13C nuclear magnetic resonance studies on selectively labeled bacterial biofilms

Bacterial biofilms of Pseudomonas aeruginosa selectively labeled by introduction of 2-13C-glycerol was studied by solid-state and high-resolution nuclear magnetic resonance. The 13C nuclei were mainly integrated into mannuronate and guluronate, the two monomer units forming the bacterial alginate. The signal for the C5 position of the mannuronate, which was easily identified and well separated from other peaks, was analyzed for molecular mobility. The result indicated a high degree of motional freedom within the molecular network of the alginate. Despite the fact that the alginate was part of a solid aqueous gel phase, the reorientation mechanism of the monomer units came close to isotropic tumbling. Solid-state spectra of biofilms labeled in the described manner may serve as a valuable tool for noninvasive analyses of molecular mobility of the alginate component under various influences, thereby revealing important structural information. In addition, the effect of a monovalent electrolyte (LiCl) on the molecular mobility of alginate fragments in an aqueous solution was studied by determining the spin-lattice relaxation times, line widths and line shapes under variations of the ion concentration. The presence of ions accelerated overall motions but left rapid local motions virtually unaffected.