Genetic determination of the O antigens of Salmonella groups B (4,5,12) and C1(6,7)

M?kel?, P. Helena (University of Helsinki, Helsinki, Finland). Genetic determination of the O antigens of Salmonella groups B (4,5,12) and C(1) (6,7). J. Bacteriol. 91:1115-1125. 1966.-The genetic determination of the O antigens of Salmonella was studied by Hfr or F' crosses between strains of groups B (antigens 4,5,12) and C(1) (antigens 6,7). The main genetic determinants of the specificities 4 of group B and 7 of group C(1) behaved as alleles of one locus, called O or O-4/7. This is probably identical with O-4/9, responsible for the serological difference between groups B and D, and with the "rough" locus rouB. At least parts of the antigens 12 of group B and 6(2) of group C are determined at the same locus. The gene O-5 is closely linked to O-4/7, both mapping in the approximately 2 minutes distance between his and metG in the order his - O-4/7 - O-5 - metG. In crosses of group B donors with group C(1) recipients, a serologically new type, called semirough (SR), appeared in most recombinants that had inherited the O-4 allele of the group B donor. These SR forms are serologically intermediate between smooth and rough forms, showing poor stability in saline but possessing the specificities 4 and 12 and (some of them) 5. On the basis of previous biochemical studies, the hypothesis has been put forward that the side chains of their lipopolysaccharide are much shorter than normal group B side chains, probably containing only one repeating unit per side chain. A gene SR-4 responsible for the elongation of group B side chains beyond the first repeating unit was mapped between gal and try, group B and D bacteria being Sr-4(+), and group C being SR-4(-).