Outcomes and characterization of chromosomal self-targeting by native CRISPR-Cas systems in Streptococcus thermophilus.
FEMS Microbiol Lett
; 366(9)2019 05 01.
Article
en En
| MEDLINE
| ID: mdl-31077282
ABSTRACT
CRISPR-Cas systems provide adaptive immunity against phages in prokaryotes via DNA-encoded, RNA-mediated, nuclease-dependent targeting and cleavage. Due to inefficient and relatively limited DNA repair pathways in bacteria, CRISPR-Cas systems can be repurposed for lethal DNA targeting that selects for sequence variants. In this study, the relative killing efficiencies of endogenous Type I and Type II CRISPR-Cas systems in the model organism Streptococcus thermophilus DGCC7710 were assessed. Additionally, the genetic and phenotypic outcomes of chromosomal targeting by plasmid-programmed Type I-E or Type II-A systems were analyzed. Efficient killing was observed using both systems, in a dose-dependent manner when delivering 0.4-400 ng of plasmid DNA. Targeted PCR screening and genome sequencing were used to determine the genetic basis enabling survival, showing that evasion of Type I-E self-targeting was primarily the result of low-frequency defective plasmids that excised the targeting spacer. The most notable genotype recovered from Type II-A targeting of genomic locus, lacZ, was a 34 kb-deletion derived from homologous recombination (HR) between identical conserved sequences in two separate galE coding regions, resulting in 2% loss of the genome. Collectively, these results suggest that HR contributes to the plasticity and remodeling of bacterial genomes, leading to evasion of genome targeting by CRISPR-Cas systems.
Palabras clave
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Bacteriófagos
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Cromosomas Bacterianos
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Streptococcus thermophilus
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Sistemas CRISPR-Cas
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Edición Génica
Idioma:
En
Revista:
FEMS Microbiol Lett
Año:
2019
Tipo del documento:
Article
País de afiliación:
Estados Unidos