Reconstruction of the Central Carbohydrate Metabolism of Thermoproteus tenax by Use of Genomic and Biochemical Data

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Abstract
The hyperthermophilic, facultatively heterotrophic crenarchaeum Thermoproteus tenax was analyzed using a low-coverage shotgun-sequencing approach. A total of 1.81 Mbp (representing 98.5% of the total genome), with an average gap size of 100 bp and 5.3-fold coverage, are reported, giving insights into the genome of T. tenax. Genome analysis and biochemical studies enabled us to reconstruct its central carbohydrate metabolism. T. tenax uses a variant of the reversible Embden-Meyerhof-Parnas (EMP) pathway and two different variants of the Entner-Doudoroff (ED) pathway (a nonphosphorylative variant and a semiphosphorylative variant) for carbohydrate catabolism. For the EMP pathway some new, unexpected enzymes were identified. The semiphosphorylative ED pathway, hitherto supposed to be active only in halophiles, is found in T. tenax. No evidence for a functional pentose phosphate pathway, which is essential for the generation of pentoses and NADPH for anabolic purposes in bacteria and eucarya, is found in T. tenax. Most genes involved in the reversible citric acid cycle were identified, suggesting the presence of a functional oxidative cycle under heterotrophic growth conditions and a reductive cycle for CO2 fixation under autotrophic growth conditions. Almost all genes necessary for glycogen and trehalose metabolism were identified in the T. tenax genome.