The Response Regulator FlmD Regulates Biofilm Formation in Comamonas testosteroni through the Transcriptional Activator SoxR.

Biofilm formation is a survival strategy by which microorganisms adapt to environmental challenges. It is regulated by various signals, such as the second messenger c -di-GMP. We previously found that the Flm chemosensory pathway could respond to chemical signals and regulate biofilm formation. This regulation is independent of c -di-GMP. A previous study revealed that the response regulator FlmD is involved in biofilm formation; however, how chemical signals are transmitted downstream of FlmD remained unclear. In the present study, transcriptome analysis and gel shift assay reveal that SoxR, a transcriptional activator of the efflux transporter acrAB-tolC operon, mediates the downstream signaling of FlmD. Phosphorylated FlmD interacts with SoxR and disrupts the interaction between SoxR and the acrAB-tolC operon. It causes a decrease in the expression of acrAB-tolC operon. The downregulation of acrA , acrB , or tolC gene expression results in making less biofilm formation. In conclusion, we identified that the transcription regulator SoxR plays a role in the c -di-GMP independent regulation of biofilm formation in Comamonas testosteroni .