Biological Warfare
Bacterial Toxins: Bacteriocins and Choleratoxin
Bacteriocin
Kill other closely-related non-toxic bacterial
E. coli produces colicins
Yersinia pestis makes pesticins
Usually encoded on plasmid - e.g. ColE plasmids in E. coli
ColE1 plasmid-encoded gene codes for protein that inserts through membrane of target E. coli and creates a membrane pore through which cell contents leak out
ColE2 and ColE3 plasmids have genes that encode nucleases
Colicin E2 is a DNase
Colicin E3 is an RNase that cuts 16S rRNA
How come toxin-producers aren't killed? Have immunity due to immunity proteins that are encoded on the same plasmid. Immunity proteins bind the active site of the colicin.
In a large bacterial population, one cell may produce large quantities of colicin then burst to release the colicin into the environment. Altruism? No, because advantageous to cells of the same strain because decreases competition for nutrients
Produced by Vibrio cholerae; causes cholera in humans that can be lethal due to diarrhea and dehydration
Causes overproduction of cAMP so intestinal cells lose water and ions
3 proteins - A1, A2 and B; A1 and A2 are linked together and 5 B subunits form a ring around A1/A2 structure
B protein recognizes and binds to a ganglioside in animal cell membrane. A1 is released into cell and binds to the regulatory unit, G-protein, of adenylate cyclase, the enzyme responsible for making cAMP. G-protein is then locked onto adenyl cyclase unit so cAMP is always made.
Contain kappa particles that are actually bacterial symbionts
K/k gene is located in nucleus of Paramecium
If Paramecium is KK or Kk, the symbiotic bacteria can grow and divide. If Paramecium is kk, loses the symbionts
Killer Paramecium release symbiotic bacteria into environment where they're swallowed by other Paramecium. If Paramecium doesn't contain kappa particles and swallows them, the bacteria (kappa particles) are digested and release a toxin called the R-body that is encoded by a defective virus existing as a plasmid in the symbionts. Paramecium with kappa particles are immune to the toxin.
Bacillus thuringiensis Insecticides
1) Insect larvae ingest Bacillus spores
2) Digestion of bacteria releases toxin crystals
3) Toxin crystals dissolve into pairs of pro-toxin molecules linked by disulfide bonds
4) Disulfide bonds are broken to free single pro-toxin molecules
5) Pro-toxin is converted to toxin in larval digestive system
6) Toxin inserts into cell membrane of cell walls of intestinal cells and forms a pore through which ATP and ions are lost
To improve for biological control:
1) Clone toxin gene behind constitutive promoter so toxin is produced even in non-spore forming cells
2) Clone several toxin genes (code for toxins that kill different insects) onto a single plasmid
3) Since Bacillus sprayed onto a field can't protect plant roots, clone the toxin genes into Pseudomonas (colonizes roots) and incorporate engineered bacteria into the soil
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Last updated: 1-May-06 / laa