Two-Component Signal Transduction Systems in the Human Pathogen Streptococcus agalactiae

Streptococcus agalactiae (group B Streptococcus [GBS)) is an important cause of invasive infection in newborns, maternal women, and older individuals with underlying chronic illnesses. GBS has many mechanisms to adapt and survive in its host, and these mechanisms are often controlled via two-component signal transduction systems. In GBS, more than 20 distinct two-component systems (TCSs) have been classified to date, consisting of canonical TCSs as well as orphan and atypical sensors and regulators. These signal transducing systems are necessary for metabolic regulation, resistance to antibiotics and antimicrobials, pathogenesis, and adhesion to the mucosal surfaces to colonize the host. This minireview discusses the structures of these TCSs in GBS as well as how selected systems regulate essential cellu- lar processes such as survival and colonization. GBS contains almost double the number of TCSs compared to the closely related Streptococcus pyogenes and Strepto- coccus pneumoniae, and while research on GBS TCSs has been increasing in recent C years, no comprehensive reviews of these TCSs exist, making this review especially relevant.