Abstract
Bacteria can modify their morphology in response to environmental stimuli for survival or host defense evasion. The rich glucose in vivo or in the Luria–Bertani (LB) medium shortened the cell length of Klebsiella pneumoniae. The environmental glucose decreased the levels of cyclic AMP (cAMP) and the transcription of crp, which declined the cAMP–cAMP receptor protein (cAMP-CRP) activity. The cell length of crp deletion mutant was significantly shorter than that of the wild type (0.981 ± 0.057 μm vs. 2.415 ± 0.075 μm, P < 0.001). These results indicated that the high environmental glucose alters the bacterial morphology to a round form through regulating the activity of cAMP-CRP complex. Comparative proteomics analysis showed increased expression of 10 proteins involved in cell division or cell wall biosynthesis in the crp deletion strain. Five of them (ompA, tolB, ybgC, ftsI, and rcsF) were selected to verify their expression in the high-glucose environment, and overexpression of tolB or rcsF shortened the bacterial length similar to that of the crp deletion strain. Electrophoretic mobility shift assay indicated that CRP directly negatively regulates the transcription of tolB and rcsF by binding to the promoter regions. This study first proved the role and partial regulation mechanism of CRP in altering cell morphology during infection and provided a theoretical basis for elucidating the mechanism in diabetes mellitus susceptible to K. pneumoniae.
Highlights
Klebsiella pneumoniae is a rod-shaped, Gram-negative bacterium that belongs to the family Enterobacteriaceae and is widely distributed in the mouth, skin, intestines, hospital settings, and medical devices
The CRP binding sites on the promoter regions of tolB and rcsF genes were found and cyclic AMP (cAMP)-CRP complex could directly regulate the proteins expression. These results indicated that the cAMP-CRP pathway is a key regulatory pathway that regulates cell shape to correspond to the environmental glucose changes, and tolB and rcsF play roles in this processing through direct regulation by cAMP-CRP complex
This phenomenon suggests that a high-glucose environment enhances the pathogenicity of bacteria, which may contribute to the high susceptibility to K. pneumoniae infection in DM
Summary
Klebsiella pneumoniae is a rod-shaped, Gram-negative bacterium that belongs to the family Enterobacteriaceae and is widely distributed in the mouth, skin, intestines, hospital settings, and medical devices. This bacterium is an opportunistic pathogen responsible for many nosocomial infections ranging from urinary tract infection to pneumonia. Exogenous glucose could stimulate the production of CPS and type 3 fimbriae, the virulence factors of K. pneumoniae (Lin et al, 2013b, 2016). These processes are regulated by the global regulator cyclic AMP (cAMP) receptor protein (CRP) and cAMP-CRP signaling pathway. The supply of environmental glucose can inhibit the production of the intracellular second messenger cAMP and inactivate the cAMP-CRP signaling pathway (Lin et al, 2013b, 2016)
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