Abstract
The degradation of the pentoses d-xylose, l-arabinose and d-ribose in the domain of archaea, in Haloferax volcanii and in Haloarcula and Sulfolobus species, has been shown to proceed via oxidative pathways to generate α-ketoglutarate. Here, we report that the haloarchaeal Halorhabdus species utilize the bacterial-type non-oxidative degradation pathways for pentoses generating xylulose-5-phosphate. The genes of these pathways are each clustered and were constitutively expressed. Selected enzymes involved in d-xylose degradation, xylose isomerase and xylulokinase, and those involved in l-arabinose degradation, arabinose isomerase and ribulokinase, were characterized. Further, d-ribose degradation in Halorhabdus species involves ribokinase, ribose-5-phosphate isomerase and d-ribulose-5-phosphate-3-epimerase. Ribokinase of Halorhabdus tiamatea and ribose-5-phosphate isomerase of Halorhabdus utahensis were characterized. This is the first report of pentose degradation via the bacterial-type pathways in archaea, in Halorhabdus species that likely acquired these pathways from bacteria. The utilization of bacterial-type pathways of pentose degradation rather than the archaeal oxidative pathways generating α-ketoglutarate might be explained by an incomplete gluconeogenesis in Halorhabdus species preventing the utilization of α-ketoglutarate in the anabolism.
Highlights
The pentoses d-xylose, l-arabinose and d-ribose are abundant in nature being part of hemicellulose material of plants and as component of ribonucleotides
Genome analyses indicate that Halorhabdus utahensis unlike other haloarchaea contains genes encoding putative enzymes of the classical pathways of d-xylose and l-arabinose degradation reported for most bacteria (Anderson et al 2011)
D-ribose degradation in H. utahensis and Halorhabdus tiamatea and the enzymes involved were studied revealing the operation of the bacterial-type pathway of D-ribose degradation
Summary
The pentoses d-xylose, l-arabinose and d-ribose are abundant in nature being part of hemicellulose material of plants and as component of ribonucleotides. We report transcription of selected genes of d-xylose and l-arabinose degradation in H. utahensis and the characterization of their encoded enzymes. We found that d-ribose is degraded in H. utahensis and Halorhabdus tiamatea to xylulose-5-phosphate by the bacterial pathway involving the enzymes ribokinase, ribose-5-phosphate isomerase and d-ribulose-5-phosphate3-epimerase.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
