Horizontal gene transfer in Thermus thermophilus: mechanisms and barriers
Author
Blesa Esteban, AlbaAdvisor
Berenguer Carlos, JoséEntity
UAM. Departamento de Biología MolecularDate
2016-02-12Subjects
Bacterias termofílicas - Tesis doctorales; Biología y Biomedicina / BiologíaNote
Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología Molecular. Fecha de lectura: 12-02-2016Esta tesis tiene embargado el acceso al texto completo hasta el 12-08-2019
La autora no permite ningún tipo de modificación en el excel
Esta obra está bajo una licencia de Creative Commons Reconocimiento-NoComercial-SinObraDerivada 4.0 Internacional.
Abstract
Comparative genome analysis have evidenced that fluent genetic exchange is
mainly mediated by Horizontal Gene Transfer (HGT), thus recognized as a leading
force of prokaryotic evolution and microbial genetic diversity. Transduction,
transformation and conjugation are the three standard mechanisms driving HGT.
The ancient thermophilic bacteria Thermus thermophilus laterally transfers DNA
in a really efficient way due to a highly sophisticated competence machinery as well as
by a conjugation-like process. However, conjugation in T. thermophilus emerges rather
unconventional as it is efficient between isogenic cells, thus, bidirectional, and no type
IV secretion systems seems to be involved. Besides, genes associated to the
megaplasmid are transferred with higher frequencies (~10 fold) than those localized in
the chromosome. No evident order in the transfer among megaplasmid markers
contrasts with the identification of multiple hotspots of transfer in the chromosome.
Several of these loci showing higher transfer frequencies are encoded near putative
Tth111 type II restriction sites which might work as OriTs. The competence machinery
actively participates in conjugation, being required in the receptor cell but not in the
donor. Hence, a two-step model (push-pull) is proposed, where the donor energetically
pumps DNA to a receptor cell, which actively pulls in the DNA transferred with its
competence apparatus. Two active hexameric ATPases, named CptA and HerA,
paralogs to the helicases HerA and Ftsk from other bacteria, have been identified as
chief components of the pushing step. Therefore, T. thermophilus is able to proficiently
exchange DNA by transformation (including DNA-protected vesicles which could work
as long distance vehicles), and largely by conjugation. This fruitful dynamic gene flow
is compatible with a battery of protective strategies to prevent potentially harmful
invasion of genetic parasites. Among them, the Argonaute protein elicits a DNA-DNA
interference on DNA taken up by transformation. We proved larger insights of
Argonaute-mediated interference, acting, in vivo, against virtually any kind of DNA
template. However, when such DNA is transferred by a conjugation-like process,
Argonaute is not activated, suggesting a selective immunity towards the way in which
DNA is acquired. This fact, together with the higher efficiency shown by conjugation
compared to natural competence when the same DNA was transferred, enforcedthe
proposal of conjugation as the major motor of shared traits among populations of
Thermus spp in thermal environments. Finally, we analyse the role of the PrimPol
polymerase as a ssDNA guide supplier for the Argonaute protein.
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Texto de la Tesis Doctoral
Google Scholar:Blesa Esteban, Alba
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