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Domain 7:

Genetics and Genetic Tools

The Cytology of Bacterial Conjugation

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  • Authors: Matthew W. Gilmour1,5, Trevor D. Lawley2,5, and Diane E. Taylor3
  • Editor: James M. Slauch4
  • VIEW AFFILIATIONS HIDE AFFILIATIONS
    Affiliations: 1: Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada T6G 2R3; 2: Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada T6G 2R3; 3: Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada T6G 2R3; 4: The Schoold of Molecular and Cellular Biology, University of Illinois at Urbana-Champaign, Urbana, IL
  • Received 13 May 2004 Accepted 21 July 2004 Published 15 November 2004
  • Address correspondence to Diane E. Taylor Diane.Taylor@ualberta.ca
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  • Abstract:

    This review focuses on the membrane-associated structures present at cell-cell contact sites during bacterial conjugation. These transfer proteins/structures have roles in the formation and stabilization of mating contacts and ultimately the passage of substrate across the cell envelope between two bacterial cells. The review presents evidence for the dynamic interaction between donor and recipient cells, including the assembly of a transmembrane protein complex, and concludes with a refined model for the mechanism of bacterial conjugation. Bacterial conjugation, in addition to being a mechanism for genome evolution, can be considered as a mechanism for macromolecular secretion. In particular, plasmid-conjugative transfer is classified as a type IV secretion (T4S) system and represents the only known bacterial system for secretion of DNA. In all known conjugative transfer systems, a multitude of proteins are required for both plasmid transfer and pilus production. The plasmids discussed in the review include the F factor; the P group of plasmids, including RP4 and R751 (rigid); and the H plasmid group, including R27 (also thick flexible). With the LacI-GFP/ system, the F, P, and H plasmids were observed to reside at well-defined positions located at the mid and quarter-cell positions of throughout the vegetative cycle. In this review, recent observations based on bacterial cell biology techniques, including visualization of plasmid DNA and proteins at the subcellular level, have been combined with electron and light microscopy studies of mating cells to create an integrated overview of gram-negative bacterial conjugation, a concept referred to as the conjugative cycle.

  • Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3

Key Concept Ranking

Type III Secretion System
0.41259092
Type IV Secretion Systems
0.41227925
Outer Membrane Proteins
0.35280168
Transmission Electron Microscopy
0.34594807
0.41259092

References

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/content/journal/ecosalplus/10.1128/ecosalplus.2.2.3
2004-11-15
2017-11-21

Abstract:

This review focuses on the membrane-associated structures present at cell-cell contact sites during bacterial conjugation. These transfer proteins/structures have roles in the formation and stabilization of mating contacts and ultimately the passage of substrate across the cell envelope between two bacterial cells. The review presents evidence for the dynamic interaction between donor and recipient cells, including the assembly of a transmembrane protein complex, and concludes with a refined model for the mechanism of bacterial conjugation. Bacterial conjugation, in addition to being a mechanism for genome evolution, can be considered as a mechanism for macromolecular secretion. In particular, plasmid-conjugative transfer is classified as a type IV secretion (T4S) system and represents the only known bacterial system for secretion of DNA. In all known conjugative transfer systems, a multitude of proteins are required for both plasmid transfer and pilus production. The plasmids discussed in the review include the F factor; the P group of plasmids, including RP4 and R751 (rigid); and the H plasmid group, including R27 (also thick flexible). With the LacI-GFP/ system, the F, P, and H plasmids were observed to reside at well-defined positions located at the mid and quarter-cell positions of throughout the vegetative cycle. In this review, recent observations based on bacterial cell biology techniques, including visualization of plasmid DNA and proteins at the subcellular level, have been combined with electron and light microscopy studies of mating cells to create an integrated overview of gram-negative bacterial conjugation, a concept referred to as the conjugative cycle.

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Figures

Image of Figure 1
Figure 1

Plasmids encoding the RP4 were incubated with RP4-encoded relaxosomal proteins TraH, TraI, and TraJ. Arrows indicate bound Tra proteins. See reference 15 for additional details.

Reproduced with permission from E. Lanka.

Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3
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Image of Figure 2
Figure 2

The lower arrow indicates a newly synthesized pilus lacking absorbed Hgal phage. See reference 21 for additional details.

Reproduced with permission from the American Society for Microbiology.

Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3
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Image of Figure 3
Figure 3

Black arrows indicate recipient cells producing common pili and flagella, whereas donor cells are “bald” and indicated with white arrows. Donor cells contain a derepressed derivate of R27 and would produce few (0 to 4) pili under the conditions used. See reference 21 for additional details.

Reproduced with permission from the American Society for Microbiology.

Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3
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Image of Figure 4
Figure 4

Straight, closely appressed outer membranes are typical of junctions between bacteria in RP4-mediated mating with electron-dense material between outer membranes (arrow). The outer membrane (OM), periplasm (P), and cytoplasmic membrane (CM) are indicated. Bar, 25 nm. See reference 47 for additional details.

Reproduced with permission from the American Society for Microbiology.

Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3
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Image of Figure 5
Figure 5

Fluorescent microscopy of live cells harboring R27::. Bacteria were grown exclusively at 27°C and visualized under UV illumination. See references 42 and 52 for additional details.

Reproduced with permission from the American Society for Microbiology.

Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3
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Image of Figure 6
Figure 6

(A) The predicted transmembrane domains of the coupling protein TraD and Mpf protein TraB monomers are represented as cylinders, with N and C termini specified. The rigid conformation illustrated for TrhB is predicted from the high proline content in the primary sequence. (B) The multimeric state of the coupling protein (modeled after TrwB [see reference 57 ]) and the minimal multimeric state of TraB are shown. TraK, predicted to be the secretin molecule ( 10 , 33 ), is represented as a multimeric ring structure, modeled after the three-dimensional structure of dodecameric secretin PilQ ( 61 ). (C) A possible assembly of these proteins into a cell envelope-spanning pore-like superstructure is presented. Specific interactions are proposed or known to occur between the relaxase-coupling protein, coupling protein-TraB, TraB-TraK (see text). The outer membrane (OM), periplasm/peptidoglycan (P), and cytoplasmic membrane (CM) are indicated.

Reproduced with permission from the American Society for Microbiology.

Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3
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Image of Figure 7
Figure 7

GFP-LacI clusters on and results in a discrete GFP signal correlating to the position of the -labeled plasmid when live cells are viewed with fluorescence microscopy. Fluorescence micrographs show cells harboring (A) R751 and pSG20, (B) R751 only, (C–F) R751:: and pSG20 with foci located at the mid-cell (one focus), ¼ and ¾ (two foci), mid- and quarter-cell (three foci), and 1/5, 2/5, 3/5, and 4/5 (four foci) cellular positions. Experimental details have previously been described ( 71 ).

Reproduced with permission from the American Society for Microbiology.

Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3
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Image of Figure 8
Figure 8

The time (in minutes) at which the image was collected is indicated in the top left-hand corner. See reference 74 for additional details.

Reproduced with permission from the American Society for Microbiology.

Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3
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Image of Figure 9
Figure 9

Combined fluorescence/DIC micrographs of mating pairs: donor cells carrying R751:: are nonfluorescent, whereas recipient cells were producing GFP-LacI (uniformly green) and stained in the red membrane dye FM 4-64. Cultures were mixed and immediately immobilized in a nutrient agarose slab. Transconjugants have a red membrane signal but, instead of confluent green fluorescence, contain discrete GFP signals representing transferred R751:: molecules. Regions of direct contact between donors and transconjugants represent locations of mating pores through which DNA is transferred. Representative mating pairs of an unsuccessful mating pair (A) and successful mating pairs that are aligned with the lateral wall of donor and transconjugants in direct contact (B), with the pole of the donor in direct contact with the lateral wall of transconjugants (C), and with the lateral wall of the donor in direct contact with the pole of transconjugants (D). See reference 71 for additional details.

Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3
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Image of Figure 10
Figure 10

See text for details. Duration: approximately 51 seconds.

Citation: Gilmour M, Lawley T, Taylor D. 2004. The Cytology of Bacterial Conjugation, EcoSal Plus 2004; doi:10.1128/ecosalplus.2.2.3
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