The YfgL lipoprotein is required for cell adhesion and invasion, type I fimbriae expression and virulence of Klebsiella pneomoniae infecion

To address and clarify the regulatory function of YfgL in K. pneumoniae, the transcriptome analyses of the yfgL mutant and the wild-type strain were compared. K. pneumoniae strain deleted for yfgL exhibited reduced adherence and invasion to host cells. A previous study has demonstrated that the YfgL lipoprotein is essential for type III secretion system expression of Salmonella enterica serovar Enteritidis. Several putative secretion systems, but not type III secretion system, were already identified of the genome of the NTUH-K2044. Transcription of type 1 fimbriae was more highly induced in the wild-type than in the yfgL mutant strain. In addition to the fim gene cluster, genes encoding some amino acid metabolism, peptidoglycan synthesis and putative phosphoenopyruvate:carbohydrate phosphotransferase system (PTS), including the tdc gene cluster, yraM and the kp0760-kp0763 (pts) gene cluster, were also up-regulated by YfgL. Among a total 2,848 cloned sequences covering 99.9% of the entire genome sequence of NTUH-K2044, the expression of 9 cloned sequences was up-regulated and 3 cloned sequences were down-regulated at a cut-off value of 2. Total RNA was purified with the RNeasy Mini Kit (Qiagen) from log-phase cultures of the NTUH-K2044 wild-type and yfgL mutant K. pneumoniae strains in LB medium. Total RNA (40 μg) labeling, microarray hybridization, colorimetric detection and densitometry were performed and analyzed. Expression level of 23S rRNA on each membrane was used as an internal standard for normalization.