Abstract
Most Acinetobacter baumannii strains are naturally competent. Although some information is available about factors that enhance or reduce the frequency of the transformation of this bacterium, the regulatory elements and mechanisms are barely understood. In this article, we describe studies on the role of the histone-like nucleoid structuring protein, H-NS, in the regulation of the expression of genes related to natural competency and the ability to uptake foreign DNA. The expression levels of the natural transformation-related genes pilA, pilT, pilQ, comEA, comEC, comF, and drpA significantly increased in a Δhns derivative of A. baumannii A118. The complementation of the mutant with a recombinant plasmid harboring hns restored the expression levels of six of these genes (pilT remained expressed at high levels) to those of the wild-type strain. The transformation frequency of the A. baumannii A118 Δhns strain was significantly higher than that of the wild-type. Similar, albeit not identical, there were consequences when hns was deleted from the hypervirulent A. baumannii AB5075 strain. In the AB5075 complemented strain, the reduction in gene expression in a few cases was not so pronounced that it reached wild-type levels, and the expression of comEA was enhanced further. In conclusion, the expression of all seven transformation-related genes was enhanced after deleting hns in A. baumannii A118 and AB5075, and these modifications were accompanied by an increase in the cells’ transformability. The results highlight a role of H-NS in A. baumannii’s natural competence.
Highlights
The histone-like nucleoid structuring protein (H-NS) is a global regulator, widely distributed among different genera of bacteria
Quantitative RT-PCR assays using total RNA demonstrated that the expression levels of all tested genes were significantly increased (Figure 1A)
The global repressor H-NS modulates the expression of a plethora of A. baumannii genes with functions related to virulence, biosynthetic pathways, cell adhesion, quorum sensing, and autotransporters, among others
Summary
The histone-like nucleoid structuring protein (H-NS) is a global regulator, widely distributed among different genera of bacteria. H-NS-like proteins are shown to assist horizontal DNA transmission and have important implications for bacterial evolution [1]. In Enterobacteriaceae, H-NS acts as a transcriptional repressor of the type I-E CRISPR-Cas system leading to natural transformation events [2,3]. A correlation between H-NS-mediated regulation and the lack of conservation of the respective potential horizontally acquired gene clusters in different Acinetobacter sp. This evidence indicated that H-NS acts as a xenogenic repressor in A. baumannii [4]. One of the main HGT mechanisms that promotes the integration of exogenous DNA, has been documented in approximately 80 bacterial species [5,7]. A. baumannii’s genomes are highly variable, showing large segments of DNA of different origins, which often code for virulence factors, adaptability systems, and antibiotic resistance [21–24]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
