D-xylose degradation pathway in the halophilic archaeon Haloferax volcanii.
The pathway of D-xylose degradation in archaea is unknown. In a previous study we identified in Haloarcula marismortui the first enzyme of xylose degradation, an inducible xylose dehydrogenase (Johnsen, U., and Schönheit, P. (2004) J. Bacteriol. 186, 6198-6207). Here we report a comprehensive study of the complete D-xylose degradation pathway in the halophilic archaeon Haloferax volcanii. The analyses include the following: (i) identification of the degradation pathway in vivo following (13)C-labeling patterns of proteinogenic amino acids after growth on [(13)C]xylose; (ii) identification of xylose-induced genes by DNA microarray experiments; (iii) characterization of enzymes; and (iv) construction of in-frame deletion mutants and their functional analyses in growth experiments. Together, the data indicate that D-xylose is oxidized exclusively to the tricarboxylic acid cycle intermediate alpha-ketoglutarate, involving D-xylose dehydrogenase (HVO_B0028), a novel xylonate dehydratase (HVO_B0038A), 2-keto-3-deoxyxylonate dehydratase (HVO_B0027), and alpha-ketoglutarate semialdehyde dehydrogenase (HVO_B0039). The functional involvement of these enzymes in xylose degradation was proven by growth studies of the corresponding in-frame deletion mutants, which all lost the ability to grow on d-xylose, but growth on glucose was not significantly affected. This is the first report of an archaeal D-xylose degradation pathway that differs from the classical D-xylose pathway in most bacteria involving the formation of xylulose 5-phosphate as an intermediate. However, the pathway shows similarities to proposed oxidative pentose degradation pathways to alpha-ketoglutarate in few bacteria, e.g. Azospirillum brasilense and Caulobacter crescentus, and in the archaeon Sulfolobus solfataricus.
Johnsen
Ulrike
U
Institut für Allgemeine Mikrobiologie, Christian-Albrechts-Universität Kiel, D-24118 Kiel, Germany.
Dambeck
Michael
M
Zaiss
Henning
H
Fuhrer
Tobias
T
Soppa
Jörg
J
Sauer
Uwe
U
Schönheit
Peter
P
D000595:Amino Acid Sequence; D002457:Cell Extracts; D019766:Genes, Archaeal; D019622:Haloferax volcanii / Q000166:cytology / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D006836:Hydro-Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D017384:Sequence Deletion; D014994:Xylose / Q000378:metabolism* / Q000494:pharmacology
D002457:Cell Extracts; D014994:Xylose; D006836:Hydro-Lyases