Comparative analysis of quorum-sensing systems that control pathogenicity in three phylogenetic groups of Pseudomonas isolated from tomato pith necrosis in Japan.

Tomato pith necrosis (TPN) is a common disease worldwide. In this study, we investigated the relationship between acylhomoserine lactone (AHL)-mediated quorum sensing and pathogenicity in 21 TPN isolates, which were classified into three groups: Group 1 (Pseudomonas corrugata), Group 2 (Pseudomonas mediterranea), and Group 3 (novel taxonomic group). All strains produced N-hexanoyl-l-homoserine lactone as the dominant AHL molecule. Phylogenetic analyses revealed high conservation of quorum-sensing genes among the three groups, with nearly identical sequences and arrangements. Whole genome sequencing of the Group 3 strain MAFF 730105 revealed the presence of a Type III secretion system gene cluster, similar to well-known plant pathogens. Although quorum sensing influences virulence, its impact is limited, and some virulence factors may be constitutive or regulated independently. These results suggest that quorum sensing contributes to TPN symptoms; however, additional factors and regulatory mechanisms are involved in the pathogenicity of TPN isolates.