<i>Escherichia coli</i>is naturally transformable in a novel transformation system

Sun, Dongchang; Zhang, Yanmei; Mei, Yadong; Jiang, Huiling; Xie, Zhaoxiong; Liu, Huihui; Chen, Xiangdong; Shen, Ping

doi:10.1111/j.1574-6968.2006.00503.x

Cited by 41 publications

(57 citation statements)

References 22 publications

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“…This observation contrasts the studies reporting the ability of some bacterial species present in the GIT to become naturally transformed in vitro (Mercer et al, 1999a;Sun et al, 2006). Likely explanations for this non-uniform knowledge state include: (i) methodological limitations to the GIT sample size that can be practically analyzed for low frequency transfer events; (ii) a lack of understanding of ecological processes in the GIT limiting our ability to design biologically and tempo-spatially relevant HGT investigations; (iii) unidentified processes in the GIT that shields or adsorb DNA molecules during degradation process preventing measurable exposure to competent bacteria; or (iv) lack of competence development in naturally transformable bacteria in the GIT.…”

Section: Discussioncontrasting

confidence: 94%

Lack of detectable DNA uptake by bacterial gut isolates grownin vitroand byAcinetobacter baylyicolonizing rodentsin vivo

Nordgård¹,

Nguyen

Midtvedt

et al. 2007

Environ. Biosafety Res.

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Biological risk assessment of food containing recombinant DNA has exposed knowledge gaps related to the general fate of DNA in the gastrointestinal tract (GIT). Here, a series of experiments is presented that were designed to determine if genetic transformation of the naturally competent bacterium Acinetobacter baylyi BD413 occurs in the GIT of mice and rats, with feed-introduced bacterial DNA containing a kanamycin resistance gene (nptII). Strain BD413 was found in various gut locations in germ-free mice at 10 3 −10 5 CFU per gram GIT content 24-48 h after administration. However, subsequent DNA exposure of the colonized mice did not result in detectable bacterial transformants, with a detection limit of 1 transformant per 10 3 −10 5 bacteria. Further attempts to increase the likelihood of detection by introducing weak positive selection with kanamycin of putative transformants arising in vivo during a 4-week-long feeding experiment (where the mice received DNA and the recipient cells regularly) did not yield transformants either. Moreover, the in vitro exposure of actively growing A. baylyi cells to gut contents from the stomach, small intestine, cecum or colon contents of rats (with a normal microbiota) fed either purified DNA (50 µg) or bacterial cell lysates did not produce bacterial transformants. The presence of gut content of germfree mice was also highly inhibitory to transformation of A. baylyi, indicating that microbially-produced nucleases are not responsible for the sharp 500-to 1 000 000-fold reduction of transformation frequencies seen. Finally, a range of isolates from the genera Enterococcus, Streptococcus and Bifidobacterium spp. was examined for competence expression in vitro, without yielding any transformants. In conclusion, model choice and methodological constraints severely limit the sample size and, hence, transfer frequencies that can be measured experimentally in the GIT. Our observations suggest the contents of the GIT shield or adsorb DNA, preventing detectable exposure of feed-derived DNA fragments to competent bacteria.

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Section: Discussioncontrasting

confidence: 94%

Lack of detectable DNA uptake by bacterial gut isolates grownin vitroand byAcinetobacter baylyicolonizing rodentsin vivo

Nordgård¹,

Nguyen

Midtvedt

et al. 2007

Environ. Biosafety Res.

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“…Although several studies of Escherichia coli have identified conserved homologues of all genes required by most competent bacteria to take up DNA (12,15,22,59), researchers have for decades struggled to demonstrate that E. coli takes up and recombines chromosomal DNA, and introduction of plasmids into E. coli cells relies on artificial permeabilization by calcium chloride or on electroporation. Although more "natural" variants of these techniques have been reported (7,8,10,82), no competence genes have been implicated, and a recent study found that plasmid transformation of E. coli on agar plates does not require four putative competence genes whose homologues are essential for DNA uptake in other bacteria (70).…”

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confidence: 99%

Sxy Induces a CRP-S Regulon in Escherichia coli

2009

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Escherichia coli is not considered naturally competent, yet it has homologues of the genes that most competent bacteria use for DNA uptake and processing. In Haemophilus influenzae and Vibrio cholerae, these genes are regulated by the Sxy and cyclic AMP receptor (CRP) proteins. We used microarrays to find out whether similar regulation occurs in E. coli. Expression of sxy strongly induced 63 transcriptional units, 34 of which required CRP for transcriptional activation and had promoter sites resembling the Sxy-and CRPdependent CRP-S motif previously characterized in H. influenzae. As previously reported, sxy expression also induced the sigma-H regulon. Flagellar operons were downregulated by sxy expression, although motility remained unaffected. The CRP-S regulon included all of E. coli's known competence gene homologues, so we investigated Sxy's effect on competence-associated phenotypes. A sxy knockout reduced both "natural" plasmid transformation and competitive fitness in long-term culture. In addition, expression of plasmid-borne sxy led to production of type IV pilin, the main subunit of the DNA uptake machinery of most bacteria. Although H. influenzae Sxy only weakly activated the E. coli Sxy regulon, induction was dramatically improved when it was coexpressed with its cognate CRP, suggesting that intimate interactions between Sxy and CRP are required for transcriptional activation at CRP-S sites.

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“…In this study, natural transformation of E. coli isolates was done using the transformation system described by Sun et al [8]. The results demonstrated that the integron-containing DNA from the seven donors could be transferred to E. coli J53Az r in this transformation system with the transformation frequency of 10 -7 to 10 -5 ( Table 3).…”

Section: Natural Transformationmentioning

confidence: 89%

“…The plasmids isolated from seven integron-positive strains were subjected to natural transformation with E. coli J53Az r as the recipient followed the previously described protocol [8]. The recipient strain was grown overnight in LB broth (to reach a density of 10…”

Section: Natural Transformation Of E Colimentioning

confidence: 99%

“…In previous studies, natural transformation of E. coli can be implemented by various artificial transformation methods [5][6][7]. Recently, a transformation system for E. coli that is completely different from the traditional methods has been reported [8]. In this system, non-physiological factors (e.g., a high Ca 2+ concentration, incubation at a low temperature, a temperature shift, and an electronic shock in electroporation) are not necessary.…”

Section: Introductionmentioning

confidence: 99%

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Characterization and horizontal transfer of class 1 integrons in Escherichia coli isolates from cooked meat products

Zhang

Jiang

et al. 2016

J Infect Dev Ctries

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Introduction: Escherichia coli is a commensal bacterium in humans, animals, and the environment that is one of the microorganisms commonly resistant to antimicrobials. Cooked meat products, which are popular in China, are easily contaminated by E. coli during processing and storage. Methodology: In this study, a total of 75 E. coli isolates from cooked meat products in Henan province, China, were assayed for the presence of and horizontal transfer of class 1 integrons. Results: Class 1 integrons were detected in 11 (14.7%) of these isolates, and contained four groups of resistance gene cassettes, including dfrA17-aadA5, dfrA1-aadA1, dfrA12-orfF-aadA2, and an uncommon array of aacA4-catB8-aadA1. The transfer frequency of selected integron-positve donors ranged from 10 -6 to 10 -4 transconjugants per recipient cell, and the integron-containing DNA from the donors could be transferred to E. coli J53Az r with the transformation frequency of 10 -7 to 10 -5 . Conclusions: Class 1 integrons could be transferred to recipient E. coli J53 by conjugation and natural transformation. These findings suggest the role of commensal E. coli isolates from cooked meats as an important reservoir for integrons and the possible transfer of antimicrobial resistance genes to humans via the food chain.

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Escherichia coliis naturally transformable in a novel transformation system

Cited by 41 publications

References 22 publications

Lack of detectable DNA uptake by bacterial gut isolates grownin vitroand byAcinetobacter baylyicolonizing rodentsin vivo

Lack of detectable DNA uptake by bacterial gut isolates grownin vitroand byAcinetobacter baylyicolonizing rodentsin vivo

Sxy Induces a CRP-S Regulon in Escherichia coli

Characterization and horizontal transfer of class 1 integrons in Escherichia coli isolates from cooked meat products

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