The conjugative transposon Tn925: enhancement of conjugal transfer by tetracycline in Enterococcus faecalis and mobilization of chromosomal genes in Bacillus subtilis and E. faecalis

Abstract

The effects of tetracycline on transfer of the conjugative, tetracycline-resistance transposon. Tn925, as well as the ability of the transposon to promote the transfer of chromosomal genes was examined in Enterococcus faecalis and Bacillus subtilis. To test for chromosomal transfer, multiply-marked strains of each organism, each carrying a single chromosomal copy of Tn925, were mated on filters with suitable recipient strains, under conditions where transformation and transduction were precluded. In both cases, transfer of a variety of chromosomal genes, at frequencies comparable to the frequency of Tn925 transfer, was detected readily. The presence of Tn925 in one of the members of the mating pair was absolutely required for chromosomal transfer, but transfer of Tn925 did not accompany every chromosomal transfer event. The results were consistent with a mating event resembling a type of cell fusion, allowing for extensive recombination between the genomes of the mating partners. Growth of Tn925-containing donor cells in the presence of tetracycline increased the transfer frequency of Tn925 by about tenfold in E. faecalis, but not in B. subtilis.

Circularization of Tn916 is required for expression of the transposon‐encoded transfer functions: characterization of long tetracycline‐inducible transcripts reading through the attachment site

“…We have demonstrated previously that the presence of tetracycline in the mating medium increased the transfer frequency of Tn1545 (Doucet-Populaire et al, 1991). This Molecular Microbiology (1998) 28(1), [103][104][105][106][107][108][109][110][111][112][113][114][115][116][117] ᮊ 1998 Blackwell Science Ltd observation has been confirmed for several Tn916-like elements (Torres et al, 1991;Rice et al, 1992), including the prototype element Tn916 (Showsh and Andrew, 1992), and it has been proposed that tetracycline-stimulated excision of the element would result in an increase in excision frequency and, in turn, in an increase in conjugation frequency (Manganelli et al, 1995). The molecular basis for this hypothesis would be that the tetracycline-inducible tetM transcript might activate the transcription of the downstream genes xis-Tn and int-Tn (Rice et al, 1992).…”

Tetracycline Antibiotics: Mode of Action, Applications, Molecular Biology, and Epidemiology of Bacterial Resistance

“…In cis, the transposon provides the proteins needed for transfer (257). The Tn916 family can mobilize plasmids in trans (48,183,297). Low levels of tetracycline increase the transfer of these genes and also increase the ability of the bacterial host to spread antibiotic resistance genes to other isolates, species, and genera (48,69,297).…”

“…The Tn916 family can mobilize plasmids in trans (48,183,297). Low levels of tetracycline increase the transfer of these genes and also increase the ability of the bacterial host to spread antibiotic resistance genes to other isolates, species, and genera (48,69,297). With their transfer ability, one might hypothesize that the ribosomal protection genes would be found in virtually all tetracycline-resistant genera examined; however, this is not the case (Tables 4 and 5).…”

“…The tet(M) gene can also be introduced into a significant number of other genera including gram-negative and gram-positive organisms and species lacking cell walls (18,24,69,237,274,297). In a majority of gram-positive species, the tet(M) gene is found in the chromosome, most often on conjugative elements (48,140,226).…”

Antibiotic resistance in Mexico: a brief overview of the current status and its causes

“…Perhaps some drugs that presumably promote the spread itself of resistance genes, such as quinolones [2] or tetracycline [3,4], are used more often in Latin America, hence enacting more than a mere selective pressure and increasing resistance rates when compared to low-usage countries. However, even if such a usage pattern difference exists, it is not likely to have a significant impact.…”