Temporal regulation of Salmonella pathogenicity Island 1 (SPI-1) hilA by Hfq in Salmonella enterica serovar typhimurium

Hfq is a global regulatory RNA-binding protein abundant in many bacteria. In terms of virulence regulation in Salmonella, Hfq binds to and stabilizes the mRNA of hilD, a master regulator of Salmonella pathogenicity island 1 (SPI-1), and Hfq activates SPI-1 gene transcription during the late exponential-growth phase. In contrast to the positive roles of Hfq in SPI-1 regulation, we observed that the absence of Hfq increased the expression of SPI-1 regulators, including HilA and InvF, during the late stationary phase. This result suggests that Hfq has pleiotropic functions, controlling SPI-1 positively or negatively depending on the growth conditions.