Deoxyribonucleic acid restriction and modification systems in Salmonella: chromosomally located systems of different serotypes

Abstract

Using 4 different phages, Salmonella strains representing 85 different serotypes were examined to determine their restriction-modification phenotype. They fell into 1 of 3 groups on this basis; group 1, those which lacked the common LT system; group 2, those in which only the LT system could be recognized; and group 3, those which possessed the LT system and at least 1 other system shown with some serotypes to be closely linked to serB. The specificity of the serB-linked restriction-modification system was unique for each serotype, but different strains of the same serotype expressed the same specificity. Two of the systems behaved in genetic crosses as functional alleles of the S. typhimurium SB system. These serB-linked restriction-modification systems may constitute a large multiallelic series of genes extending throughout the Salmonella genus and Escherichia coli. The division of the Salmonella into the 3 restriction-modification groups may be significant in defining a biological grouping of the different serotypes within the genus which may ultimately be useful in describing the Salmonella spp. The genetic relatedness between the genes of some of the Salmonella restriction-modification systems with those of the E. coli systems showed that the restriction endonucleases produced by the Salmonella serB-linked systems are of type 1. Determination of the nucleotide sequences of the recognition sites of the restriction endonucleases of selected Salmonella system should further the understanding of specificity with these enzymes.