Mobilization of Bacteroides plasmids by Bacteroides conjugal elements

Valentine, P J; Shoemaker, Nadja B.; Salyers, Abigail A.

doi:10.1128/jb.170.3.1319-1324.1988

Cited by 123 publications

(97 citation statements)

References 15 publications

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“…That is, pregrowth of strains carrying the elements on low levels of tetracycline (1 ,ug/ml) results in enhancement of the frequency of self-transfer of the element and of the frequency of mobilization of coresident plasmids. One exception is the Tcr Emr element designated Tcr Emr 12256 by Shoemaker et al (16,22). This element exhibits constitutive transfer and mobilization.…”

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“…Both types are capable not only of transferring themselves from one Bacteroides strain to another but also of mobilizing coresident plasmids from Bacteroides donors to Bacteroides or Escherichia coli recipients (13,22). Most Tcr elements exhibit tetracycline regulation of self-transfer and mobilization (4,8,13,22,23). That is, pregrowth of strains carrying the elements on low levels of tetracycline (1 ,ug/ml) results in enhancement of the frequency of self-transfer of the element and of the frequency of mobilization of coresident plasmids.…”

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The region of a Bacteroides conjugal chromosomal tetracycline resistance element which is responsible for production of plasmidlike forms from unlinked chromosomal DNA might also be involved in transfer of the element

1990

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Large (>50 kilobases) conjugal chromosomal tetracycline resistance (Tc') elements have been found in many human colonic Bacteroides strains. Recently, N. B. Shoemaker and A. A. Salyers (J. Bacteriol. 170:1651-1657 reported that some of these Tcr elements appeared to mediate production of plasmidlike forms, NBU1 and NBU2, from an unlinked region of the chromosome of Bacteroides uniformis 0061. Production of the plasmidlike forms and the transfer frequency of the Tcr elements were both enhanced by preexposure to tetracycline. Thus it appeared that genes involved in production of plasmidlike forms (Plf activity) might be coregulated with transfer genes and that Plf activity might have a role in transfer of the Tcr elements. By screening subclones of a Tcr element, Tcr Emr DOT, we have shown that the genes necessary for Plf activity on the Tcr element are within a 10-kilobase region adjacent to the Tcr gene. Subclones of this region were then used to construct insertional gene disruptions in a Tcr element, Tcr ERL, which is closely related to the Tcr Emr DOT element. Two of the disruption mutants were Plf-. Both had reduced transfer frequencies, one (Q1RDB2) 102-fold lower than that of the wild-type element and the other (QRDBT) 104-fold lower. QlRDB2 was also deficient in the ability to mobilize coresident plasmids, whereas QRDBT exhibited nearly wild-type mobilization activity. The phenotypes of the mutants indicate that there are at least two genes necessary for Plf activity and that both may be involved in transfer of the element. The third disruption mutant (fQRDB1), which expressed Plf constitutively, also had a transfer frequency 102-fold lower than that of the wild-type element and was deficient in mobilization of coresident plasmids. The relationship between Plf genes and transfer, therefore, appears to be a complex one.

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The region of a Bacteroides conjugal chromosomal tetracycline resistance element which is responsible for production of plasmidlike forms from unlinked chromosomal DNA might also be involved in transfer of the element

1990

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“…Escherichia coli strains were grown in Luria broth or Luria broth agar plates. Bacteroides strains were grown in prereduced trypticase-yeast extract-glucose broth or agar (11,17).…”

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“…A plasmid containing the largest insert (approximately 9 kbp of NBU2) was chosen for further study. Matings were done as described previously (7,17). Various subclones of the cloned region were tested for mobilization by the IncP plasmids R751 and RP4.…”

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The mobilization regions of two integrated Bacteroides elements, NBU1 and NBU2, have only a single mobilization protein and may be on a cassette

Shoemaker

Wang

et al. 1995

J Bacteriol

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Bacteroides conjugative transposons can act in trans to excise, circularize, and transfer unlinked integrated elements called NBUs (for nonreplicating Bacteroides units). Previously, we localized and sequenced the mobilization region of one NBU, NBU1, and showed that this mobilization region was recognized by the IncP plasmids RP4 and R751, as well as by the Bacteroides conjugative transposons. We report here that the single mobilization protein carried by NBU1 appears to be a bifunctional protein that binds to the oriT region and catalyzes the nicking reaction that initiates the transfer process. We have also localized and sequenced the mobilization region of a second NBU, NBU2. The NBU2 mobilization region was 86 to 90% identical at the DNA sequence to the oriT-mob region of NBU1. The high sequence similarity between NBU1 and NBU2 ended abruptly after the stop codon of the mob gene and about 1 kbp upstream of the oriT region, indicating that the oriT-mob regions of NBU1 and NBU2 may be on some sort of cassette. A region on NBU1 and NBU2 which lies immediately upstream of the oriT region had 66% sequence identity to a region upstream of the oriT region on a mobilizable transposon, Tn4399, an element that had previously appeared to be completely unrelated to the NBUs.Many Bacteroides clinical isolates carry large (Ͼ70-kbp) integrated self-transmissible elements, called conjugative transposons (2, 11). These elements have also been called Tc r elements because most of them carry a tetracycline resistance (Tc r ) gene, tetQ. Bacteroides Tc r elements have an unusual activity not reported for any other known conjugative transposon. They act in trans to excise and mobilize smaller unlinked DNA elements called NBUs (nonreplicating Bacteroides units) ( Fig. 1) (1,12,13,16,17). Two NBUs, NBU1 and NBU2, have been characterized (12, 13). These NBUs are 10 to 12 kbp in size and appear to be unrelated to the conjugative transposons that excise and mobilize them (12). During transfer, the NBUs are excised from the chromosome to form a double-stranded circle, which is the transfer intermediate ( Fig. 1) (7, 13). The circular form of the NBU then uses the transfer pore provided by the conjugative transposon to move into a recipient cell (7). The Bacteroides conjugative transposons also enhance, by at least 1000-fold, the transfer frequency of another integrated element, the mobilizable transposon Tn4399 (5, 8). Results of previous studies had indicated that Tn4399 was not related to the NBUs. For example, Tn4399 has a different mode of integration than that of the NBUs, and the mobilization region of Tn4399 had no significant sequence similarity to the mobilization region of the NBUs (6, 7, 13). In this report, we provide the first evidence that Tn4399 and the NBUs do in fact share some sequence similarity.The oriT-mob region of NBU1 allows NBU1 to be mobilized not only by Bacteroides conjugative transposons but also by the IncP plasmids R751 and RP4 (7). Thus, mobilization of the NBU1 circle form by IncP plasmids presumably ...

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Strategies to Prevent the Spread of Antibiotic Resistance

Aminov

2019

Antibiotic Drug Resistance

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Mobilization of Bacteroides plasmids by Bacteroides conjugal elements

Cited by 123 publications

References 15 publications

The region of a Bacteroides conjugal chromosomal tetracycline resistance element which is responsible for production of plasmidlike forms from unlinked chromosomal DNA might also be involved in transfer of the element

The region of a Bacteroides conjugal chromosomal tetracycline resistance element which is responsible for production of plasmidlike forms from unlinked chromosomal DNA might also be involved in transfer of the element

The mobilization regions of two integrated Bacteroides elements, NBU1 and NBU2, have only a single mobilization protein and may be on a cassette

Strategies to Prevent the Spread of Antibiotic Resistance

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