Akrami, F. | Search bioRxiv

bioRxiv2026

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

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 PplfA-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.

microbiology↗

bioRxiv2026

Linear and Nonlinear Oscillatory Functional Brain Networks in Euthymic Bipolar Disorder Classification

Functional brain network (FBN) dysconnectivity has been repeatedly reported in bipolar disorder (BD). However, it remains unclear how this dysconnectivity manifests from the perspective of oscillatory FBNs, that is, which network measures and frequency bands most reliably capture this alteration. Moreover, it is unknown whether this dysconnection is predominantly expressed through linear or nonlinear interactions. Here, we investigated properties of oscillatory FBNs in individuals with euthymic BD. Networks were constructed using linear and nonlinear connectivity measures applied to source-localized resting-state electroencephalography (EEG) current density signals. We then quantified whole-FBN and nodal features using conventional and spectral graph theory methods to characterize disorder-related network mechanisms and evaluate their potential as biomarkers. Significant group differences between BD and control groups were observed in the theta and alpha1 bands. Dynamical whole-FBN alterations were detected primarily in linear oscillatory FBNs, with reduced Shannon entropy and energy in the BD group. These effects were replicated using machine learning, achieving 85% classification accuracy with entropy and energy as the most informative features. In contrast, nodal-level differences emerged mainly in nonlinear FBNs, revealing increased centrality in frontal, and decreased centrality across temporal, and limbic regions. These findings emphasize distinct, frequency-specific roles of linear and nonlinear oscillatory FBNs in BD, with global dysconnectivity reflected in linear FBNs and local alterations captured by nonlinear connectivity. Moreover, network measures related to synchronization stability and complexity more effectively capture BD-related dysconnectivity, suggesting that dynamic features of oscillatory FBNs may serve as potential biomarkers for BD.

neuroscience↗