Hexose degradation pathways and their transcriptional regulation in halophilic archaea

• Applicant: Professor Dr. Peter Schönheit
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 286542984

Haloferax volcanii utilizes the hexoses D-glucose and D-galactose and the deoxyhexose L-rhamnose as carbon and energy source. First studies of our group indicate that glucose is degraded via a semiphosphorylative Entner-Doudoroff (spED) pathway and D-galactose via a De Ley-Doudoroff (DD) pathway. The transport of glucose and galactose, several key enzymes of the degradation pathways, and their transcriptional regulation have not been studied in detail so far. Also, the degradation of L-rhamnose in haloarchaea has not been investigated so far. Adjacent to the gene of glucose dehydrogenase, the first enzyme of glucose degradation, we identified a gene encoding a putative transcriptional regulator PyrE1, which is homologous to the unusual transcriptional regulators of purine- and pyrimidine metabolism of few gram-positive bacteria. Further, we have identified in the gene cluster of galactose degradation pathway - a putative IclR like transcriptional regulator. First studies indicate a function of both regulators as transcriptional activators of glucose and galactose degradation pathways, respectively. In the galactose gene cluster we identified an ABC transporter, likely involved in galactose transport. Haloarcula marismortui also contained - in genomic neighbourhood of glucose dehydrogenase gene, a PyrE1 homologous transcriptional regulator and an ABC transporter, likely involved in glucose transport. During growth of H. volcanii on L-rhamnose we found an inducible L-rhamnose dehydrogenase activity indicating the operation of a non phosphorylative L-rhamnose degradation pathway. In the genome of H. volcanii we identified two gene clusters encoding hypothetical rhamnose degradation pathways each including genes for ABC transporter and IclR like transcriptional regulators. In the planned grant proposal we will investigate transport, the degradation pathways and their transcriptional regulation of D-glucose, D-galactose and L-rhamnose in haloarchaea. The involvement of ABC transporters in sugar transport will be analysed using deletion mutants and by characterization of the sugar binding proteins. The key enzymes of sugar degradation pathways and the transcriptional regulators PyrE1 and IclR in haloarchaea will be studied in detail. The studies will contribute to the understanding of unusual sugar degradation pathways in haloarchaea and of novel types of transcriptional regulators in the domain of archaea.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Ulrike Johnsen