MAPPING CELL-WALL POLYSACCHARIDES OF LIVING MICROBIAL-CELLS USING ATOMIC-FORCE MICROSCOPY

Functionalized atomic force microscope tips were used to sense specifi c forces of interaction between ligand-receptor pairs and to map the p ositions of polysaccharides on a living microbial cell surface. Gold-c oated tips were functionalized with concanavalin A using a cross-linke r with a spacer arm of 15.6 Angstrom. It was possible to measure the b inding force between concanavalin A and mannan polymers on the yeast ( Saccharomyces cerevisiae) cell surface. This force ranged from 75 to 2 00 pN. The shape of the force curve indicated that the polymers were p ulled away from the cell surface for a fairly long distance that somet imes reached several hundred nanometres. The distribution of mannan on the cell surface was mapped by carrying out the force measurement in the force volume mode of atomic force microscopy (AFM). During the mea surement, the maximum cantilever deflection after contact between the tip and the sample was kept constant at 10 nm using trigger mode to ke ep the pressing force on the sample surface as gently as possible at a force of 180 pN. This regime was used to minimize the non-specific ad hesion between the tip and the cell surface. Specific molecular recogn ition events took place on specific areas of the cell surface that cou ld be interpreted as reflecting a non-uniform distribution of mannan o n the cell surface. (C) 1997 Academic Press.