4-aminobenzoic acid attenuates <i>Ralstonia solanacearum</i> virulence by suppressing quorum sensing system

Quorum sensing (QS) is widely involved in the regulation of the biological functions and pathogenic processes of bacteria in a cell density-dependent manner. The anthranilic acid signal is directly sensed by the receptor RaaR, a transcription regulator, to control the expression level of downstream target genes in Ralstonia solanacearum, thus affecting the QS signals generation and the bacterial virulence. Here, we reported that 4-Aminobenzoic acid (PABA), a structural analogue of anthranilic acid, not only significantly inhibited the production of extracellular polysaccharides (EPS), biofilm formation and motility of R. solanacearum, but also reduced the expression level of QS signaling molecules. We also found that PABA can directly bind to RaaR and prevented it from interacting with the promoters of target genes associated with the QS system and virulence of R. solanacearum. Point mutations in RaaR at residues F137 and I270 abolished the binding between RaaR and PABA, indicating that these two amino acid residues are likely critical for the interaction between RaaR and PABA. These findings indicated that PABA could be a candidate inhibitor of anthranilic acid signaling to interfere with the QS systems of R. solanacearum to attenuate the virulence. Together, our work presented a non-antibiotic-based treatment strategy and provided a theoretical basis for the development of novel antibacterial treatment.