|
In some instances, plasmids
may harbor a number of genes encoding resistance to different antibiotics
(multidrug resistance).
Table 2
|
Examples of
Naturally Occurring Plasmids and Relevant Features
|
|
|
|
Plasmid
|
|
|
|
Plasmid
|
Host
|
size (kbp)
|
Relevant feature
|
Ref.
|
|
pT181
|
Staphylococcus
aureus
|
4.4
|
Tetracycline resistance
|
19
|
|
pRN1
|
Sulfolobus
islandicusa
|
5.4
|
—
|
20
|
|
2\x
|
Saccharomyces
cerevisiaeb
|
6.3
|
—
|
21
|
|
ColEl
|
Escherichia
coli
|
6.6
|
Colicin production and
|
9
|
|
|
|
|
immunity
|
|
|
pMBl
|
Escherichia
coli
|
8.5
|
EcoRI restriction-
|
22
|
|
|
|
|
modification system
|
|
|
pGKL2
|
Kluyveromyces
lactisb
|
13.5
|
Killer plasmid
|
23
|
|
pAMpi
|
Enterococcus
faecalis
|
26.0
|
Erythromycin resistance
|
24
|
|
pSK41
|
Staphylococcus
aureus
|
46.4
|
Multidrug resistance
|
25
|
|
pBM4000
|
Bacillus
megaterium
|
53.0
|
rRNA operon
|
13
|
|
pI258
|
Staphylococcus
aureus
|
28.0
|
Metal ion resistance
|
26
|
|
pSLT
|
Salmonella
enterica ssp.
|
93.9
|
Virulence determinants
|
27
|
|
|
typhimurium
|
|
|
|
|
pMT1
|
Yersinia
pestis
|
101.0
|
Virulence determinants
|
28
|
|
pADP-1
|
Pseudomonas sp.
|
108.8
|
Atrazine (herbicide)
|
29
|
|
|
|
|
catabolism
|
|
|
pWW0
|
Pseudomonas
putida
|
117.0
|
Aromatic hydrocarbon
|
30
|
|
|
|
|
degradation
|
|
|
pBtoxis
|
Bacillus
thuringiensis ssp.
|
137.0
|
Mosquito larval toxicity
|
31
|
|
|
israelensis
|
|
|
|
|
pX01
|
Bacillus
anthracis
|
181.7
|
Exotoxin production
|
32
|
|
pSOL1
|
Clostridium
acetobutylicum
|
192.0
|
Solvent production
|
33
|
|
pSymB
|
Sinorhizobium
meliloti
|
1683.3
|
Multiple functions
|
34
|
Other plasmid-encoded traits also contribute
to the persistence of the host bacterium in otherwise inhospitable
environments. These include resistance to metal ions such as lead, mercuric,
and zinc (37), production of virulence factors that allow the
bacterium to colonize hosts and survive host defenses (38), and metabolic functions that allow utilization of
different nutrients. The last trait includes the plasmid-medi-ated biodegradation
of a variety of toxic substances such as toluene and other organic
hydrocarbons, herbicides, and pesticides (39). The production of plasmid-encoded bacteriocins to which
other microorganisms are susceptible can give the plasmid-containing bacterium
a competitive edge over other microorganisms in an ecological niche (39a), as can plasmid-located genes for bacteriophage
resistance and for the restriction of foreign nucleic acids which enter the
cell. Conversely, plasmid-encoded antirestriction systems may protect plasmid
DNA from degradation by host restriction enzymes when it first enters a new
cell (39b). The profound effects that plasmids can exert on
bacterial behavior is sharply illustrated by the recent observation that Bacillus cereus, an opportunistic food-borne pathogen; Bacillus thuringiensis, a source of commercially useful insecticidal proteins;
and Bacillus
anthracis, the causative
agent of anthrax, are mainly discriminated by their plasmids (40).
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