Kinetic Studies of Biodegradation

Kinetic Studies of Biodegradation

• Thousands of manufactured chemicals and materials are used, their ultimate fate in the environment often unknown
• These substances are discharged into the environment through air, water, or land
• Solid waste disposal is a significant environmental problem
• Many substances degrade slowly, harming plants and animals
• Biodegradation, aerobic or anaerobic, breaks down large molecules into smaller ones
• Biodegradation can be used to mitigate pollution and produce biogas
• Agricultural waste and organic matter are significant renewable energy sources
• Untreated animal manure is a major pollutant of air and water

Mechanisms of Biodegradation

• Cellulose, lignocellulose, and lignin are major plant biomass sources, polymeric substances crucial for the carbon cycle
• These polymers are degraded by various microorganisms producing enzymes
• Fungal and bacterial degradation can occur extracellularly
• Hydrolytic enzymes are responsible for cellulose and hemicellulose degradation
• Oxidative ligninolytic enzymes depolymerize lignin
• Many chemicals require different microorganisms and enzymes for degradation
• Growth-associated degradation uses organic compounds for carbon and energy, leading to complete mineralization. Archaea, prokaryotes, and eukaryotes play a role
• Co-metabolism involves metabolism of an organic compound alongside a growth substrate. Final products are often CO2 and methane
• Growth-associated degradation of aliphatic compounds produces CO2, H2O, and cell biomass

Growth-Associated Degradation of Aliphatic Compounds

• Cell biomass acts as biocatalysts for degradation
• Contaminated areas ultimately mineralize cell biomass
• Aromatic hydrocarbons (benzene, toluene, ethylbenzene, xylenes, naphthalene) are important industrial chemicals and fuels
• Phenols and chlorophenols are used in various industries

Growth-Associated Degradation of Aromatic Compounds

• Many microorganisms utilize catabolic pathways to degrade aromatic compounds
• Benzene oxidation begins by hydroxylation catalyzed by dioxygenase, leading to a diol converted into catechol by a dehydrogenase
• Monooxygenase and dioxygenase reactions are important mechanism steps
• Hydroxylation, oxygenolytic ring cleavage, isomerization and hydrolysis are common reactions for degrading aromatic substrates
• Bacteria with induced enzyme activity can adapt to diverse substrate mixtures and high degradation rates

Co-metabolic Degradation of Organopollutants

• Co-metabolism is an important aspect of microbial transformation
• Microorganisms that grow on one substrate can also oxidize another
• Co-substrates are not incorporated; however, their metabolites can serve as a substrate for other organisms in mixed cultures
• Enzymes and cofactors are involved in co-metabolic transformations
• Oxygenases and other enzymes are necessary for the conversion of organic compounds to natural intermediates like catechol and protocatechuate

Aerobic Biodegradation

• Many microorganisms grow in aerobic conditions using cellular respiration (CSP)
• Glucose is degraded into smaller molecules in the cytoplasm, which then enter mitochondria for aerobic respiration
• Oxygen is crucial for breaking down molecules into water and carbon dioxide
• Aerobic biodegradation is characterized by oxidation reactions, often catalyzed by oxygenases and peroxidases

Anaerobic Biodegradation

• Anaerobic biodegradation occurs in the absence of oxygen and various microbes have different roles
• Electrons originate from the oxidation of organic matter
• Manganese, iron, sulfur, sulfate, nitrate, and carbon dioxide are important electron acceptors
• Biogas generation from anaerobic digestion of organic matter is an effective and important renewable energy source
• Hydrolysis, acidogenesis, acetogenesis, and methanogenesis are the major steps of anaerobic digestion.
• These stages result in the production of methane and carbon dioxide

Biodegradation of Industrial Organic Pollutants

• The fate of industrial chemicals in the environment is important for designing biodegradation systems. Organic pollutants are toxic and accumulate in the environment.
• Petroleum hydrocarbons (PHCs) and chlorinated hydrocarbons (CHCs) are major pollutants
• PHCs degrade effectively under aerobic conditions
• CHCs degrade effectively under anaerobic conditions.

Biodegradation of Plastics

• Some plastics are resistant to biodegradation.
• Polycyclic aromatic hydrocarbons (PAHs) are toxic, mutagenic, and resistant to breakdown.
• Microbial communities and factors such as environmental conditions, nutrient levels, and temperature influence the rate and extent of plastic biodegradation
• Polyvinyl alcohol (PVA) is biodegradable, but this does not automatically mean it is bio-based.

The Pest Problem

• Pests damage crops, livestock, and property
• Pesticides are used to control pests, but they can have negative environmental and health consequences
• Biological pest control utilizes other organisms to manage pests. No chemical contamination, so no harm to the environment
• "Classical" biological control introduces natural predators, parasites, or pathogens of a target
• "Conservation" control enhances local natural enemies of the pest
• "Augmentation" control increases the number of existing pest enemies
• Biopesticides are produced from living organisms and are safer for humans than chemical pesticides
• Microbial pesticides, plant-incorporated protectants (PIPs), and biochemical pesticides are some types of biopesticides

Additional Notes (Categorized by Topic)

• Classifying pesticides: Pesticides are categorized by the organism they target (e.g., insects, weeds, rodents) or by their chemical structure (e.g., organophosphates, pyrethroids)
• Possible Health Effects: Pesticides have various effects on humans, with potential long-term or acute symptoms. Serious cases could lead to death.
• Integrated Pest Management (IPM): IPM uses a combination of techniques (natural methods, biological control, and, if absolutely necessary, pesticides) to minimize pest-related problems and environmental concerns.
• Disadvantages of biological pest control: Unforeseen population effects, potential new pest introduction from another region
• Biodegradation of petroleum hydrocarbons: PHCs degrade quickly aerobically. In contrast, Chlorinated hydrocarbons degrade slowly in anaerobic conditions.
• Biodegradation of aromatic hydrocarbons: Bacteria and fungi can utilize catabolic pathways.
• Biodegradation of plastics: Bio-based plastics are an alternative to traditional petro-based plastics, but not all bio-plastics are biodegradable.