EFFECT OF THE SURFACE-COMPOSITION OF MOTILE ESCHERICHIA-COLI AND MOTILE SALMONELLA SPECIES ON THE DIRECTION OF GALVANOTAXIS

We have reported that motile Escherichia coli K-12 placed in an electr ic field swims toward the anode but that motile Salmonella typhimurium strains swim toward the cathode, a phenomenon called galvanotaxis (J, Adler and W, Shi, Cold Spring Harbor Symp. Quant, Biol, 53:23-25, 198 8), In the present study, we isolated mutants with an altered directio n of galvanotaxis, By further analyses of these mutants and by examina tion of E. coli and Salmonella strains with altered cell surface struc ture, we have now established a correlation between the direction of g alvanotaxis and the surface structure of the cell: motile rough bacter ia (that is, those without O polysaccharide; for example, E, coli K-12 and S, typhimurium mutants of classes galE and rfa) swam toward the a node, whereas motile smooth bacteria (that is, those with O polysaccha ride; for example, wild-type S, typhimurium LT2) swam toward the catho de, However, smooth bacteria with acidic polysaccharide capsules (K1 i n E, coli and Vi in Salmonella typhi) swam toward the anode, Measureme nts of passive electrophoretic mobility of strains representative of e ach set were made. We propose that the different directions of galvano taxis of rough (or capsulate) bacteria and of smooth bacteria are expl icable if the negative electrophoretic mobility of flagellar filaments is less than that of rough bodies but greater than that of smooth bod ies.