Work

Regulation of PL fimbriae ( plf ) and role of PlfB as a negative regulator during avian pathogenic Escherichia coli infection in turkeys

Year: 2026

Type: preprint

Abstract: Little is currently known about the regulation of PL fimbriae produced by some pathogenic E. coli strains. We identified PlfB, a transcriptional regulator of the PapB family, as a negative regulator of PL fimbriae (Plf). Deletion of plfB significantly increased plfA transcription and Plf production. PlfB bound specifically to the plfA promoter region. Using a P plfA – lux reporter system, the deletion of plfB caused sustained and increased expression across serial passages. Global regulatory genes such as lrp , argR , and hns were also implicated in regulation of plf expression. Loss of lrp or argR decreased plf expression, suggesting these regulators positively regulate PL fimbriae. By contrast, loss of hns increased levels of plf expression, supporting its role as a negative regulator. Interestingly, loss of plfB significantly increased bacterial colonization in the lung of 6-day-old turkey poults. Further, complementation of plfB restored plf fimbrial expression and colonization of turkey lungs to wild-type levels. This further supports an important role for PL fimbriae for colonization of turkey lungs, since loss of plfB which resulted in increased plf gene expression in turkey lungs also correlated with higher bacterial numbers in the lungs. Taken together, these results indicate that PlfB acts as a negative regulator to reduce levels of PL fimbrial expression, under some conditions, but that it is not required for plf expression. This contrasts with the role the PapB regulator, which has been shown to play an essential role in expression of P fimbriae in uropathogenic E. coli strains. IMPORTANCE Regulation of E. coli PL fimbriae, encoded by plf , remains poorly understood. We investigated the role of a novel PapB-family transcriptional regulator, PlfB. In a plfB mutant plf transcription and fimbrial production were increased. In gel shift assays PlfB bound to the plfA promoter region. A P plfA – lux reporter further demonstrated increased and sustained expression in the plfB mutant. Deletion of genes encoding global regulators supported positive roles for Lrp and ArgR and a negative role for H-NS in plf regulation. Importantly, deletion of plfB significantly increased colonization of turkey lungs. These findings identify PlfB as a direct negative regulator of PL fimbriae and demonstrate that modulation of plf expression influences bacterial colonization during avian infection. Importantly, in contrast to most other PapB-family regulators, PlfB was shown to play a negative role in regulation of its cognate fimbrial system and was not required for optimal expression of fimbriae.

Source: bioRxiv (Cold Spring Harbor Laboratory)

DOI: 10.64898/2026.10.07.757495