ELASTIC PROPERTIES OF THE CELL-WALL OF MAGNETOSPIRILLUM GRYPHISWALDENSE INVESTIGATED BY ATOMIC-FORCE MICROSCOPY

Gram-negative magnetic bacteria of the species Magnetospirillum gryphi swaldense were investigated by atomic force microscopy (AFM) in buffer solution. The highly positively charged silane trimethoxysilyl-propyl -diethylenetriamine was used to coat cover glass surfaces for adsorpti on of the bacteria. The resulting bacterial surface was flat, and in m ost cases it was not possible to resolve any structures. Force curves were obtained for the substrate and for the bacteria while scanning la terally, in a technique called ''force mapping''. To obtain a quantita tive measure for the elasticity of the cell wall the contribution of t he internal osmotic pressure had to be estimated. There was no detecta ble change in the observed elastic response when the osmolarity of the surrounding medium was changed; this showed that the elastic response was due to the cell wall. It was thus possible to determine the effec tive compressibility of the cell wall, which was about 42 mN/m.