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Title:The Role of Plasmids in Microbial Secondary Metabolism
Author(s):Piwowarski, Janet Marie
Department / Program:Plant Pathology
Discipline:Plant Pathology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Agriculture, Plant Pathology
Abstract:Pseudomonas tabaci, P. angulata and P. coronafaciens are three closely related plant pathogens that differ only in their ability to produce the phytotoxin, tabtoxin, their resistance to tabtoxin, and their host specificity. The possibility that the genes for these characteristics were plasmid-borne was examined.
All nine strains of P. tabaci, P. angulata and P. coronafaciens contained a single plasmid DNA species. Attempts to eliminate the resident plasmid from one of these strains, P. tabaci ATCC 11528, using plasmid curing agents were not successful when loss of tabtoxin production was used as an indicator of plasmid loss. A mutant of P. tabaci ATCC 11528 was isolated which retained the resident plasmid, pathogenicity, and resistance to tabtoxin but had lost the ability to produce tabtoxin.
Physical characterization of the resident plasmids from these strains indicated that they harbored five different plasmid DNA species. P. tabaci ATCC 11528 and ATCC 11527 contained plasmid pJP1. A second, independent isolate of P. tabaci ATCC 11528 contained pJP1*, a plasmid in which a 3.9 Mdal piece of DNA appeared to have been inserted with pJP1. The insertion did not cause loss of pathogenicity traits or increased drug resistance in this strain. A third P. tabaci strain, ATCC 27881 harbored a plasmid, pJP27, indistinguishable, by restriction enzyme analysis, from the resident plasmid of three strains of P. angulata, ATCC 13453, 45 and 52. A strain of P. tabaci, BR(2), pathogenic on beans, contained a plasmid, pBW, that did not resemble pJP1, pJP1* or pJP27. P. coronafaciens 27 contained a fifth plasmid DNA species, pJP50, which did not resemble the other four plasmids.
Cross hybridization of restriction fragments of the five plasmids indicated that four of the five, pJP1, pJP1*, pJP27 and pJP50, contained regions of DNA sequence homology. Only PBW lacked sequence homology to the other plasmids. pJP1 hybridized to all sequences in pJP1* except those which contained only DNA from the 3.9 Mdal insertion. An 8.8 Mdal region was found to be homologous between pJP27 and pJP1. This region in pJP1 was the same region in which the pJP1* insertion was located. pJP50 also contained this 8.8 Mdal region as well as additional regions of sequence homology to each of these plasmids. The presence of highly conserved DNA species in P. tabaci, P. angulata and P. coronafaciens suggests that resident plasmids have an important, but as yet undefined role in these organisms.
Prior indirect evidence for the role of plasmids in streptomycin production and resistance in Streptomyces bikiniensis has been obtained using plasmid curing agents. Attempts to develop a reliable method for the isolation of sufficient quantities of plasmid DNA for the characterization of plasmids from S. bikiniensis and closely related streptomycin-producers were not successful. Two methods developed, however, allowed the isolation of what appeared to be plasmid DNA from these organisms as identicated by agarose gel electrophoresis; however, purified plasmid DNA could not be isolated by CsCl-ethidium bromide density gradients. The plasmid detected, pQS1, was approximately 30 Mdal and was present in S. bikiniensis, a dye-treated, "cured" derivative of this strain and two streptomycin-producing S. griseus strains, ATCC 11984 and ATCC 12475. The presence of pQS1 in the derivative of S. bikiniensis which lost the ability to produce streptomycin and streptomycin resistance when treated with plasmid curing agents, suggests that this plasmid does not contain the genes for these characters.
Issue Date:1980
Description:162 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
Other Identifier(s):(UMI)AAI8108629
Date Available in IDEALS:2014-12-14
Date Deposited:1980

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