Abstract
Transposons are genetic elements that change their intracellular genomic position by transposition and are spread horizontally between bacteria when located on plasmids. It was recently discovered that transposition from fully heterologous DNA also occurs in the course of natural transformation. Here, we characterize the molecular details and constraints of this process using the replicative transposon Tn1 and the naturally competent bacterium Acinetobacter baylyi . We find that chromosomal insertion of Tn1 by transposition occurs at low but detectable frequencies and preferably around the A. baylyi terminus of replication. We show that Tn1 transposition is facilitated by transient expression of the transposase and resolvase encoded by the donor DNA. RecA protein is essential for the formation of a circular, double-stranded cytoplasmic intermediate from incoming donor DNA, and RecO is beneficial but not essential in this process. Absence of the recipient RecBCD nuclease stabilizes the double-stranded intermediate. Based on these results, we suggest a mechanistic model for transposition during natural transformation.
Highlights
Horizontal gene transfer drives bacterial evolution through the acquisition of novel genetic material and accelerates the spread of adaptive traits such as antimicrobial resistance (AMR) between bacteria [1]
We inserted the replicative transposon Tn1 into the narrow- host-range plasmid vector pACYC184 that replicates in Enterobacteriaceae but not in A. baylyi
This result indicates that Tn1 was chromosomally acquired by DNA uptake and transposition
Summary
Horizontal gene transfer drives bacterial evolution through the acquisition of novel genetic material and accelerates the spread of adaptive traits such as antimicrobial resistance (AMR) between bacteria [1]. The resulting circular plasmid pJK2 (Fig. 1) was used as donor DNA to naturally transform A. baylyi ADP1 wild-type cells. To compare this transposition frequency to extra-chromosomal plasmid establishment or to homologous recombination during natural transformation, we used circular plasmid DNA (RSF1010) or linear homologous DNA (pKH80-PCR) in transformation assays with A. baylyi and obtained frequencies of (5.4±1.1)×10−6 and (1.3±0.5)×10−4, respectively.
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