Current Plasmid Research

Professor Eva Top ’s research is focused on the evolution and ecology of plasmids that transfer to and replicate in a broad range of bacterial hosts. These plasmids play an important role in the rapid adaptation of their hosts to changing environments. A good example is the current epidemic of antibiotic resistance in human pathogens, which is in part due to the spread of drug resistance plasmids.

Other Research
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FEMS Microbiology Ecology Progress towardsunderstanding the fate of plasmids in bacterial communities
Slater, Frances R.; Bailey, Mark J.; Tett, Adrian J.; Turner, Sarah L.. 2008. FEMS Microbiology Ecology.
doi: doi:10.1111/j.1574-6941.2008.00505.x
Abstract   √
Plasmid-mediated horizontal gene transfer influences bacterial community structure and evolution. However, an understanding of the forces which dictate the fate of plasmids in bacterial populations remains elusive. This is in part due to the enormous diversity of plasmids, in terms of size, structure, transmission, evolutionary history and accessory phenotypes, coupled with the lack of a standard theoretical framework within which to investigate them. This review discusses how ecological factors, such as spatial structure and temporal fluctuations, shape both the population dynamics and the physical features of plasmids. Novel data indicate that larger plasmids are more likely to be harboured by hosts in complex environments. Plasmid size may therefore be determined by environmentally mediated fitness trade-offs. As the correlation between replicon size and complexity of environment is similar for plasmids and chromosomes, plasmids could be used as tractable tools to investigate the influence of ecological factors on chromosomes. Parallels are drawn between plasmids and bacterial facultative symbionts, including the evolution of some members of both groups to a more obligate relationship with their host. The similarity between the influences of ecological factors on plasmids and bacterial symbionts suggests that it may be appropriate to study plasmids within a classical ecological framework.
 
Scientific Commons The mating pair formation system of conjugative plasmids — A versatile secretion machinery for transfer of proteins and DNA
Schröder, Gunnar, Lanka, Erich. 2005.
Available for download at Scientific Commons http://en.scientificcommons.org/20597825
Abstract   √
The mating pair formation (Mpf) system functions as a secretion machinery for intercellular DNA transfer during bacterial conjugation. The components of the Mpf system, comprising a minimal set of 10 conserved proteins, form a membrane-spanning protein complex and a surface-exposed sex pilus, which both serve to establish intimate physical contacts with a recipient bacterium. To function as a DNA secretion apparatus the Mpf complex additionally requires the coupling protein (CP). The CP interacts with the DNA substrate and couples it to the secretion pore formed by the Mpf system. Mpf/CP conjugation systems belong to the family of type IV secretion systems (T4SS), which also includes DNA-uptake and -release systems, as well as effector protein translocation systems of bacterial pathogens such as Agrobacterium tumefaciens (VirB/VirD4) and Helicobacter pylori (Cag). The increased efforts to unravel the molecular mechanisms of type IV secretion have largely advanced our current understanding of the Mpf/CP system of bacterial conjugation systems. It has become apparent that proteins coupled to DNA rather than DNA itself are the actively transported substrates during bacterial conjugation. We here present a unified and updated view of the functioning and the molecular architecture of the Mpf/CP machinery
 
Scientific Commons Early Stages of Conjugation in Escherichia R.coli
Curtiss, Roy, Caro, Lucien G., Allison, David P., Stallions, Donald. 1969.
Available for download at Scientific Commons http://en.scientificcommons.org/11712373
Abstract   √
We initiated these studies to learn more about the initial events during bacterial conjugation and to optimize conditions for their occurrence. We found that cells in donor cultures grown anaerobically prior to mating have (i) a higher mean number of F pili per cell, (ii) longer F pili, (iii) a higher probability of forming specific pairs with F− cells, and (iv) a faster rate of initiation of chromosome transfer than cells grown aerobically. The growth medium for the donor culture also influences these same parameters: a rich medium is superior to a completely synthetic medium. Starvation of donor cells in buffered saline or for a required amino acid results in (i) a loss of F pili, (ii) a loss in the ability of donor-specific phages to adsorb, (iii) a loss of ability to form specific pairs with F− cells and to yield recombinants, and (iv) an increase in recipient ability. These changes occur as a function of starvation time, and at rates which are dependent on the conditions of prior growth and starvation of the donor culture. Either treatment provides a rapid method for the production of F− phenocopies from donor cultures. Resynthesis of F pili by cells within a starved donor culture commences very soon after restoration of normal growth conditions, but full restoration of donor ability, as measured by recombinant yield, occurs at a slower rate. We found, along with other investigators, that F pili are essential for specific pair formation. We also found, however, that the presence of F pili is not sufficient for display of donor ability, nor is the absence of F pili enough for cells to exhibit recipient ability. This suggests, therefore, that one or more components, in addition to F pili, are necessary for the conversion of specific pairs to effective pairs (or for chromosome mobilization, or both) and for preventing donor cells from acting as recipients. On the basis of our results, we suggest optimal conditions for achieving high mating efficiencies.
 

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The Virtual Genome Project is funded by the National Science Foundation Microbial Genome Sequencing Program, Grant number: EF-0627988.
For more information contact: Dr. Eva Top, Professor of Biology, Department of Biological Sciences, University of Idaho, Moscow, I.D. 83844-3051 U.S.A.
email: etop [at] uidaho.edu

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