Untersuchung schwacher Wechselwirkungen innerhalb von Biofilmen mittels 13C-Spektroskopie
The investigation of weak interactions within biofilms of P. aeruginosa SG81 and its isolates (EPS, alginate) show a strong relationship between the mechanical properties of the biofilm and the aqueous solvent (e.g. pH value, ionic strengh, presence of mono- or bivalent cations). Comparing the C-5 resonance lines of 13C- NMR spectra within a Li+ - concentration series with simulated spectra, a rapid decrease of the correlation time even at low ionic strengh is clearly observed. Therefore, the addition of monovalent counterions reduces the intramolecular electrostatic interactions between adjacent carboxyl groups within the polysaccharide. This results in a further entanglement of the macromolecule. Regarding bivalent counterions, significant differences with regard to the degree of interactions of the examined species (Mg2+, Ca2+) with the alginate could be observed. Mg2+ ions show rather weak and non-specific interactions towards bacterial alginates, whereas Ca2+ ions indicate a specific binding behaviour. In addition to this, a new model for the binding of Ca2+ ions to bacterial alginate was proposed on the basis of NMR- measurements in the presence of paramagnetic ions (Mn2+). Furthermore, the effects of stress factors (nutrient or oxygen depletion)on biofilm structure have been investigated in a long-term in vivo experiment. It was shown, that the mechanical stability of a biofilm under these environmental conditions is rapidly decreased due to the release of alginate lyase.