Mutational analysis of Burkholderia thailandensis quorum sensing and self-aggregation

Acyl-homoserine lactone (acyl-HSL) quorum-sensing signaling is common to many Proteobacteria. Acyl-HSLs are synthesized by the LuxI family of synthases, and the signal response is mediated by members of the LuxR family of transcriptional regulators. Burkholderia thailandensis is a member of a closely related cluster of three species, including the animal pathogens Burkholderia mallei and Burkholderia pseudomallei. Members of this group have similar luxI and luxR homologs, and these genes contribute to B. pseudomallei and B. mallei virulence. B. thailandensis possesses three pairs of luxI-luxR homologs. One of these pairs, BtaI2-BtaR2, has been shown to produce and respond to 3OHC ₁₀-HSL and to control the synthesis of an antibiotic. By using a markerless-exhange method, we constructed an assortment of B. thailandensis quorum-sensing mutants, and we used these mutants to show that BtaI1 is responsible for C₈-HSL production and BtaI3 is responsible for 3OHC₈-HSL production. We also show that a strain incapable of acyl-HSL production is capable of growth on the same assortment of carbon and nitrogen sources as the wild type. Furthermore, this mutant shows no loss of virulence compared to the wild type in mice. However, the wild type self-aggregates in minimal medium, whereas the quorum-sensing mutant does not. The wild-type aggregation phenotype is recovered by addition of the BtaI1-R1 HSL signal C₈-HSL. We propose that the key function of the BtaR1-BtaI1 quorum-sensing system is to cause cells to gather into aggregates once a sufficient population has been established.