Yersinia pseudotuberculosis is a facultative intracellular pathogen that migrates between two dissimilar habitats: the external environment, particularly in soil and water, and the human host, where it causes an intestinal infection known as yersiniosis. The transition between these habitats is tightly regulated by complex regulatory networks. Changes in the DNA topology of specific chromosomal regions (e.g. gene promoters) play an important role as well as global changes in DNA architecture mediated by nucleoid-associated proteins. The histone-like protein Fis is known as a transcriptional regulator found in many bacteria that regulates virulence factors and optimizes bacterial adaptation to different environments. Although the role of Fis has been described in various organisms, the regulatory networks specific for temperature fluctuations in Y. pseudotuberculosis have not yet been elucidated.

To gain a comprehensive insight into the global effects of Fis in Y. pseudotuberculosis at ambient and host body temperature, we conducted comparative RNA sequencing in the wild-type and a ∆fis mutant at 25 and 37 °C. Remarkably, the results uncovered more than 300 misregulated genes in ∆fis that were distributed among 14 functional gene categories. Furthermore, to identify specific DNA-binding sites of Fis, we performed chromatin affinity purification and sequencing (ChAP-Seq). These data in combination with phenotypic analyses show that the absence of Fis has significant physiological consequences in Yersinia. Most notably, the absence of Fis resulted in the upregulation of numerous virulence genes, including the main virulence regulator LcrF, and the loss of motility at 25 °C.

Overall, our data highlight the critical role of Fis in modulating Yersinia´s lifestyle by regulating genes involved in various cellular processes.