Regulatory Cross Talk between Motility and Interbacterial Communication in Salmonella enterica Serovar Typhimurium

FliA is a broadly conserved a factor that directs transcription of genes involved in flagellar motility. We previously identified FIiA-transcribed genes in Escherichia coli and Salmonella enterica serovar Typhimurium, and we showed that E. coli FliA transcribes many unstable, noncoding RNAs from intragenic promoters. Here, we show that FliA in S. Typhimurium also directs the transcription of large numbers of unstable, noncoding RNAs from intragenic promoters, and we identify two previously unreported FliA-transcribed protein-coding genes. One of these genes, sdiA, encodes a transcription factor that responds to quorum-sensing signals produced by other bacteria. We show that FIiA-dependent transcription of sdiA is required for SdiA activity, highlighting a regulatory link between flagellar motility and intercellular communication. IMPORTANCE Initiation of bacterial transcription requires association of a sigma factor with the core RNA polymerase to facilitate sequence-specific recognition of promoter elements. FIiA is a widely conserved sigma factor that directs transcription of genes involved in flagellar motility. We previously showed that Escherichia coli FIiA transcribes many unstable, noncoding RNAs from promoters within genes. Here, we demonstrate the same phenomenon in Salmonella Typhimurium. We also show that S. Typhimurium FliA directs transcription of the sdiA gene, which encodes a transcription factor that responds to quorum-sensing signals produced by other bacteria. FIiA-dependent transcription of sdiA is required for transcriptional control of SdiA target genes, highlighting a regulatory link between flagellar motility and intercellular communication.