Das marine Dimethylpropionat als protektives Osmolyt und die Evolutionverwandter ABC Transporter für die Aufnahme von kompatiblen Soluten

The tertiary sulfonium compound dimethylsulfoniopropionate (DMSP) is produced in vast amounts by marine macroalgae and phytoplankton and also by a restricted number of plants. These organisms used DMSP as a stress protectant and upon cell lysis or viral infection DMSP can be released into open ocean water. It is an integral constituent of the global sulfur cycle and DMSP is the precursor of the climatically active gas DMS. Members of the genus Bacillus can colonize a great variety of ecosystems and certainly have access to DMSP. In B. subtilis the protection against abiotic stress are well characterized, but it is unknown whether it catabolizes DMSP and/or can derived stress protection from DMSP. With a well characterized set of B. subtilis strains has been found, that DMSP is not a nutrient for B. subtilis, but it served as an excellent stress protectant against salt, cold and heat challenges. Also its natural selenium and synthetetic derivatives served as osmostress and partially cold stress protectant, but DMSP was the more effective stress protectant. DMSP and its derivatives influenced the size of the osmostress-adaptive proline pool and reduced the salt-induced expression of the opuA operon. DMSP uptake by osmotically and temperaturestressed B. subtilis cells are mediated by the ABC transporter OpuA and OpuC. The OpuC transporter was the main transporter not only for DMSP uptake, but also for its natural and synthetic derivatives. The ABC transporter OpuC is a remarkable osmolyte import system, because its substrat specificity is extremely broad. In contrast, the related OpuB transporter exhibited transport activity only for choline. The OpuB transporter were developed due a gene dublication event out of the OpuC transporter. With bioinformatics assessment, site-directed mutagenesis and crystallographic studies were the molecular determents of the ligand binding-site characterized.