The influence of low growth temperature on the amount of free R Lipopolysaccharide, on the expression of R-Core determinants and on O-Chain lengths in Salmonella S Forms

Abstract

Ten Salmonella strains belonging to five serological groups were cultivated both at 37 degrees C and close to their individual temperature minima at 12-14 degrees C and the composition of their cell wall lipopolysaccharides (LPS) was compared. When grown at low temperature, the proportion of unsubstituted (free) R-LPS in the total LPS moiety increased significantly in 6 strains, whereas in the other strains, no change or even a slight decrease in the R-LPS proportion was observed as judged from the analyses by SDS-PAGE. In the immunoblot, the R-LPSs from 9 out of 10 strains showed a modified reactivity against a set of specific Salmonella R antisera (anti-Ra, anti-Rb1, anti-Rb2, anti-Rc). In most cases, the decrease in Rb1 reactivity was paralleled by an increase in Rb2 reactivity and also by an increase in the total amount of free R-LPS. The electrophoretic mobility of free R-LPS was changed in 7 out of 10 strains, although the changes were not unidirectional. All changes occurred only in the range of the Ra-Rb1 chemotypes and no significant correlation to the serological grouping of the strains was evident. When grown at low temperature, the average number of O-repeating units was reduced in the majority of cases and in some cases, also the banding profile in SDS-PAGE in the S-LPS region was modified. The fatty acid spectra showed some changes which were in accordance with previous results, namely a decrease in the content of C-12:0 and C-16:0 and an increase in that of C-14:0 and C-16:1. The different influences of the growth temperature on the LPS biosynthesis of different Salmonella strains may be a result of the genetic diversity of this group of microorganisms.