Gene transfer agent

Gene transfer agents (GTAs) are DNA-containing virus-like particles that are produced by some bacteria and archaea and mediate horizontal gene transfer. GTAs package random segments of DNA present in the host bacterium. After they are released by breaking open the host cell, they can inject their DNA into other cells, where it can become part of the recipient cells' chromosomes. GTAs appear to have originated from different viruses in several bacterial and archaeal lineages, such as Alphaproteobacteria, Spirochaetes and methanogenic archaea.[1][2][3]

Origin of gene transfer agents

GTA gene clusters are derived from bacteriophage DNA that has integrated into the host chromosome. Such prophages often acquire mutations that make them unable to produce phage particles, and many bacterial genomes contain one or more such defective prophages that have undergone more-or-less extensive mutation and deletion. In contrast, gene transfer agents arise when a prophage retains functional structural genes but undergoes mutations that remove the genes specifying its regulation and DNA replication, placing the structural genes under the control of cellular regulatory systems.

The Rhodobacter capsulatus GTA

The GTA produced by the alphaproteobacterium Rhodobacter capsulatus, named R. capsulatus GTA (RcGTA), is currently the best studied GTA. When cultured in laboratory conditions, a subset of the bacterial population induces production of RcGTA upon entry into stationary phase, which are subsequently released from the cells through cell lysis.[4] Most of the RcGTA structural genes are encoded in a ~ 15 kb genetic cluster on the bacterial chromosome. However, other genes required for RcGTA function, such as the genes required for RcGTA release through cell lysis are located separately.[1][5] Production of RcGTA appears to be controlled by the host cell, because several host systems, including a quorum sensing system and a histidine kinase and response regulator [1] are required for RcGTA transduction. Furthermore, the ability of cells to receive genetic material transduced by RcGTA requires a capsular polysaccharide receptor, which is regulated by the quorum sensing system.[6]

RcGTA-like clusters are found in several alphaproteobacteria.[7] Recently, several members of the order Rhodobacterales have been demonstrated to produce functional RcGTA-like particles.[8][9] Moreover, groups of genes with homology to the RcGTA are present in the chromosomes of various types of alphaproteobacteria.[10]

The Bartonella GTA

Another known case of a GTA present in alphaproteobacteria is the Bartonella GTA (BaGTA). The Bartonellaceae do not contain RcGTA homologs, but many of the species within this family contain the BaGTA, a GTA that originated from a different bacteriophage. The BaGTA acts jointly with another group of genes of bacteriophage origin, which cause run-off replication, a phenomenon by which replication starts at a prophage replication origin but does not stop at the usual prophage boundaries.[11] The run-off replication causes the amplification of a chromosome region containing genes such as secretion systems or adhesins.[11][12] As a consequence, the higher copy number of this region increases the probability that genes encoding host-association factors will be horizontally transferred. This property distinguishes the mechanisms of the BaGTA and the RcGTA, which have been named to be specialist or generalist GTA systems, respectively. The evolutionary patterns caused by the facilitated horizontal transfer caused by the Bartonella specialist GTA have been suggested to have caused the Bartonella radiation, in which these bacteria adapted to commensal or pathogenic lifestyles in various groups of mammalian hosts.[12]

See also

References

  1. 1 2 3 Lang, A. S.; Zhaxybayeva, O.; Beatty, J. T. (2012). "Gene transfer agents: Phage-like elements of genetic exchange". Nature Reviews Microbiology. 10: 472–82. doi:10.1038/nrmicro2802. PMC 3626599. PMID 22683880.
  2. ↑ Stanton TB (2007). "Prophage-like gene transfer agents-novel mechanisms of gene exchange for Methanococcus, Desulfovibrio, Brachyspira, and Rhodobacter species". Anaerobe. 13 (2): 43–9. doi:10.1016/j.anaerobe.2007.03.004. PMID 17513139.
  3. ↑ Wagner A, Whitaker RJ, Krause DJ, Heilers JH, van Wolferen M, van der Does C, Albers SV (2017). "Mechanisms of gene flow in archaea". Nat. Rev. Microbiol. 15 (8): 492–501. doi:10.1038/nrmicro.2017.41. PMID 28502981.
  4. ↑ Fogg, P. C. M.; Westbye, A. B.; Beatty, J. T. (2012). Banfield, Bruce W, ed. "One for All or All for One: Heterogeneous Expression and Host Cell Lysis Are Key to Gene Transfer Agent Activity in Rhodobacter capsulatus". PLoS ONE. 7 (8): e43772. Bibcode:2012PLoSO...743772F. doi:10.1371/journal.pone.0043772. PMC 3423380. PMID 22916305.
  5. ↑ Westbye, A. B.; Leung, M. M.; Florizone, S.; Taylor, T. A.; Johnson, J. A.; Fogg, P. C.; Beatty, J. T. (2013). "Phosphate concentration and the putative sensor-kinase protein CckA modulate cell lysis and release of the Rhodobacter capsulatus gene transfer agent (RcGTA)". Journal of Bacteriology. 195: 5025–40. doi:10.1128/JB.00669-13. PMC 3811591. PMID 23995641.
  6. ↑ Brimacombe, C. A.; Stevens, A.; Jun, D.; Mercer, R.; Lang, A. S.; Beatty, J. T. (2013). "Quorum-sensing regulation of a capsular polysaccharide receptor for the Rhodobacter capsulatus gene transfer agent (RcGTA)". Molecular Microbiology. 87 (4): 802–817. doi:10.1111/mmi.12132. PMC 3641046. PMID 23279213.
  7. ↑ Lang, AS and Beatty, JT (2007) "Importance of widespread gene transfer agent genes in alpha-proteobacteria." Trends in Microbiology, 15(2) pp. 54–62. (Review)
  8. ↑ McDaniel, L. D.; Young, E.; Delaney, J.; Ruhnau, F.; Ritchie, K. B.; Paul, J. H. (2010). "High Frequency of Horizontal Gene Transfer in the Oceans". Science. 330 (6000): 50. Bibcode:2010Sci...330...50M. doi:10.1126/science.1192243. PMID 20929803.
  9. ↑ Maxmen, A. (2010). "Virus-like particles speed bacterial evolution". Nature. doi:10.1038/news.2010.507.
  10. ↑ Lang AS, Beatty JT (2007). "Importance of widespread gene transfer agent genes in alpha-proteobacteria". Trends Microbiol. 15 (2): 54–62. doi:10.1016/j.tim.2006.12.001. PMID 17184993.
  11. 1 2 Berglund EC, Frank AC, Calteau A, Vinnere Pettersson O, Granberg F, Eriksson AS, Näslund K, Holmberg M, Lindroos H, Andersson SG (2009). "Run-off replication of host-adaptability genes is associated with gene transfer agents in the genome of mouse-infecting Bartonella grahamii". PLoS Genet. 5 (7): e1000546. doi:10.1371/journal.pgen.1000546. PMC 2697382. PMID 19578403.
  12. 1 2 Guy L, Nystedt B, Toft C, Zaremba-Niedzwiedzka K, Berglund EC, Granberg F, Näslund K, Eriksson AS, Andersson SG (2013). "A gene transfer agent and a dynamic repertoire of secretion systems hold the keys to the explosive radiation of the emerging pathogen Bartonella". PLoS Genet. 9 (3): e1003393. doi:10.1371/journal.pgen.1003393. PMC 3610622. PMID 23555299.
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