Contribution of the Sensor Histidine Kinases PhcS and VsrA to the Quorum Sensing of <i>Ralstonia pseudosolanacearum</i> Strain OE1-1

The soilborne Gram-negative phytopathogenic beta-proteobacterium <i>Ralstonia pseudosolanacearum</i> strain OE1-1 produces methyl 3-hydroxymyristate (3-OH MAME) as the quorum sensing (QS) signal by the methyltransferase PhcB and senses the chemical, activating the LysR family transcriptional regulator PhcA, which regulates the QS-dependent genes responsible for QS-dependent phenotypes including virulence. The sensor histidine kinases PhcS and VsrA are reportedly involved in the regulation of QS-dependent genes. To elucidate the function of PhcS and VsrA in the active QS, we generated the <i>phcS-</i>deletion and <i>vsrA</i>-deletion mutants, which exhibited weak changes to their QS-dependent phenotypes including virulence. The <i>phcS</i> and <i>vsrA</i>-deletion mutant (Δ<i>phcS</i>/<i>vsrA</i>) had significant changes in its QS-dependent phenotypes and was nonvirulent, similar to the <i>phcA</i>-deletion mutant. The mutant (PhcS-H230Q) with a substitution of histidine to glutamine at amino acid position 230 in PhcS but not the mutant (VsrA-H256Q) with a substitution of histidine to glutamine at amino acid position 256 in VsrA exhibited significant changes in QS-dependent phenotypes and lost virulence. The transcriptome analysis with RNA-sequencing revealed significant alterations to the expression of QS-dependent genes in the Δ<i>phcS</i>/<i>vsrA</i> and PhcS-H230Q but not VsrA-H256Q, similar to the <i>phcA</i>-deletion mutant. The exogenous 3-OH MAME application led to a significantly enhanced QS-inducible major exopolysaccharide EPS I production of the strain OE1-1 and <i>phcB</i>-deletion mutant but not Δ<i>phcS</i>/<i>vsrA</i> and PhcS-H230Q. Collectively, results of the present genetic study suggested that PhcS contributes to QS along with VsrA and that histidine at amino acid position 230 of PhcS is required for 3-OH MAME sensing, thereby influencing QS-dependent phenotypes including virulence of the strain OE1-1. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.