Transcriptional antitermination integrates the expression of loci of diverse phage origin in the chimeric Bartonella Gene Transfer Agent BaGTA
Curation statements for this article:-
Curated by eLife
eLife Assessment
This manuscript describes an important finding of the transcriptional control of a chimeric gene transfer agents (GTA) cluster in Bartonella by a processive anti-termination factor (BrrG). The evidence provided is solid. This manuscript will interest researchers working on transcriptional regulation, horizontal gene transfer, and phages.
This article has been Reviewed by the following groups
Listed in
- Evaluated articles (eLife)
Abstract
Gene Transfer Agents (GTAs) are mobile genetic elements derived from bacteriophages that mediate genome-wide horizontal gene transfer (HGT) in diverse groups of prokaryotes. BaGTA, encoded by all the pathogens of the genus Bartonella , is a chimeric GTA that evolved by the domestication of two phages. The run-off-replication module ROR of one phage is integrated with the capsid production, DNA packaging and lysis machinery Bgt of a second phage. Restricted to a self-sacrifying subset of the bacterial population, the position-specific DNA amplification and packaging of a genomic plasticity region enriched for genes involved in host interaction and adaptation selectively enhances the HGT frequency of these pathogenicity genes. This feature of BaGTA is considered a key innovation underlying the evolutionary success of Bartonella . Little is known, however, about the mechanism mediating the coordinated expression of the ror and bgt loci. Here, we established the regulatory hierarchy, with ror acting upstream of the capsid gene cluster bgtA-K . BrrG, encoded by the ror locus, controls the transcription of the bgtA-K operon by functioning as a processive antiterminator. This study provides the first insights into the mechanism controlling the coordinated expression of the two BaGTA modules of divergent phage origin. Beyond BaGTA, we propose that antitermination is a broadly relevant mechanism for controlling HGT by GTAs of the Alphaproteobacteria.
Article activity feed
-
eLife Assessment
This manuscript describes an important finding of the transcriptional control of a chimeric gene transfer agents (GTA) cluster in Bartonella by a processive anti-termination factor (BrrG). The evidence provided is solid. This manuscript will interest researchers working on transcriptional regulation, horizontal gene transfer, and phages.
-
Reviewer #1 (Public review):
Summary:
Gene transfer agent (GTA) from Bartonella is a fascinating chimeric GTA that evolved from the domestication of two phages. Not much is known about how the expression of the BaGTA is regulated. In this manuscript, Korotaev et al noted the structural similarity between BrrG (a protein encoded by the ror locus of BaGTA) to a well-known transcriptional anti-termination factor, 21Q, from phage P21. This sparked the investigation into the possibility that BaGTA cluster is also regulated by anti-termination. Using a suite of cell biology, genetics, and genome-wide techniques (ChIP-seq), Korotaev et al convincingly showed that this is most likely the case. The findings offer the first insight into the regulation of GTA cluster (and GTA-mediated gene transfer) particularly in this pathogen Bartonella. Note …
Reviewer #1 (Public review):
Summary:
Gene transfer agent (GTA) from Bartonella is a fascinating chimeric GTA that evolved from the domestication of two phages. Not much is known about how the expression of the BaGTA is regulated. In this manuscript, Korotaev et al noted the structural similarity between BrrG (a protein encoded by the ror locus of BaGTA) to a well-known transcriptional anti-termination factor, 21Q, from phage P21. This sparked the investigation into the possibility that BaGTA cluster is also regulated by anti-termination. Using a suite of cell biology, genetics, and genome-wide techniques (ChIP-seq), Korotaev et al convincingly showed that this is most likely the case. The findings offer the first insight into the regulation of GTA cluster (and GTA-mediated gene transfer) particularly in this pathogen Bartonella. Note that anti-termination is a well-known/studied mechanism of transcriptional control. Anti-termination is a very common mechanism for gene expression control of prophages, phages, bacterial gene clusters, and other GTAs, so in this sense, the impact of the findings in this study here is limited to Bartonella.
Strengths:
Convincing results that overall support the main claim of the manuscript.
Weaknesses:
A few important controls are missing.
-
Reviewer #2 (Public review):
Summary:
In this study, the authors identified and characterized a regulatory mechanism based on transcriptional anti-termination that connects the two gene clusters, capsid and run-off replication (ROR) locus, of the bipartite Bartonella gene transfer agent (GTA). Among genes essential for GTA functionality identified in a previous transposon sequencing project, they found a potential antiterminatior of phage origin within the ROR locus. They employed fluorescence reporter and gene transfer assays of overexpression and knockout strains in combination with ChiPSeq and promoter-fusions to convincingly show that this protein indeed acts as an antiterminator counteracting attenuation of the capsid gene cluster expression.
Impact on the field:
The results provide valuable insights into the evolution of the …
Reviewer #2 (Public review):
Summary:
In this study, the authors identified and characterized a regulatory mechanism based on transcriptional anti-termination that connects the two gene clusters, capsid and run-off replication (ROR) locus, of the bipartite Bartonella gene transfer agent (GTA). Among genes essential for GTA functionality identified in a previous transposon sequencing project, they found a potential antiterminatior of phage origin within the ROR locus. They employed fluorescence reporter and gene transfer assays of overexpression and knockout strains in combination with ChiPSeq and promoter-fusions to convincingly show that this protein indeed acts as an antiterminator counteracting attenuation of the capsid gene cluster expression.
Impact on the field:
The results provide valuable insights into the evolution of the chimeric BaGTA, a unique example of phage co-domestication by bacteria. A similar system found in the other broadly studied Rhodobacterales/Caulobacterales GTA family suggests that antitermination could be a general mechanism for GTA control.
Strengths:
Results of the selected and carefully designed experiments support the main conclusions.
Weaknesses:
It remains open why overexpression of the antiterminator does not increase the gene transfer frequency.
-
