The mismatch repair system (mutS and mutL) in Acinetobacter baylyi ADP1

Abstract

Background: Acinetobacter baylyi ADP1 is an ideal bacterial strain for high-throughput genetic analysis as the bacterium is naturally transformable. Thus, ADP1 can be used to investigate DNA mismatch repair, a mechanism for repairing mismatched bases. We used the mutS deletion mutant (XH439) and mutL deletion mutant (XH440), and constructed a mutS mutL double deletion mutant (XH441) to investigate the role of the mismatch repair system in A. baylyi. Results: We determined the survival rates after UV irradiation and measured the mutation frequencies, rates and spectra of wild-type ADP1 and mutSL mutant via rifampin resistance assay (Rif R assay) and experimental evolution. In addition, transformation efficiencies of genomic DNA in ADP1 and its three mutants were determined. Lastly, the relative growth rates of the wild type strain, three constructed deletion mutants, as well as the rifampin resistant mutants obtained from Rif R assays, were measured. All three mutants had higher survival rates after UV irradiation than wild type, especially the double deletion mutant. Three mutants showed higher mutation frequencies than ADP1 and favored transition mutations in Rif R assay. All three mutants showed increased mutation rates in the experimental evolution. However, only XH439 and XH441 had higher mutation rates than the wild type strain in Rif R assay. XH441 showed higher transformation efficiency than XH438 when donor DNA harbored transition mutations. All three mutants showed higher growth rates than wild-type, and these four strains displayed higher growth rates than almost all their rpoB mutants. The growth rate results showed different amino acid mutations in rpoB resulted in different extents of reduction in the fitness of rifampin resistant mutants. However, the fitness cost brought by the same mutation did not vary with strain background. Conclusions: We demonstrated that inactivation of both mutS and mutL increased the mutation rates and frequencies in A. baylyi, which would contribute to the evolution and acquirement of rifampicin resistance. The mutS deletion is also implicated in increased mutation rates and frequencies, suggesting that MutL may be activated even in the absence of mutS. The correlation between fitness cost and rifampin resistance mutations in A. baylyi is firstly established.

Novel tigecycline resistance mechanisms in Acinetobacter baumannii mediated by mutations in adeS, rpoB and rrf

“…Certain rpoB mutations have rather complex consequences and often lead to different physiological characteristics. Different mutations in the rpoB gene may induce biofilm formation, impair surface-associated motility, or reduce virulence together with an increase in fitness costs [51][52][53]. In this study, we confirmed the mutated rpoB (G136D) resulted in a decrease in susceptibility to tigecycline when investigating a genetically reconstructed strain containing the rpoB mutation only.…”

Genes and Proteomes Associated With Increased Mutation Frequency and Multidrug Resistance of Naturally Occurring Mismatch Repair-Deficient Salmonella Hypermutators

“…According to previous studies (LeClerc et al, 1996;Matic et al, 1997;Oliver et al, 2000;Eliopoulos and Blázquez, 2003;Jayaraman, 2009;Chu et al, 2017), mutations in the MutS, MutL, MutH, and UvrD proteins of the MMR system are the most important factors leading to hypermutability in bacteria. The mutation frequency in these strains ranged from 3.39 × 10 −4 to 5.46 × 10 −2 , which was increased by approximately 10 5 -to 10 6 -fold over the normal spontaneous mutation frequency of bacteria (LeClerc et al, 1996;Broaders et al, 2013;Zhou et al, 2020). In addition to high mutation frequency, MMR deficiency is associated with antibiotic susceptibility in hypermutators, and the hypermutators exhibit higher antibiotic resistance than normal bacteria (LeClerc et al, 1996;Oliver et al, 2002;Wilson et al, 2014).…”

“…Although many genetic deficiencies can lead to a hypermutable phenotype (LeClerc et al, 1996;Eliopoulos and Blázquez, 2003), hypermutation of bacteria is primarily caused by deficiencies in mutS, mutH, mutL, and mutU (uvrD) within the mismatch repair (MMR) system (LeClerc et al, 1996;Jayaraman, 2009;Veschetti et al, 2020). Mutations in these genes can result in increased mutation frequency and enhanced interspecies recombination (Verma et al, 2009;Zhou et al, 2020). Consequently, some genes encoding for antibiotic sensitivity and/or resistance, antibiotic uptake and/or efflux systems, or their regulatory factors can be altered in MMR-deficient bacteria (Eliopoulos and Blázquez, 2003;Fàbrega et al, 2009;Li et al, 2012;Zhou et al, 2020).…”

“…Mutations in these genes can result in increased mutation frequency and enhanced interspecies recombination (Verma et al, 2009;Zhou et al, 2020). Consequently, some genes encoding for antibiotic sensitivity and/or resistance, antibiotic uptake and/or efflux systems, or their regulatory factors can be altered in MMR-deficient bacteria (Eliopoulos and Blázquez, 2003;Fàbrega et al, 2009;Li et al, 2012;Zhou et al, 2020).…”

Isolation and Genomics of multidrug-resistant Brevundimonas diminuta collected from patients with pertussis-like symptoms

“…Rifampin is a synthetic derivative of natural products of the bacterium, with an inhibitory effect on beta-subunit of the RNA polymerase of prokaryotes and prescribed for gram-positive and gram-negative bacteria [59, 60]. Resistance to rifampicin (RIF) is mediated by mutations clustered in a small region of the rpoB gene [61, 62] which encodes the RNA polymerase β-subunit, or possibly by multidrug efflux pumps [59]. Previous studies confirmed mutation in the different amino acid sequences of rpoB protein mainly in 516, 526 and 536 mediated rifampin resistance in bacteria [60].…”