ICETh1 and ICETh2, two interdependent mobile genetic elements in Thermus thermophilus transjugation

Summary Cell to cell DNA transfer between Thermus thermophilus , or transjugation, requires the natural competence apparatus (NCA) of the recipient cell and a DNA donation machinery in the donor. In T . thermophilus HB27, two mobile genetic elements with functional similarities to Integrative and Conjugative Elements (ICEs) coexist, ICETh1 encoding the DNA transfer apparatus and ICETh2, encoding a putative replication module. Here, we demonstrate that excision and integration of both elements depend on a single tyrosine recombinase encoded by ICETh2, and that excision is not required but improves the transfer of these elements to a recipient cell. These findings along with previous results suggest that ICETh1 and ICETh2 depend on each other for spreading among T . thermophilus by transjugation.