Our project focuses on the compatible solutes ectoine and 5-hydroxyectoine and examines (i) their cellular accumulation as a cellular adjustment response to the perception of high osmolarity, and (ii) the detection of their presence in the environment and subsequent use as nutrients.
With respect to topic (i): we have identified several microorganisms that possess, associated with well-characterized ectoine/hydroxyectoine biosynthetic gene clusters, also novel types of import systems (EctI, EctU), exporters (EctE) and MscS-type excretion systems for ectoines. We will study the physiological roles of these ectoine/hydroxyectoine transport systems within the framework of the cellular adjustment process to osmotic stress in the marine bacterium Hyphomonas neptunium and in the soil bacterium Novosphingobium sp. strain LH128. Both microorganisms will also serve as model systems to study the osmotically controlled expression of the ectoine/hydroxyectoine synthesis and uptake gene clusters in these microorganisms at the genetic and molecular level. We will explore the precise role played by the widely preserved EctR regulatory protein in this process.
With respect to topic (ii): we have identified in the marine bacterium Ruegeria pomeroyi DSS-3 a cluster of 13 genes encoding an uptake system (TRAP-T) for ectoines and enzymes for their catabolism. Expression of this gene cluster is substrate inducible and controlled by EnuR, a member of the MocR/GabR sub-family of GntR-type transcriptional regulators. EnuR contains a covalently bound pyridoxal-5’-phosphate that reacts with an inducer generated through ectoine catabolism. We will study how: (a) externally provided ectoines are sensed by R. pomeroyi DSS-3, (b) how the internal inducer is generated through catabolism, and (c) how EnuR controls the activity of the substrate-inducible promoter of the ectoine/hydroxyectoine uptake and catabolic gene cluster. (d) We will further explore the possible transcriptional regulation of this gene cluster by additional nutritional cues; e.g., carbon and nitrogen availability.