esm222_17_biodegradation - ESM 222 Biological Degradation Biodegradation involves the transformation of organic pollutants enzyme-catalyzed reactions

1 © Arturo A. Keller ESM 222 Biological Degradation 2 © Arturo A. Keller Biological Degradation Biodegradation involves the transformation of organic pollutants enzyme-catalyzed reactions Inorganic pollutants (e.g. Fe 2+ , Pb 2+ , NO 3- , NH 4+ ) may also be used by microorganisms and plants for oxidation/reduction reaction generally do not remove inorganic pollutant from environment 3 © Arturo A. Keller Biological Degradation Biological transformations Can accelerate by several orders of magnitude the rate of transformation of a pollutant Enzymes lower the activation energy required for a reaction Provide a surface where pollutant and oxidant can meet 4 © Arturo A. Keller Biological Degradation 5 © Arturo A. Keller Biological Degradation The organic pollutant may be degraded as a substrate (i.e. a good food source), usually as a carbon source via cometabolism (i.e. the bugs generally prefer something else but have the enzymes to partially degrade the pollutant) 6 © Arturo A. Keller Biological Degradation

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7 © Arturo A. Keller Biological Degradation A major issue in biodegradation is “bioavailability”: Is the pollutant available to the microorganisms for degradation? Is it dissolved? Can they use a sorbed pollutant? 8 © Arturo A. Keller Biological Degradation 9 © Arturo A. Keller Biological Degradation Microbes have enzymes inside and outside (exoenzymes) of the cell wall Not all microbes carry the necessary enzymes for degradation of all pollutants Pollutants with unusual chemical structures will not be easily degraded 10 © Arturo A. Keller Biological Degradation 11 © Arturo A. Keller Biological Degradation Some enzymes are very specific to a particular chemical and do not serve to degrade/transform other molecules Other enzymes are non-specific and result in the “chance” transformation of pollutants - this is the explanation for cometabolism 12 © Arturo A. Keller Biological Degradation Example: degradation of TCE Methanothrops (methane eaters) have an enzyme, denominated Methane Monooxygenase (MMO), which is quite non-specific MMO is also used by bacteria to degrade most hydrocarbons

13 © Arturo A. Keller Biological Degradation 14 © Arturo A. Keller Biological Degradation In general, one microorganisms will not be responsible for the complete degradation of the pollutant to CO 2 , H 2 0 (and Cl - , NH 4 + , etc.) Microorganisms cooperate to make the transformation, each one providing their enzymatic capabilities and making use of the carbon source 15 © Arturo A. Keller Biological Degradation Example of cooperative degradation: 16 © Arturo A. Keller Biological Degradation