A Multicomponent System Is Required for Tetracycline-Induced Excision of Tn 4555

• Published in: Journal of bacteriology Vol. 186; no. 2; pp. 438 - 444
• Main Authors: Parker, Anita C., Smith, C. Jeffrey
• Format: Journal Article
• Language: English
• Published: 15-01-2004
• ISSN: 0021-9193; 1098-5530
• DOI: 10.1128/JB.186.2.438-444.2004

Bacteroides
spp. are the predominant organisms in the intestinal tract, and they also are important opportunistic pathogens. Antibiotic therapy of
Bacteroides
infections often is complicated by the prevalence of drug-resistant organisms which acquire resistance genes from a variety of mobile genetic elements including conjugative transposons (CTns) and mobilizable transposons (MTns). Tn
4555
is an MTn that encodes β-lactam resistance, and it is efficiently mobilized by the
Bacteroides
CTns via a tetracycline (TET)-inducible mechanism. In this study a model system with CTn341 and a Tn
4555
minielement was used to examine Tn
4555
excision from the chromosome. Using PCR and mobilization assays it was established that excision was stimulated by TET in the presence of CTn341. In order to determine which Tn
4555
genes were required for excision,
int
,
tnpA
,
tnpC
,
xis
, and
mobA
mutants were examined. The results indicated that
int
plus two additional genes,
tnpC
and
xis
, were required for optimal excision. In addition, there was no requirement for the
mobA
gene, as had been shown for another MTn, NBU1. The Xis protein sequence is related to a family of plasmid excisionases, but the TnpC gene product did not match anything in the sequence databases. Evidence also was obtained that suggested that Xis is involved in the control of TET-induced excision and in control of mobilization by CTn341. Overall, these results indicate that excision of MTns is a complex process that requires multiple gene products.