Identification of a two-component regulatory system involved in antimicrobial peptide resistance in Streptococcus pneumoniae.

Two-component regulatory systems (TCS) are among the most widespread mechanisms that bacteria use to sense and respond to environmental changes. In the human pathogen Streptococcus pneumoniae, a total of 13 TCS have been identified and many of them have been linked to pathogenicity. Notably, TCS01 strongly contributes to pneumococcal virulence in several infection models. However, it remains one of the least studied TCS in pneumococci and its functional role is still unclear. In this study, we demonstrate that TCS01 cooperates with a BceAB-type ABC transporter to sense and induce resistance to structurally-unrelated antimicrobial peptides of bacterial origin that all target undecaprenyl-pyrophosphate or lipid II, which are essential precursors of cell wall biosynthesis. Even though tcs01 and bceAB genes do not locate in the same gene cluster, disruption of either of them equally sensitized the bacterium to the same set of antimicrobial peptides. We show that the key function of TCS01 is to upregulate the expression of the transporter, while the latter appears the main actor in resistance. Electrophoretic mobility shift assays further demonstrated that the response regulator of TCS01 binds to the promoter region of the bceAB genes, implying a direct control of these genes. The BceAB transporter was overexpressed and purified from E. coli. After reconstitution in liposomes, it displayed substantial ATPase and GTPase activities that were stimulated by antimicrobial peptides to which it confers resistance to, revealing new functional features of a BceAB-type transporter. Altogether, this inducible defense mechanism likely contributes to the survival of the opportunistic microorganism in the human host, in which competition among commensal microorganisms is a key determinant for effective host colonization and invasive path.

Ebola Virus GP Gene Polyadenylation Versus RNA Editing.

Synthesis of Ebola virus (EBOV) surface glycoprotein (GP) is dependent on transcriptional RNA editing. Northern blot analysis of EBOV-infected cells using GP-gene-specific probes reveals that, in addition to full-length GP messenger RNAs (mRNAs), a shorter RNA is also synthesized, representing >40% of the total amount of GP mRNA. Sequence analysis demonstrates that this RNA is a truncated version of the full-length GP mRNA that is polyadenylated at the editing site and thus lacks a stop codon. An absence of detectable levels of protein synthesis in cellulo is consistent with the existence of tight regulation of the translation of such mRNA. However, nonstop GP mRNA was shown to be only slightly less stable than the same mRNA containing a stop codon, against the general belief in nonstop decay mechanisms aimed at detecting and destroying mRNAs lacking a stop codon. In conclusion, we demonstrate that the editing site indeed serves as a cryptic transcription termination/polyadenylation site, which rarely also functions to edit GP mRNA for expression of surface GP. This new data suggest that the downregulation of surface GP expression is even more dramatic than previously thought, reinforcing the importance of the GP gene editing site for EBOV replication and pathogenicity.