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

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, Toluene degradation TCE degradation T2MO T3MO TOD toluene-cis- dihydrodiol dehydrogenase toluene-cis- dihydrodiol dehydrogenase catechol-2,3 dehydrogenase catechol-2,3 dehydrogenase 3-methylcatechol dichloroacetate glyoxylate formate TCE epoxide chloral hydrate (not in whole cells) sMMO T2MO TOD T2MO (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 water Get transported by water movement

Contaminants get Dispersed

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 10 9 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