Plasmids incompatibility

Plasmid incompatibility is a situation where plasmids that replicate themselves in similar ways cannot coexist in the same bacterial cell because of forced competition for replication proteins and RNA. Apramycin 18 mimics the function of a small piece of RNA that dictates incompatibility with an ampicillin-resistance plasmid and triggers the eviction of those plasmids from the bacterial cells rendering them susceptible to ampicillin treatment. 

Ultimately a plasmid is defined by its mode of DNA repHcation. DNA repHcation is initiated at a single, characteristic sequence, termed the origin. The origin sequence determines the copy number of the plasmid relative to the host chromosome and the host enzymes that are involved in plasmid repHcation. Two different plasmids that contain the same origin sequence are termed incompatible. This term does not refer to the active exclusion of one plasmid by another from the ceU but rather to a stochastic process by which the two plasmids are partitioned differentially into progeny ceUs. A ceU which contains two plasmids of the same incompatibiHty group segregates two clonal populations, each of which has one of the two plasmids in it. 

Briaux S, Gerbaud G, Jaffe-Brachet A. 1979. Studies of a plasmid coding for tetracycline resistance and hydrogen sulfide production incompatible with the prophage PI. Mol Gen Genet 170 319-325. 

Pinney, R.J. (1980). Distribution among incompatibility groups of plasmids that confer UV mutability and UV resistance. Mutation Res. 72 155-159. 

Many destination vectors are commercially available. However, it is also possible to construct a destination vector that is suitable for individual experiments. To constrnct snch vectors, one should insert the rr ffi-containg cassette (commercially available from Invitrogen) into the appropriate locns of a Gateway-incompatible vector. The resultant plasmids can be amplified only in the DB3.I strain, due to the toxic ccd gene (7). 

Plasmids usually resemble chromosomes except that they are approximately 0.1-1.0% of the size of a bacterial chromosome, and there are a few that are linear rather than circular. Plasmid genes are not essential for the normal functioning of the cell but may code for a property that affords a survival advantage in certain environmental conditions bacteria possessing the plasmid in question would therefore be selected when such conditions exist. Properties which can be coded by plasmids include the ability to utilize unusual sugars or food sources, toxin production, production of pili that facilitate the attachment of a cell to a substrate (e.g. intestinal epithelium) and antibiotic resistance. A cell may contain multiple copies of any one plasmid and may contain two or more different plasmids. However, some plasmid combinations cannot co-exist inside the same cell and are said to be incompatible this phenomenon enables plasmids to be classified into incompatibility groups. 

One or more plasmids are usually found in clinical isolates of S. aureus. There are at least three families of S. aureus plasmids (Novick 1990), which are classified into fifteen incompatibility groups (Novick 1987). Most plasmids that have been desaibed encode antimicrobial resistance determinants, and some have also been attributed other clinically significant properties, such as toxin production (e.g. entero-toxins SED and SEJ, and exfoliative toxin ETB), whereas some staphylococcal plasmids are phenotypically cryptic. 

A good example of a bulk separation are the aqueous two-phase systems (ATPS). They can be used as an alternative and efficient approach for purification of biomolecules by partitioning between two liquid phases. ATPS result from the incompatibility of polymers, either between two polymers in water or a polymer solution with a salt solution. In this system, the cells are considered to be immobilized on to one of the phases of the ATPS and the required product is made to partition into the other phase by proper manipulation of the system. ATPS can be used to purify proteins, cells,viruses particles and plasmid DNA. °... 

Plasmids of the incompatibility groups C, N, P, Q and W exhibit a host range much widm than those commonly used as iq>licons for E. co/l-specific vectors. Their properties have been reviewed in several recent articles that provide lists of vectors and hosts (34,48,49). Vectors based on IncP and IncQ replicons are among the most highly developed broad-host-range vectors available to date. For some of them, such as pMMB66 and pMMB207 smes the entire nucleotide sequence has been determined (34). 

Gupta, A., Phung, L.T., Taylor, D.E., and Silver, S. (2001) Diversity of silver resistance genes in IncH incompatibility group plasmids. Microbiology, 147, 3393-3402. 

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