The Fis Nucleoid Protein Negatively Regulates the Phase Variation fimS Switch of the Type 1 Pilus Operon in Enteropathogenic Escherichia coli

• Published in: Frontiers in microbiology 2022-04, Vol.13, p.882563-882563
• Main Authors: Saldaña-Ahuactzi, Zeus, Soria-Bustos, Jorge, Martínez-Santos, Verónica I, Yañez-Santos, Jorge A, Martínez-Laguna, Ygnacio, Cedillo-Ramirez, María Lilia, Puente, José L, Girón, Jorge A
• Format: Article
• Language: English
• Subjects: EPEC; fimS switch; Fis; Microbiology; phase variation; type 1 pilus
• ISSN: 1664-302X; 1664-302X
• DOI: 10.3389/fmicb.2022.882563

In the expression of type 1 pili (T1P) is determined by the site-specific inversion of the ON-OFF switch located immediately upstream of major fimbrial subunit gene . Here we investigated the role of virulence (Ler, GrlR, and GrlA) and global regulators (H-NS, IHF, and Fis) in the regulation of the switch in the human enteropathogenic (EPEC) O127:H6 strain E2348/69. This strain does not produce detectable T1P and PCR analysis of the switch confirmed that it is locked in the OFF orientation. Among the regulator mutants analyzed, only the ∆ mutant produced significantly high levels of T1P on its surface and yielded high titers of agglutination of guinea pig erythrocytes. Expression analysis of the , , and promoters using transcriptional fusions indicated that only P activity is enhanced in the absence of Fis. Collectively, these data demonstrate that Fis is a negative regulator of T1P expression in EPEC and suggest that it is required for the FimE-dependent inversion of the switch from the ON-to-OFF direction. It is possible that a similar mechanism of T1P regulation exists in other intestinal and extra-intestinal pathogenic classes of .