Investigation of the translation-initiation factor IF2 gene, infB, as a tool to study the population structure of Streptococcus agalactiae

The sequence of infB, encoding the prokaryotic translation-initiation facto r 2 (IF2), was determined in eight strains of Streptococcus agalactiae (gro up B streptococcus) and an alignment revealed limited intraspecies diversit y within S. agalactiae. The amino acid sequence of IF2 from S. agalactiae a nd from related species were aligned and revealed an interspecies conserved central and C-terminal part, and an N-terminal part that is highly variabl e in length and amino acid sequence. The diversity and relationships in a c ollection of 58 genetically distinct strains of S. agalactiae were evaluate d by comparing a partial sequence of infB. A total of six alleles were dete cted for the region of infB analysed. The alleles correlated with the separ ation of the same strains of S. agalactiae into major evolutionary lineages , as shown in previous work. The partial sequences of infB were furthermore used in phylogenetic analyses of species closely related to S. agalactiae, yielding an evolutionary tree which had a topology similar to a tree const ructed using 16S rRNA sequences from the same species.