-Teen Biotech Challenge-
Bioremediation
Microbial Bioremediation
Process
Microorganisms utilize electron acceptors like oxygen, nitrate, iron(III), sulfate, and carbon dioxide to transfer the electron from contaminant and gain energy while reducing the toxic contaminant into a less toxic substance. (4.10)
To break down contaminants, microbes utilize oxidation or the transfer of electrons from an electron donor. In oxidation, microbes transfer the electron to oxygen, nitrate or iron through oxidoreductases enzyme that cleave chemical bonds and promote the oxidation process. Eventually, the contaminant compound becomes a harmless one while microbes gain energy through the transfer of electron that creates a proton gradient as electrons pass the electron transport chain and stimulate an enzyme to generate ATP molecules. Microbes use heavy metals for enzymatic catalysis, nutrient transport, protein structure, charge neutralization, and control of osmotic pressure. Heavy metals also aid enzymes concerned in the a variety of metabolic pathways. Microbes use intermolecular forces to bind metal cations to negatively charged groups in cell walls. Redox reaction occurs and precipitants are formed where the level of toxicity is reduced. In addition, microbes need energy and carbon to survive, in which case, the degradation of organic contaminants provide the requirements of life for microbes. (4.9, 4.35, 4.36)
Enzymes used:
Oxygenases uses oxidation by utilizing FAD, NADH, NADPH as a cosubstrate which transport electrons to oxygen molecules. Oxygen is needed by oxygenases to cleave aromatic rings (ring structure formed by 6 carbon atoms, each attached to a single hydrogen atom with alternating pi bonds) or increase water solubility of substance for metabolism of the organic contaminant to occur. Why is oxygen used? Oxygen has a strong electronegativity pull, therefore it is easier to accept electrons. Therefore, oxygenases are mostly used for the dehalogenation of halogenated methane, ethylenes, and ethanes. (4.9, 4.35, 4.36)
Laccases are enzymes which use oxidation to catalyze ortho, paradiphenols, aminophenoles, polyphenols, polyamines, lignings, and aryl diamines.
Below is the general reaction mechanism for phenol (corrosive chemical that burns the skin found in airfreshener and other cleaning agents) oxidation by laccase - Karigar, Chandrakant
Hydrolases obstruct the crucial chemical bonds found in toxic molecules through hydrolysis. Hydrolysis is the usage of water to seperate ions in a substance and therefore breaking the bond within a molecule.
Below is the Proposed mechanism for the hydrolysis of cellulose by the fungal cellulase enzyme system - Karigar, Chandrakant
Lipases reduce hydrocarbon amounts from contaminated sites by a variety of reactions including hydrolysis, interesterification, esterification, alcoholysis, and aminolysis. These enzymes break down chains of lipids like triacylglycerols into fatty acids. Therefore, oil spills remediation employ lipases to break down the oil.
The image below represents the proposed mechanism for triolein hydrolysis by Candida rugosa lipase in biphasic oil-water system. CE represents the enzyme concentration in the bulk of the water phase - Karigar, Chandrakant
Peroxidases consumes hydrogen peroxide to oxidize lignin and other phenolic compounds. This enzyme is critical to life because in plants, it contribute to metabolic processes of auxin, cross-link of cell wall, and pathogenic defense system while in animals, it contributes to the regulation of hormones and immune system responses.
The figure below displays the lignin peroxidase catalyed oxidation of nonphenolic lignin model compound - Karigar, Chandrakant
Requirements