Meningococcal plasmids

In Neisseria meningitidis strains isolated from patients with meningococcal infection and from carriers, the presence of plasmids has been detected by the modified method of H. C. Bernboim and J. Doly. The strains have been studied with respect to their pathogenicity and sensitivity to antibacterial substances. No correlation between the presence of plasmids and pathogenicity factors, such as antilysozyme activity, the presence of hyaluronidase and the positive reaction to Congo red, resistance to penicillin, serogroup and the sources of isolation, has been established.     

Drug resistance plasmids

Conclusion The discovery of chemotherapeutic agents brought remarkable progress to the practice of medicine and to human and animal hygiene. In addition, improved sanitation and preventive medicine have protected human beings from infectious diseases caused by known pathogenic bacteria. As a result, the types of bacteria that play leading roles in infectious diseases have changed. These microoganisms readily cause infection, they are parasitic, and they carry multiple drug resistance as a result of the use of chemotherapeutic agents. Thus, mutiply resistant organisms have become prevalent and particular strains have become stabilized in hospitals and farms.The presence of conjugative (R) and nonconjugative (r) resistance plasmids in these bacterial strains has compounded the problems for the practice of medicine, livestock hygiene, and the fish culture industry. Rapid acquisition of drug resistance by bacteria and delays in finding new drugs have created new biological hazards for human beings.The discovery of resistance plasmids opened new research fields in genetics and molecular biology; it became clear that multiply resistant bacteria could develop quickly and spread rapidly all over the world. The genes governing replication, self-regulation, conjugal transmission and drug resistance, including transposon, are the most fascinating problems in biology. And the prevalence of drug resistance plasmids has broadened our perspective on the role that genetic exchanges play in the natural history of bacterial species.     

Microbial linear plasmids

While plasmids were originally considered to be generally circular until almost two decades ago, linear elements were reported to exist as well. They are now known to be common genetic elements in both, pro- and eukaryotes. Two types of linear plasmids exist, the so-called hairpin plasmids with covalently closed ends and those with proteins bound to their 5′ termini. Hairpin plasmids are common in human-pathogenic Borrelia spirochetes, in which they are instrumental in escape from the immunological response; cryptic hairpin elements are present in mitochondria of the plant pathogenic fungus Rhizoctonia solani. Plasmids with 5′ attached proteins constitute the largest group. In actinomycetous bacteria they are conjugative and usually confer advantageous phenotypes, e.g. formation of antibiotics, degradation of xenobiotics, heavy-metal resistance and growth on hydrogen as the sole energy source. In contrast, the majority of linear plasmids from eukaryotes are cryptic, with only a few exceptions. In some yeasts a killer phenotype may be associated, the most thoroughly investigated elements being those from Kluyveromyces lactis killer strains. In Neurospora spp. and in Podospora anserina, senescence and longevity respectively are correlated with linear plasmids. This review focuses on the biology of linear plasmids, their environmental significance and their use as tools in molecular and applied microbiology. Received: 15 November 1996 / Received revision: 23 December 1996 / Accepted: 30 December 1996     

Spot-transformation with plasmids

Summary A method is described which allows transformation of bacterial cells on the surface of agar plates. It is suitable for transferring large numbers of different plasmids, such as gene libraries, into a new genetic background. One nanogram of plasmid DNA is sufficient for transformation.     

Evolution of linear plasmids

Summary Linear plasmids are genetic elements commonly found in yeast, filamentous fungi, and higher plants. In contrast to all other plasmids they possess terminal inverted repeats and terminal bound proteins and encode their own DNA and RNA polymerases. Here we present alignments of conserved amino acid sequences of both the DNA and RNA polymerases encoded by those linear plasmids for which DNA sequence data are available. Additionally these sequences are compared to a number of polymerases encoded by related viral and cellular entities. Phylogenetic trees have been established for both types of polymerases. These trees appear to exhibit very similar subgroupings, proving the accuracy of the method employed.Abbreviations TIR terminal inverted repeats - mt mitochondrial - ORF open reading frame Offprint requests to: F. Kempken     

Bacteriocin plasmids ofPediococcus acidilactici

Summary Pediococcus acidilactici strains E, F and H isolated from fermented sausages produced bacteriocins which were protein in nature and inhibitory to a variety of spoilage and pathogenic microorganisms often encountered in foods. These strains harbored two to three plasmids ranging in size from 7.4 to 40.2 megadaltons. Curing experiments and plasmid profile analysis indicated the involvement of plasmid DNA with bacteriocin activity in all three strains. Carbohydrate fermentation and antibiotic resistance phenotypes did not appear to be associated with bacteriocin plasmids. Both bacteriocin activity and resistance determinants were linked in strain H and mediated by a 7.4-megadalton plasmid, whereas in strains E and F these two traits were not linked.     

Characterization of Propionibacterium plasmids

Plasmid DNAs from 15 Propionibacterium strains were characterized by using restriction endonuclease analyses, DNA-DNA hybridizations, and curing experiments. Restriction endonuclease analysis identified seven distinct plasmids (pRGO1 through pRGO7). Detailed restriction maps were constructed for four of these plasmids. DNA-DNA hybridization analysis revealed that plasmids pRGO1 and pRGO2 had extensive sequence homology and that both were homologous to pRGO7 and to similar sequences of pRGO5. Plasmids pRGO4 and pRGO6 did not have any significant sequence homology with any of the other plasmids. Plasmid pRGO3 had partial sequence homology only with pRGO7. Curing of plasmids pRGO1, pRGO2, and pRGO5 was achieved by treatment with acriflavin, but we failed to identify any plasmid-encoded bacteriocin production, carbohydrate fermentation, or antibiotic resistance. However, physical evidence was obtained that tentatively linked the clumping phenotype of Propionibacterium jensenii P38 with plasmid pRGO5.     

The use of mini-Gal plasmids for rapid incompatibility grouping of conjugative R plasmids

The galactose operon of Escherichia coli K-12 has been used as a phenotypic marker for miniplasmids derived in vitro from R plasmids representing six incompatibility groups. This has enabled the development of a rapid incompatibility typing scheme in which the miniplasmids are used as incompatibility exemplars, their presence in strains being monitored on galactose fermentation indicator media.     

Colicin V virulence plasmids.

ColV plasmids are a heterogeneous group of IncFI plasmids which encode virulence-related properties such as the aerobactin iron uptake system, increased serum survival, and resistance to phagocytosis. These plasmids have been found in invasive strains of Escherichia coli which infect vertebrate hosts including humans and livestock. Colicin V was the first colicin to be identified, in 1925, but not until the field experienced a renewed interest has the mechanism of colicin V activity been explored. As encoded by ColV plasmid pColV-K30, the aerobactin iron uptake system has been extensively investigated, but other ColV-encoded phenotypes remain largely uncharacterized. Restriction enzyme mapping of the 144-kb pColV-K30 and of the 80-kb pColV-B188 has facilitated systematic study, so that questions can be addressed by a molecular and comparative approach regarding the contributions of individual factors and plasmids to the virulence of host E. coli in model systems. The family of large ColV plasmids could be analogous to other families of large virulence plasmids, and insights gained from studying these plasmids should contribute to our understanding of cross-genetic interactions and the role of large plasmids in bacterial pathogenesis.     

Large plasmids in an actinomycete

Abstract Using a modified procedure large indigenous plasmids were detected in cells of three strains belonging to a group of phenotypically similar actinomycetes isolated from the rhizoplane and root nodules of Alnus spp. M _r values of the plasmids were estimated to be about 80 · 10⁶ and 120 · 10⁶. The plasmid profiles of different strains of the group were found to be almost identical. This remarkable plasmid similarly is discussed in relation to the common source of isolation.