In silico Analysis Reveals Distribution of Quorum Sensing Genes and Consistent Presence of LuxR Solos in the Pandoraea Species

The most common quorum sensing (QS) system in Gram-negative bacteria consists of signaling molecules called acyl-homoserine lactones (AHLs), which are synthesized by an enzyme AHL synthase (LuxI) and detected by a transcriptional regulator (LuxR) that are usually located in close proximity. However, many recent studies have also evidenced the presence of LuxR solos that are LuxR-related proteins in Proteobacteria that are devoid of a cognate LuxI AHL synthase. species are opportunistic pathogens frequently isolated from sputum specimens of cystic fibrosis (CF) patients. We have previously shown that strains possess QS activity. In this study, we examined the presence of QS activity in all type strains of species and acquired their complete genome sequences for holistic bioinformatics analyses of QS-related genes. Only four out of nine type strains ( , , and ) showed QS activity, and C8-HSL was the only AHL detected. A total of 10 canonical s with adjacent s were predicted by bioinformatics from the complete genomes of aforementioned species and publicly available genomes. No orphan was identified in any of the genomes. However, genes for two LuxR solos (LuxR2 and LuxR3 solos) were identified in all genomes (except two draft genomes with one LuxR solo gene), and was the only species that harbored no QS-related activity and genes. Except the canonical LuxR genes, LuxIs and LuxR solos of species were distantly related to the other well-characterized QS genes based on phylogenetic clustering. LuxR2 and LuxR3 solos might represent two novel evolutionary branches of LuxR system as they were found exclusively only in the genus. As a few solos were located in close proximity with prophage sequence regions in the genomes, we thus postulated that these solos could be transmitted into genus by transduction process mediated by bacteriophage. The bioinformatics approach developed in this study forms the basis for further characterization of closely related species. Overall, our findings improve the current understanding of QS in species, which is a potential pharmacological target in battling infections in CF patients.