23.microbe.biorem.10

23.microbe.biorem.10 - Microbial Bioremediation...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Microbial Bioremediation Introduction Types of Respiration Processes Some Types of Biodegradation Reactions Bioremediation Strategies Summary and Conclusions I. Introduction Most microbes live in soils and sediments. There is literally over a million species. To date less than 5% have been characterized. They use soil organic matter as their carbon source. II. Types of Respiration Processes Processes depend upon the terminal electron acceptors for respiration. Communities include those in the photic, oxic and anoxic zones. Redox potential determines viability of any e- acceptor. Aerobic (a) use O2 for respiration. Anaerobic (b) use other electron acceptors. Facultative (c) can grow either way ("switch hitters"). Microaerobic (d) need only a small amount of O2. Aerotolerant (e) anaerobic but can tolerate O2. Types of Microbes in the Environment Temperature and pH Influences Microbes generally have a temperature optimum at which metabolic rate is o maximal (15-45 C). While they best function at pH 5.5 8.5, some can tolerate extreme acidic (acidophiles) or basic (alkaliphiles) Optimal Growth Conditions Region 1: lag phase microbes are adjusting to new substrate (carbon source). Region 2: exponential growth phase microbes have acclimated to the new conditions. Region 3: stationary phase limited substrate or electron acceptor limits growth rate. Region 4: decay phase substrate supply is exhausted. III. Some Types of Biodegradation Reactions All substrates are not equally degraded. Reactions depend upon the functional groups present (inclusive of steric hindrance) and enzymes available. Some Definitions Catabolic reactions involve breakdown of complex organic structures and yield energy to the active microbes. Conversion of organic substrates to inorganic forms (i.e. CO2 and H2O) is referred to as mineralization. Substrates resistant to digestion referred to as recalcitrant. Cometabolism is where microbes survive on respiration of a primary substrate (carbon source) while they also degrade a secondary one (a contaminant at low levels). Monooxygenases (P450s) insert one O into a Natural Bioremediation to Digest Contaminants For millions of years natural oil seeps have occurred, with the oil ultimately degraded by natural microbial actions. A. Oxidation of Simple Hydrocarbons Alkanes oxidized to fatty acids by monooxygenases. Fatty acids then complex with coenzyme A (CoA). Fatty acid-CoA complex subjected to -oxidation. 2-Carbon acetyl CoA units cleaved off for insertion into the TCA cycle. Ultimately, ATP is Monooxygenases typically insert single O atoms into alkanes or aromatic hydrocarbons. Dioxygenases open the rings of catechols resulting from monooxygenation and hydrolysis. B. Oxidation of Aromatic Hydrocarbons Dioxygenation Results in Ring Cleavage Catechols produced by monooxygenases are subject to dioxygenation. Two pathways may be utilized, ortho or meta. Resultant products are again inserted into the TCA cycle. Again, ATP is generated. C. Degradation of Halogenated Substrates Halogenated solvents were once widely used by the electronics and dry cleaning industries. The cleaning solvent perchloroethylene is readily subjected to reductive dechlorination. The alkene can be reduced to ethane (anoxic), or mineralized in oxic D. Pesticide Degradation by Soil Microbes As an alkyl halide, the herbicide atrazine can be readily degraded. Reactions include hydrolysis and oxidative Ndealkylation. Ultimately, the products are mineralized by further oxidation. 2,4,5-T is a phenoxyacetic acid herbicide used to defoliate forests and jungles. It was also an active component of Agent Orange (50-50 mix of 2,4,5-T and 2,4-D). Subjected to oxidative dealkylation, hydrolytic dechlorination, and dioxygenation. Degradation of Halogenated Pesticides Degradation of Halogenated Pesticides Thiobencarb is an herbicide that when reductively dechlorinated by microbes becomes toxic to rice. E. Biomethylation of Metals Many soil microbes methylate metals (Hg, As, Pb, Se). Methylation is a reductive process. Methylated metals are more fat soluble bioaccumulative. Some top-level carnivorous fishes can be unsafe to regularly consume (salmon, halibut, swordfish, shark, etc.). Inorganic metals can be both oxidized or reduced via microbial actions, such as Cr3+ to Cr6+ and vice versa. IV. Bioremediation Strategies Aerobic digestion is used for phase 2 sewage treatment to degrade wastes and reduce BOD prior to release. Bioremediation the use of an organism to degrade toxic chemicals or other chemical wastes. Organisms include Basic Approaches Use of natural bacteria (intrinsic bioremediation) advantage is they tend to be adapted for the local environment; disadvantage is that they may degrade a waste into products that may be unknown and toxic. Use of cloned bacteria (enhanced bioremediation) advantage is that they can be selected based on the known non-toxic products they produce; disadvantage is that they might not be adapted for the local environment. Some Chemicals Subjected to Sewage normal treatment and in groundwater from sewer pipe or septic tank seepage. Crude oil in coastal estuaries and on beaches. Gasoline in groundwater from gas station storage tanks. TCE and other cleaning solvents in groundwater. Pesticides in sediments, such as DDT and atrazine. Bioremediation Intrinsic Bioremediation of TCE Use of Bioremediation on Crude Oil Most effective in estuarine environments where there is an abundance of micronutrients and microbes are plentiful and diverse. Summary and Conclusions Microbes use different forms of respiration for bioremediation processes aerobic is preferred. Microbial degradation is a natural process (intrinsic). Recalcitrant chemicals are resistant to degradation. Most wastes are ultimately subjected to mineralization. Bioremediation is the use of organisms to degrade wastes. Approaches include use of natural or cloned microbes. Bioremediation can be used for both surface and ...
View Full Document

This note was uploaded on 06/29/2011 for the course GENETICS 101 taught by Professor Debrakimbrell during the Summer '09 term at UC Davis.

Page1 / 23

23.microbe.biorem.10 - Microbial Bioremediation...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online