Phylogeny, Synteny, and Distribution of Type III Secretion Systems in Burkholderia cenocepacia: A Closer Look Into Host Span.

Type III secretion systems (T3SS) have been described in many Gram-negative bacteria, including the human opportunistic pathogen Burkholderia cenocepacia, originally described in association with plants. The present work aimed to identify T3SS genes in a group of genomes of isolates from different sources, to gain insight into their role in the life cycle and host association of B. cenocepacia. Comparative and phylogenetic analyses were used to investigate the distribution, evolution, variability, and synteny of the T3SS genes within 48 genomes of B. cenocepacia. Only one genome, from a human clinical isolate, lacked T3SS genes. These results revealed 9 different clusters of T3SS genes within B. cenocepacia, all lacking an annotated needle protein gene (sctF) within the T3SS clusters. Interestingly, a CDS encoding a putative SctF was found outside the main T3SS gene clusters, which is highly conserved in all analyzed genomes. Taken together, these results suggest that the T3SS gene clusters seem to have been independently acquired and may play a pivotal role in pathogenicity, host range determination, and niche adaptation.