Expansion of the Group B <i>Streptococcus</i> serotype repertoire via gene acquisition from other streptococcal species

Capsular polysaccharide (CPS) is a key virulence factor that aids group B <i>Streptococcus</i> (GBS) in colonization and pathogenicity in humans. The major human vaccine candidate against GBS is a CPS-based vaccine including six serotypes. In addition to the four non-vaccine serotypes, intra- and interspecies horizontal gene transfer (HGT) could create GBS strains with novel capsule structures, potentially leading to vaccine escape. Here, we describe a key gene, <i>cpsR</i>, in the production of GBS serotype VIII and the complementation of its function by orthologs from other streptococci. Our work demonstrates GBS's ability to utilize genes from other streptococci to produce functional capsular polysaccharide. HGT could generate further capsule diversity beyond the 10 current serotypes, potentially increasing the number of strains capable of vaccine escape. Surveillance for such events is warranted.