Open AccessPossible Origins of CTnBST, a Conjugative Transposon Found Recently in a Human Colonic Bacteroides Strain
Author(s) -
David Schlesinger,
Nadja B. Shoemaker,
Abigail A. Salyers
Publication year - 2007
Publication title -
applied and environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.552
H-Index - 324
eISSN - 1070-6291
pISSN - 0099-2240
DOI - 10.1128/aem.00455-07
Subject(s) - transposable element , bacteroides , biology , bacteroides fragilis , gene , genetics , microbiology and biotechnology , horizontal gene transfer , insertion sequence , genome , bacteroides thetaiotaomicron , mobile genetic elements , plasmid , bacteria
A previous survey ofBacteroides isolates suggested that theermB gene enteredBacteroides spp. recently. Previously,ermB had been found almost exclusively in gram-positive bacteria. In oneBacteroides strain,ermB was located on 100-kb conjugative transposon (CTn) CTnBST. To assess the possible origin of this CTn, we obtained the full DNA sequence of CTnBST and used this information to investigate its possible origins. Over one-half of CTnBST had high sequence identity to a putative CTn found in the genome ofBacteroides fragilis YCH46. This included the ends of the CTn and genes involved in integration, transfer, and excision. However, the region around theermB gene contained genes that appeared to originate from gram-positive organisms. In particular, a 7-kb segment containing theermB gene was 100% identical to anermB region found in the genome of the gram-positive bacteriumArcanobacterium pyogenes . A screen ofBacteroides isolates whose DNA cross-hybridized with a CTnBST probe revealed that several isolates did not carry the 7-kb region, implying that the acquisition of this region may be more recent than the acquisition of the entire CTnBST element byBacteroides spp. We have also identified otherBacteroides isolates that carry a slightly modified 7-kb region but have no other traces of CTnBST. Thus, it is possible that this 7-kb region could itself be part of a mobile element that has inserted in aBacteroides CTn. Our results show that CTnBST is a hybrid element which has acquired a portion of its coding region from gram-positive bacteria but which may originally have come fromBacteroides spp. or some related species.