Suchergebnisse

Bacterial conjugation is the process by which a conjugative element (CE) is transferred horizontally from a donor to a recipient cell via a connecting pore. One of the first steps in the conjugation process is the formation of a nucleoprotein complex at the origin of transfer (oriT), where one of the components of the nucleoprotein complex, the relaxase, introduces a site- and strand specific nick to initiate the transfer of a single DNA strand into the recipient cell. In most cases, the nucleoprotein complex involves, besides the relaxase, one or more additional proteins, named auxiliary proteins, which are encoded by the CE and/or the host. The conjugative plasmid pLS20 replicates in the Gram-positive Firmicute bacterium Bacillus subtilis. We have recently identified the relaxase gene and the oriT of pLS20, which are separated by a region of almost 1 kb. Here we show that this region contains two auxiliary genes that we name aux1LS20 and aux2LS20, and which we show are essential for conjugation. Both Aux1LS20 and Aux2LS20 are predicted to contain a Ribbon-Helix-Helix DNA binding motif near their N-terminus. Analyses of the purified proteins show that Aux1LS20 and Aux2LS20 form tetramers and hexamers in solution, respectively, and that they both bind preferentially to oriTLS20, although with different characteristics and specificities. In silico analyses revealed that genes encoding homologs of Aux1LS20 and/or Aux2LS20 are located upstream of almost 400 relaxase genes of the RelLS20 family (MOBL) of relaxases. Thus, Aux1LS20 and Aux2LS20 of pLS20 constitute the founding member of the first two families of auxiliary proteins described for CEs of Gram-positive origin. ; Ministry of Economy and Competitiveness of the Spanish Government to WM, which also funded AM-A, CG-C, and JV-C. Part of the economic support of the two aforementioned grants was provided by the "Agencia Estatal de Investigación (AEI)" and "Fondo Europeo de Desarrollo Regional (FEDER)." This research was also supported by institutional grants from the "Fundación Ramón Areces" and "Banco de Santander" to the Centro de Biología Molecular "Severo Ochoa

23 p.-5 fig.-2 tab. ; Antibiotic resistance is a serious global problem. Antibiotic resistance genes (ARG), which are widespread in environmental bacteria, can be transferred to pathogenic bacteria via horizontal gene transfer (HGT). Gut microbiomes are especially apt for the emergence and dissemination of ARG. Conjugation is the HGT route that is predominantly responsible for the spread of ARG. Little is known about conjugative elements of Gram-positive bacteria, including those of the phylum Firmicutes, which are abundantly present in gut microbiomes. A critical step in the conjugation process is the relaxase-mediated site-and strand-specific nick in the oriT region of the conjugative element. This generates a single-stranded DNA molecule that is transferred from the donor to the recipient cell via a connecting channel. Here we identified and characterized the relaxosome components oriT and the relaxase of the conjugative plasmid pLS20 of the Firmicute Bacillus subtilis. We show that the relaxase gene, named rel(LS20), is essential for conjugation, that it can function in trans and provide evidence that Tyr26 constitutes the active site residue. In vivo and in vitro analyses revealed that the oriT is located far upstream of the relaxase gene and that the nick site within oriT is located on the template strand of the conjugation genes. Surprisingly, the Rel(LS20) shows very limited similarity to known relaxases. However, more than 800 genes to which no function had been attributed so far are predicted to encode proteins showing significant similarity to RelLS20. Interestingly, these putative relaxases are encoded almost exclusively in Firmicutes bacteria. Thus, RelLS20 constitutes the prototype of a new family of relaxases. The identification of this novel relaxase family will have an important impact in different aspects of future research in the field of HGT in Gram-positive bacteria in general, and specifically in the phylum of Firmicutes, and in gut microbiome research. ; Work in the Meijer lab was funded by the Spanish government through grant Bio2013- 41489-P of the Ministry of Economy and Competitiveness, and through grant Bio2016- 77883-C2-1-P of the Ministry of Economy, Industry and Competitiveness; the former grant also funded AMA and CGC. The Spanish government also supported DRB, JRLO, and CA.DRB was funded by grant Bio2016-77883-C2-2-P of the Ministry of Economy, Industry and Competitiveness, and JRLO and CA were supported by grant BFU2014-52070-C2-2-P of the Ministry of Economy and Competitiveness to CA.LJW's work was supported by Wellcome Trust grant WT098374AIA to Jeff Errington. ; Peer reviewed

The principal route for dissemination of antibiotic resistance genes is conjugation by which a conjugative DNA element is transferred from a donor to a recipient cell. Conjugative elements contain genes that are important for their establishment in the new host, for instance by counteracting the host defense mechanisms acting against incoming foreign DNA. Little is known about these establishment genes and how they are regulated. Here, we deciphered the regulation mechanism of possible establishment genes of plasmid p576 from the Gram-positive bacterium Bacillus pumilus. Unlike the ssDNA promoters described for some conjugative plasmids, the four promoters of these p576 genes are repressed by a repressor protein, which we named Reg576. Reg576 also regulates its own expression. After transfer of the DNA, these genes are de-repressed for a period of time until sufficient Reg576 is synthesized to repress the promoters again. Complementary in vivo and in vitro analyses showed that different operator configurations in the promoter regions of these genes lead to different responses to Reg576. Each operator is bound with extreme cooperativity by two Reg576-dimers. The X-ray structure revealed that Reg576 has a Ribbon-Helix-Helix core and provided important insights into the high cooperativity of DNA recognition. ; Economy and Competitiveness of the Spanish Government [BFU2016-75471-C2-1-P (AEI/FEDER, EU) to C.A., BIO2013-41489-P (AEI/FEDER, EU) and BIO2016-77883-C2-1-P (AEI/FEDER, EU) to W.M., BIO2016-77883-C2-2-P (AEI/FEDER, EU) to R.B., BIO-2015-66203-P (AEI/FEDER, EU) to F.R., FIS2016-78313-P (AEI/FEDER, EU) to S.A.]; BIO2013-41489-P (AEI/FEDER, EU) and BIO2016-77883-C2-1-P (AEI/FEDER, EU) also supported J.V., A.M., and C.G.; Wellcome Investigator Award [209500 to Jeff Errington] supported L.W; 'Ramón y Cajal' Contract Supported S.A.; 'Agencia Estatal de Investigaci ´on' (AEI); 'Fondo Europeo de Desarrollo Regional (FEDER); European Union (EU)