Bioremediation
• Use of bacteria to clean up (detoxify) pollution
• Contained wastes (in a factory, in tanks)
• Contaminated sites
•soil
•Water
• Other technologies also available
VERY EXPENSIVE
Tanks at Hanford
Bioremediation as Part of All Remediation
Technologies
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Biodegradable Contaminants
• Bacteria have the natural ability to either grow on toxic
compounds or convert them to nontoxic products
• Classes of contaminants biodegraded
– Aromatics (toluene, xylene, benzene, phenol, naphthalene)
– Chlorinated aromatics (chlorobenzene, PCBs)
– Chlorinated solvents (chloroform, trichloroethylene [TCE])
These mostly involve enzymes called oxygenases
– Toxic metals (mercury)
– Other toxic metals can be taken up or precipitated by cells
• Cu, Co, Ni, Pb
• Not detoxified but can be removed more easily
Bioremediated Contaminants
Toluene degradation
T2MO
T3MO
TCE degradation
TOD
sMMO
T2MO
T2MO
TOD
T3MO
toluene-cisdihydrodiol
dehydrogenase
3-methylcatechol
catechol-2,3
dehydrogenase
TCE epoxide
glyoxylate formate
chloral hydrate
(not in whole cells)
sMMO
T2MO
(only with sMMO)
dichloroacetate
glyoxylate formate
The University of Minnesota Biocatalysis/Biodegradation Database, http://umbbd.ahc.umn.edu/
•Organisms that contain these oxygenases will detoxify
toluene, TCE, and many other aromatic and chlorinated toxic
compounds
How Does Contamination Occur?
Spills or leaks sink into soil or water
Get transported by water movement
Contaminants get Dispersed
Plumes of Contaminants Remain
Plumes of Contaminants Remain
Natural Bioremediation
Problem: how to get bacteria to contaminant?
• Natural strains have biodegradative capability
• Can use in situ populations
• Need to increase total population by adding substrates
• Contaminated sites often very low nutrient
• Contain mixed populations of bacteria
•Gram of soil can contain 109 bacteria
•1000s of types (tremendous diversity)
• Stimulate specific types with specific nutrients
•Example: bacteria that grow on methane
accidentally detoxify TCE
add methane ---> population increases -->get
degradation of TCE
• Oil spills: just need to add a N and P source
What is Role for Engineering
Bacteria?
• Increase substrates detoxified
– More individual compounds detoxified by one strain
– Simultaneous detoxification
• Increase rate of detoxification
– Increase expression
• Increase access to hydrophobic contaminants
– If contaminant can be accessed, it will not persist
– Hydrophobic contaminants persist
Access to Contaminants
No surfactants
With surfactants
Add genes to synthesize surfactants
Problems with Genetically
Engineered Microorganisms (GEMs)
• Don’t survive in the environment
– Can’t compete with existing bacteria
• Cloning in survival or persistence genes
raises regulatory issues
• Few field trials of GEMs, identified
strains that can persist
• Greatest potential of GEMs for
bioremediation is contained waste