AUTHOR=Lin Tien-Huang , Chen Yeh , Kuo Jong-Tar , Lai Yi-Chyi , Wu Chien-Chen , Huang Chun-Fa , Lin Ching-Ting 

TITLE=Phosphorylated OmpR Is Required for Type 3 Fimbriae Expression in Klebsiella pneumoniae Under Hypertonic Conditions

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.02405

DOI=10.3389/fmicb.2018.02405

ISSN=1664-302X

ABSTRACT=<p>OmpR/EnvZ is a two-component system that senses osmotic signals and controls downstream gene expression in many species of <italic>Enterobacteriaceae</italic>. However, the role of OmpR/EnvZ in <italic>Klebsiella pneumoniae</italic> remains unknown. In this study, we found that production of MrkA, the major subunit of type 3 fimbriae, was decreased under hypertonic conditions. A deletion mutant of <italic>ompR</italic> and a site-directed mutant with a single amino acid substitution of aspartate 55 to alanine (D55A), which mimics the unphosphorylated form of OmpR, markedly reduced MrkA production under hypertonic conditions. These results indicate that <italic>K. pneumoniae</italic> type 3 fimbriae expression is activated by the phosphorylated form of OmpR (OmpR∼P). Although no typical OmpR∼P binding site was found in the P<italic><sub>mrkA</sub></italic> sequence, <italic>mrkA</italic> mRNA levels and P<italic><sub>mrkA</sub></italic> activity were decreased in the Δ<italic>ompR</italic> and <italic>ompR</italic><sub>D55A</sub> strains compared with the wild type (WT) strain, indicating that OmpR∼P mediates type 3 fimbriae expression at the transcriptional level. Previous reports have demonstrated that a cyclic-di-GMP (c-di-GMP) related gene cluster, <italic>mrkHIJ</italic>, regulates the expression of type 3 fimbriae. We found that both the <italic>ompR</italic> and <italic>ompR</italic><sub>D55A</sub> mutants exhibited decreased <italic>mrkHIJ</italic> mRNA levels, intracellular c-di-GMP concentration, and bacterial biofilm amount, but increased total intracellular phosphodiesterase activity in response to hypertonic conditions. These results indicate that OmpR∼P regulates type 3 fimbriae expression to influence <italic>K. pneumoniae</italic> biofilm formation via MrkHIJ and modulation of intracellular c-di-GMP levels. Taken together, we herein provide evidence that OmpR∼P acts as a critical factor in the regulation of the c-di-GMP signaling pathway, type 3 fimbriae expression, and biofilm amount in <italic>K. pneumoniae</italic> in response to osmotic stresses.</p>