SURFACE-CHARGE CHARACTERISTICS OF SMOOTH AND ROUGH SALMONELLA TYPHIMURIUM BACTERIA DETERMINED BY AQUEOUS TWO-PHASE PARTITIONING AND FREE ZONE ELECTROPHORESIS

Abstract

Aqueous biphasic partitioning of S. typhimurium S [smooth] and R [rought] bacteria in a system containing 6.2% (wt/wt) dextran 500 and 4.4% (wt/wt) poly(ethyleneglycol)6000 (PEG) was similar to the partition of the corresponding surface lipopolysaccharide (LPS). Further partition analysis with charged PEG showed that S bacteria and their LPS exposed very little charge, whereas R bacteria and their LPS showed a conspicuous negative charge at neutral pH. Free zone electrophoresis indicated that S bacteria have a much lower surface charge density than the R bacteria and accordingly a different surface structure. The physico-chemical properties of the bacterial surface seem to be determined to a greater extent by characteristics of the cell surface LPS.