Research Article: RcsB regulation of the YfdX-mediated acid stress response in Klebsiella pneumoniae CG43S3

Date Published: February 28, 2019

Publisher: Public Library of Science

Author(s): Chia-Jui Liu, Ching-Ting Lin, Jo-Di Chiang, Chen-Yi Lin, Yen-Xi Tay, Li-Cheng Fan, Kuan-Nan Peng, Chih-Huan Lin, Hwei-Ling Peng, Horacio Bach.


In Klebsiella pneumoniae CG43S3, deletion of the response regulator gene rcsB reduced the capsular polysaccharide amount and survival on exposure to acid stress. A comparison of the pH 4.4-induced proteomes between CG43S3 and CG43S3ΔrcsB revealed numerous differentially expressed proteins and one of them, YfdX, which has recently been reported as a periplasmic protein, was absent in CG43S3ΔrcsB. Acid survival analysis was then conducted to determine its role in the acid stress response. Deletion of yfdX increased the sensitivity of K. pneumoniae CG43S3 to a pH of 2.5, and transforming the mutant with a plasmid carrying yfdX restored the acid resistance (AR) levels. In addition, the effect of yfdX deletion was cross-complemented by the expression of the periplasmic chaperone HdeA. Furthermore, the purified recombinant protein YfdX reduced the acid-induced protein aggregation, suggesting that YfdX as well as HdeA functions as a chaperone. The following promoter activity measurement revealed that rcsB deletion reduced the expression of yfdX after the bacteria were subjected to pH 4.4 adaptation. Western blot analysis also revealed that YfdX production was inhibited by rcsB deletion and only the plasmid expressing RcsB or the nonphosphorylated form of RcsB, RcsBD56A, could restore the YfdX production, and the RcsB-mediated complementation was no longer observed when the sensor kinase RcsD gene was deleted. In conclusion, this is the first study demonstrating that YfdX may be involved in the acid stress response as a periplasmic chaperone and that RcsB positively regulates the acid stress response partly through activation of yfdX expression. Moreover, the phosphorylation status of RcsB may affect the YfdX expression under acidic conditions.

Partial Text

The nosocomial pathogen Klebsiella pneumoniae causes suppurative lesions, septicemia, and infections of the urinary and respiratory tracts in immunocompromised patients [1, 2]. In Taiwan, the incidence of Klebsiella liver abscesses (KLAs) in patients with diabetes, malignancies, renal diseases, and pneumonia has steadily increased [3]. Recently, KLAs have also been reported in Western and other Asian countries [4]. Although several virulence traits, including K1 capsular polysaccharides [3], magA [5], iron acquisition loci on pLVPK [6], and type 1 and type 3 fimbriae [7, 8], have been implicated in the pathogenesis of KLAs, the pathogenic mechanism underlying KLAs remains unknown. The endogenous K. pneumoniae residing in a patient’s gastrointestinal (GI) tract has been reported to be the predisposing factor for KLA and several gastrointestinal diseases [9–11]. In addition, a recent report indicated that hospital-acquired K. pneumoniae infections are largely associated with the patients’ own GI microbiota [12]. Conceivably, determining the mechanism by which K. pneumoniae is retained in the GI tract is essential to elucidate the pathogenic mechanism. During GI colonization, exposure to acid pH in the stomach is a challenge that the bacteria must overcome. In K. pneumoniae, the tripartite efflux pump EffABC, lysine decarboxylase operon cadCBA and OxyR have been reported to regulate resistance to HCl [13–15].

A comparative analysis of the proteomes and the promoter activity analysis in K. pneumoniae CG43S3 demonstrated a positive control of YfdX expression by RcsB, which suggested that YfdX expression may be used as a reporter for the RcsB-mediated regulation of the acid response. The expression of yfdX is positively controlled by RcsB, and RcsD seems to be required to ensure that RcsB is in the nonphosphorylated form to activate the expression of YfdX. We have also demonstrated that YfdX as well as HdeA may function as periplasmic chaperones to protect K. pneumoniae CG43S3 from acid stress damage.




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