Abstract
The Hfq protein is a bacterial RNA chaperone, involved in many molecular interactions, including control of actions of various small RNA regulatory molecules. We found that the presence of Hfq was required for survival of plasmid-containing Escherichia coli cells against high concentrations of chloramphenicol (plasmid p27cmr), tetracycline (pSC101, pBR322) and ampicillin (pBR322), as hfq+ strains were more resistant to these antibiotics than the hfq-null mutant. In striking contrast, production of Hfq resulted in low resistance to high concentrations of kanamycin when the antibiotic-resistance marker was chromosome-borne, with deletion of hfq resulting in increasing bacterial survival. These results were observed both in solid and liquid medium, suggesting that antibiotic resistance is an intrinsic feature of these strains rather than a consequence of adaptation. Despite its major role as RNA chaperone, which also affects mRNA stability, Hfq was not found to significantly affect kan and tet mRNAs turnover. Nevertheless, kan mRNA steady-state levels were higher in the hfq-null mutant compared to the hfq+ strain, suggesting that Hfq can act as a repressor of kan expression.This observation does correlate with the enhanced resistance to high levels of kanamycin observed in the hfq-null mutant. Furthermore, dependency on Hfq for resistance to high doses of tetracycline was found to depend on plasmid copy number, which was only observed when the resistance marker was expressed from a low copy plasmid (pSC101) but not from a medium copy plasmid (pBR322). This suggests that Hfq may influence survival against high doses of antibiotics through mechanisms that remain to be determined. Studies with pBR322Δrom may also suggest an interplay between Hfq and Rom in the regulation of ColE1-like plasmid replication. Results of experiments with a mutant devoid of the part of the hfq gene coding for the C-terminal region of Hfq suggested that this region, as well as the N-terminal region, may be involved in the regulation of expression of antibiotic resistance in E. coli independently.
Highlights
The Hfq protein has been discovered in studies on Escherichia coli bacteriophage Qβ as a factor required for RNA replication of this virus [1]
Δhfq::kan mutation, and ΔCTRhfq::kan
The Hfq protein has been indicated as a factor involved in development of bacterial virulence and modulation of microbial response to antibiotics [16,17,18,19,20,21,22,23,24,25,26,27], and this protein has been proposed as a novel target for antibacterial drugs [30], the question about its functions in expressing resistance to high concentrations of antibiotics has not been addressed previously
Summary
The Hfq protein has been discovered in studies on Escherichia coli bacteriophage Qβ as a factor required for RNA replication of this virus [1]. Subsequent studies indicated that this small protein, encoded by the hfq gene, interacts with various RNA species, acting as an RNA chaperone. This activity results in regulation of expression of many genes, especially at the stage of post-transcriptional modulations of RNA-RNA interactions and controlling availability of mRNA molecules to the translation process (reviewed in [2,3,4]). The E. coli Hfq protein is composed of 102 amin acid (aa) residues and consists of two structural regions, called the N-terminal region (NTR) and the C-terminal region (CTR) (Figure 1). NTR (about 65 aa residues, though sometimes it is suggested to cover 72 aa) contains the capping α-helical structure and five β-stands, and it is responsible
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