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Bioremediation• Use of bacteria to clean up (detoxify) pollution
• Contained wastes (in a factory, in tanks)• Contaminated sites
•soil•Water
• Other technologies also availableVERY EXPENSIVE
Tanks at Hanford
Bioremediation as Part of All Remediation Technologies
http:/ / www.clu- in.org/ products/ asr/ section3.html
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
The University of Minnesota Biocatalysis/Biodegradation Database, http://umbbd.ahc.umn.edu/
Toluene degradation TCE degradation
T2MOT2MO
T2MOT2MO
T3MOT3MO
T3MOT3MO
TODTOD
toluene-cis-dihydrodiol
dehydrogenase
toluene-cis-dihydrodiol
dehydrogenase
catechol-2,3dehydrogenase
catechol-2,3dehydrogenase
3-methylcatechol
dichloroacetate glyoxylate formate
glyoxylate formateTCE epoxidechloral hydrate
(not in whole cells)
sMMOsMMO
sMMOsMMO
T2MOT2MO TODTOD
T2MOT2MO
(only with sMMO)
•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 waterGet transported by water movement
Contaminants get Dispersed
Plumes of Contaminants Remain
Plumes of Contaminants Remain
Natural BioremediationProblem: 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