Shoemaker N B, Salyers A A
Department of Microbiology, University of Illinois, Urbana 61801.
J Bacteriol. 1990 Apr;172(4):1694-702. doi: 10.1128/jb.172.4.1694-1702.1990.
A 65-kilobase-pair element, XBU4422, which has some transposonlike characteristics but carries no known antibiotic resistance genes, has been isolated from Bacteroides uniformis 0061. XBU4422 was trapped on Bacteroides-Escherichia coli shuttle vectors during experiments in which one of the conjugal Bacteroides tetracycline resistance (Tcr) elements was being used to mobilize the shuttle vectors to Bacteroides recipients. Results of Southern hybridization experiments showed that XBU4422 is normally integrated in the B. uniformis 0061 chromosome and is found only in some strains. Insertion of XBU4422 in the shuttle vectors was site specific and orientation specific. Nonmobilizable vectors that had acquired XBU4422 became transmissible and could be transferred to Bacteroides or E. coli recipients. In B. uniformis transconjugants, the XBU4422 insertion in the vectors was usually intact, but XBU4422 was always lost in matings with E. coli, Bacteroides thetaiotaomicron, or B. ovatus. The loss of XBU4422 did not visibly alter the vector; in the case of E. coli, the loss of the insertion appeared to be RecA dependent. Although XBU4422 carried no antibiotic resistances, it shared regions of homology with six conjugal Bacteroides Tcr elements; this homology was strongest with the ends of XBU4422. Using a strain of B. thetaiotaomicron that contains no XBU4422-hybridizing sequences, we showed that the ends of XBU4422 were probably reacting with the ends of the Tcr elements. These results provide the first direct evidence that the Tcr elements, like XBU4422, are integrated in the chromosome and that insertion of the least some Tcr elements, such as TcrEmr DOT, is relatively site specific.
一个65千碱基对的元件XBU4422已从均匀拟杆菌0061中分离出来，它具有一些转座子样特征，但未携带已知的抗生素抗性基因。在实验中，当其中一个接合型拟杆菌四环素抗性（Tcr）元件用于将穿梭载体转移至拟杆菌受体时，XBU4422被困在了拟杆菌-大肠杆菌穿梭载体上。Southern杂交实验结果表明，XBU4422通常整合在均匀拟杆菌0061染色体中，且仅在一些菌株中发现。XBU4422在穿梭载体中的插入是位点特异性和方向特异性的。获得XBU4422的不可移动载体变得可转移，并可转移至拟杆菌或大肠杆菌受体。在均匀拟杆菌转接合子中，载体中的XBU4422插入通常是完整的，但在与大肠杆菌、嗜水气单胞菌或卵形拟杆菌交配时，XBU4422总是会丢失。XBU4422的丢失并未明显改变载体；就大肠杆菌而言，插入的丢失似乎依赖于RecA。尽管XBU4422不携带抗生素抗性，但它与六个接合型拟杆菌Tcr元件具有同源区域；这种同源性在XBU4422的末端最强。使用一株不含XBU4422杂交序列的嗜水气单胞菌，我们表明XBU4422的末端可能与Tcr元件的末端发生反应。这些结果提供了首个直接证据，表明Tcr元件与XBU4422一样，整合在染色体中，并且至少一些Tcr元件（如TcrEmr DOT）的插入相对位点特异性。
