Genetik und Biochemie des Katabolismus von 5-Hydroxyectoin und Ectoin in dem marinen Bakterium Ruegeria pomeroyi DSS-3

The main focus of this study was on the catabolism of ectoines by the marine bacterium Ruegeria pomeroyi DSS-3. Based on the hypothesis of an enzymatic mechanism for the conversion of 5-hydroxyectoine to form ectoine and its subsequent degradation to L-aspartate, the physiological, genetic and biochemical requirements for the catabolism of ectoines were investigated. A chromosomal deletion of the enuR-uehABC-usp-eutABCDE-ssd-atf-operon in R. pomeroyi DSS-3 abolishes the utilization of these compounds as carbon and nitrogen sources. Bioinformatics showed that the phylogenetic distribution of ectoine consumers is restricted to the Proteobacteria and the genetic arrangement of the corresponding genes is not evolutinarily conserved. Using Northern Blot analyses and reporter gene fusions I was able to show that transcription of the catabolic ectoine/5-hydroxyectoine operon in R. pomeroyi is governed by a constitutive as well as a substrate inducible promoter. The transcriptional regulator EnuR belongs to the MocR/GabR-subfamily of transcriptional regulators and is a repressor as well as an activator for the operon. Its dependence on the cofactor pyridoxal-5'-phosphate and on two intermediates of the catabolic route was shown. In addition to EnuR the transcriptional activator AsnC, belonging to the 'feast-and-famine' family of transcriptional regulators, is coded for in the catabolic Ectoine-operon. The uptake and catabolism of alternative nitrogen sources in bacteria depend on the general nitrogen control (Ntr-) system. In R. pomeroyi DSS-3 the NtrXY two-component system is part of this Ntr system and as such, also involved in the regulation of Ectoin uptake and catabolism. Based on the biochemical and genetic analyses conducted here, a model for the transcriptional control of the catabolic gene cluster, comprising two transcriptional regulators and a two-component system of the general nitrogen control, was established.