The pLS20 family of plasmids and regulation of their establishment genes
Título (trad.)
La familia de plásmidos pLS20 y la regulación de sus genes de establecimientoAutor (es)
Val Calvo, JorgeDirector (es)
Meijer, Wiflfried J.J.Entidad
UAM. Departamento de Biología Molecular; Centro de Biología Molecular Severo Ochoa (CBM)Fecha de edición
2021-02-25Materias
Plásmidos; Biología y Biomedicina / BiologíaNota
Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología Molecular. Fecha de lectura: 25-02-2021Esta tesis tiene embargado el acceso al texto completo hasta el 25-08-2022
Esta obra está bajo una licencia de Creative Commons Reconocimiento-NoComercial-SinObraDerivada 4.0 Internacional.
Resumen
The spread of antibiotic resistance genes (ARGs) is a major threat to global health. Horizontal gene
transfer (HGT) events, and particularly the route of bacterial conjugation, are mainly responsible for
the dissemination of ARGs. Conjugation is the process by which a conjugative element is transferred
from a donor to a recipient cell through a connecting channel. Conjugative elements are often located on
plasmids. Conjugative plasmids are widespread in Gram-positive (Gram+) and Gram-negative (Gram�)
bacteria. Most conjugation studies are based on conjugative plasmids from Gram� bacteria though. In
our laboratory, we study as a model the conjugative plasmid pLS20 from the Gram+ bacterium Bacillus
subtilis. One main objective of this work was to determine the rareness of pLS20; is it a unique plasmid
or does it belong to a family of related plasmids. Results obtained in these thesis studies show that pLS20
is the prototype of a new family of conjugative plasmids that is present in several Bacillus species isolated
from diverse geographic locations and niches, suggesting that their distribution is worldwide. The
pLS20 family of plasmids is characterised by an unusual (i) origin of replication region, that does not
encode for a typical replication initiation protein, which is flanked on its left side by (ii) a partitioning
system, and on its right side by (iii) a large conjugation operon. Interestingly, the conjugation module of
pLS20 is also (partially) present on other Bacillus plasmids as well as on plasmids from other Gram+
bacteria including pathogens such as Listeria, Enterococcus and Clostridium species, indicating that this
conjugation module is widely distributed among conjugative plasmids hosted by bacteria of the phylum
Firmicutes.
Bacteria contain systems to defend themselves against incoming foreign DNA. Establishment of a plasmid
in the recipient host after conjugative transfer requires a transient inactivation of these host-defence
mechanisms. Many conjugative plasmids contain so-called establishment genes that fulfil this role. In
this doctoral thesis, I identified the putative establishment genes present on members of the pLS20 family
of plasmids. The establishment genes on these plasmids are organised in a regulon that is composed of
several operons. Remarkably, there is a wide variation in the number and kind of establishment genes
on the different plasmids. Two fundamentally different regulatory mechanisms control the expression
of these regulons. Plasmids pLS20 and p576 are the two prototype plasmids reflecting these alternative
mechanisms. In the case of p576, the plasmid encodes a repressor protein (called Reg) that effectively
suppresses the establishment promoters. During the conjugation, the DNA but not the repressor is transferred.
Consequently, the establishment promoters are transiently active in the recipient cell until sufficient
repressor has been synthesised to repress them again. In the case of pLS20, the establishment genes
are preceded by a conserved large upstream element (CLUE) that most likely is responsible for transient
expression of the establishment genes by a yet unknown mechanism
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