Carboxy-Terminal Processing Protease Controls Production of Outer Membrane Vesicles and Biofilm in Acinetobacter baumannii.

Rakesh Roy,Nien-Tsung Lin,Chiou-Ying Yang,Ren-In You,Chan-Hua Chang

doi:10.3390/microorganisms9061336

Rakesh Roy, Nien-Tsung Lin + Show 3 more

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https://doi.org/10.3390/microorganisms9061336

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Abstract

Carboxy-terminal processing protease (Ctp) is a serine protease that controls multiple cellular processes through posttranslational modification of proteins. Acinetobacter baumannii ATCC 17978 ctp mutant, namely MR14, is known to cause cell wall defects and autolysis. The objective of this study was to investigate the role of ctp mutation–driven autolysis in regulating biofilms in A. baumannii and to evaluate the vesiculation caused by cell wall defects. We found that in A. baumannii, Ctp is localized in the cytoplasmic membrane, and loss of Ctp function enhances the biofilm-forming ability of A. baumannii. Quantification of the matrix components revealed that extracellular DNA (eDNA) and proteins were the chief constituents of MR14 biofilm, and the transmission electron microscopy further indicated the presence of numerous dead cells compared with ATCC 17978. The large number of MR14 dead cells is potentially the result of compromised outer membrane integrity, as demonstrated by its high sensitivity to sodium dodecyl sulfate (SDS) and ethylenediaminetetraacetic acid (EDTA). MR14 also exhibited the hypervesiculation phenotype, producing outer-membrane vesicles (OMVs) of large mean size. The MR14 OMVs were more cytotoxic toward A549 cells than ATCC 17978 OMVs. Our overall results indicate that A. baumannii ctp negatively controls pathogenic traits through autolysis and OMV biogenesis.

Highlights

Acinetobacter baumannii, an opportunistic, nosocomial pathogen, is associated with an outbreak of various human infections related to wound, burn, bloodstream, urinary tract and pneumonia, leading to increasing mortality [1]
While in our previous paper we demonstrated ctp gene in A. baumannii to have role in motility, membrane integrity, autolysis and virulence [33], in our current paper we studied about the consequences of ctp gene mutation in terms of biofilm and outer-membrane vesicles (OMVs) biogenesis that may be the indirect effect of enhanced membrane defects and elevated cell envelope stress responses caused by the loss of Carboxy-terminal processing protease (Ctp)
The study findings elucidate the consequences of ctp gene mutation in term of OMV biogenesis and biofilm formation in A. baumannii

Summary

Introduction

Acinetobacter baumannii, an opportunistic, nosocomial pathogen, is associated with an outbreak of various human infections related to wound, burn, bloodstream, urinary tract and pneumonia, leading to increasing mortality [1]. Due to an increase in the prevalence of multidrug-resistant A. baumannii, it is considered a priority pathogen in the research and development of novel antimicrobials. The bacterial cell wall as a therapeutic target has been a topic of research for decades because of its essentiality [2]. Mechanistic studies targeting the cell wall of A. baumannii are limited. The major component of the cell wall is peptidoglycan (PG). PBPs play an essential role in cell wall elongation, shape determination, septation and PG cross-linking [4]. A study demonstrated that PBP3 and PBP7 are processed by Prc protease in Escherichia coli [5].

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