth, including the pentoses D-xylose and L-arabinose. In this study, we identified the activator XylR (saci_2116) responsible for the transcriptional regulation of the pentose transporter and pentose metabolizing genes in S. acidocaldarius. A xylR deletion mutant showed growth retardation on D-xylose/L-arabinose containing media and the lack of transcription of the respective ABC transporter. In contrast to so far used promoters for expression in S. acidocaldarius, the xylR responsive promoters have a very low background activity. Finally, two XylR dependent promoters next to the long-established maltose inducible promotor were used to construct a high-throughput expression vector system for S. acidocaldarius to efficiently clone and express proteins in S. acidocaldarius.