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