Microbes and Organic Pollutants PDF

Microbes and Organic Pollutants Environmental Microbiology Environmental laws Superfund act (Comprehensive Environmental Response, Compensation and Liability Act – CERCLA) passed...

Microbes and Organic Pollutants Environmental Microbiology Environmental laws Superfund act (Comprehensive Environmental Response, Compensation and Liability Act – CERCLA) passed in 1986 Goal to investigate and clean hazardous substances in the environment by (1) removal actions for immediate threads (2) remedial actions to cleanup “Superfund Site” Inventory As of Sept. 2024, 1340 sites  More about Superfund Assessed for National Priority List and if deemed require immediate action, then stays on NPL Biological remediation can be economical compared to traditional removal or chemical approaches! The Process of Biodegradation Definition: The breakdown of organic contaminants that occur due to microbial activity Organic contaminants, due to their use as a food source, are substrates Is a pathway that leads to oxidation or breakdown of compound of concern Biodegradation Complete biodegradation is referred to as mineralization and with end products of CO2 + H20 Enzymes catalyze breakdown Biotransformation stops if any enzyme is not present or malfunctions Common for pollutants that require specialized enzymes and differ from natural substances Co-metabolism Incomplete biodegradation wehre partial oxidation of a substrate occurs but energy derived is not used to support microbial growth Occurs when organisms possess one ore more enzymes that can degrade a particular contaminant in addition to its target substrate therefore enzymes are non-specific Known to occur for TCE (trichloroethene) by methanotrophic bacteria  The maximum level of microbial activity expected under existing environmental conditions Influenced by several factors: Low microbial numbers Carrying Insufficient oxygen or nutrients Capacity Suboptimal temperature Low water content Contaminant properties will impact microbial biodegradation potential Genetic Potential and Adaptation Biodegradation occurs after microbial communities' acclimate to contaminant presence Previous exposure through repeated application will maintain a contaminants biodegradation pathway First time exposure will require an adaptation by mutating or gene transfer for biodeg. to occur But some are toxic! Bioavailability Compounds that are hydrophobic or sorbed to soils are not bioavailable Microbes take up compounds in aqueous phase Three modes of microbial uptake of liquid organics: (1) Utilization of soluble compound (2) Direct cell contact with compound (3) Direct contact with fine or submicrometer sized droplets dispersed in aqueous phase  Biosurfactants Three modes of microbial uptake of liquid organics: (1) Utilization of soluble compound (A) (2) Direct cell contact with compound (B) (3) Direct contact with fine or submicrometer sized droplets dispersed in aqueous phase (C) (4) Biosurfactants can increase solubility or facilitate attachment of microbial cells by making cell surface more hydrophobic (D) Example: trehalolipds Bioavailability and Soil Sorption Weakly bound or labile compounds are reversible and become available when released back into aqueous phase May diffuse into microsites in soil which are inaccessible Increased time in soil will decrease bioavailablity and biodegradation potential Contaminant Structure Steric Effects Branching or functional group will change chemistry of degradation reaction sites Electronic Effects Electron density changes at reaction sites; greater densities increase rates, lower densities reduce rates Contaminant Structure Steric Effects Branching or functional group will change chemistry of degradation reaction sites Electronic Effects Electron density changes at reaction sites; greater densities increase rates, lower densities reduce rates  Redox Conditions Organic Matter Content Environmen Nitrogen tal Factors which affect Temperature Biodegradat pH ion Salinity Water Activity Redox Conditions How much redox can happen – is oxygen present? Aerobic biodegradation much greater than anaerobic Alkane degradation only occurs in present of oxygen Some compounds can only be degraded anaerobically Chlorinated Organic Matter Content Greater OM  Greater number of microbes Low microbial biomass reduces genetic potential for biodegradation due to less species present Microbes in low biomass areas commonly dormant  Many organic pollutants are C and H rich leaving microbes N starved Utilization of C-containing contaminants increases Nitrogen demand for essential nutrients Adding N fertilizer will increase biodegradation rates Pollutant Sources Solvents, acids, bases, metals produced from paper, transportation, electronics, defense and metal industries Coal, natural gas, nuclear waste Pesticides Important Chemistry Definitions Functional group: atoms bonded in an arrangement that provides a compound its physical and chemical properties Rings: one or more atoms connected to form a ring (usually carbon- based) Unsaturated vs Saturated: the presence of double covalent bonds (single bonds = saturated, double bonds = unsaturated) Methyl groups: one carbon atom bonded to three H atoms morphine Pollutant types Aliphatics Alicyclics Aromatics Dioxins and PCBs Pesticides Aliphatics - Alkanes Alkanes are easy to degrade due to chemical structure Monooxygenase enzyme and dioxygenase enzyme to form fatty acids Fatty acids catabolized via Beta- Oxidation pathway Midsize straight- chain alkanes preferred by microbes Aliphatics – Alkanes Biodegradability is poor with branching in hydrocarbon chains Poor biodegradation in anaerobic conditions These are persistent in underground reservoirs Aliphatics – Halogenated Aliphatics Replaces a hydrogen with a halogen group (fluorine, chlorine, bromine) Chlorinated solvents are very common but more slowly degraded as the chlorine inhibits degradation aerobically due to reduced electron densities Dioxins Created during waste incineration, smoke stack release Well known example: TCDD Once thought to be highly carcinogenic, but still toxic by changing behavior and neurology Can be biodegraded but very minimal (low water solubility) Dioxins Bacterial and fungal biodegradation has been shown but is minimal One study (Phillippi et al., 1982) showed less than 1% of the original dioxin was degraded over a 12 week period PCBs Polychlorinated biphenyls (PCBs) are chlorine-substituted biphenyls Used as heat-resistant oils in heat transfer, hydraulic fluids and lubricants, plasticizers in food packaging materials, petroleum additives Accumulation in environment has occurred partially due to low biodegradation potential due to the Cl PCBs PCBs have low bioavailability because of the chlorinated component However, anaerobic- aerobic sequential process may remove the chlorine and then allow for mineralization of no to low-C residues Kaleem et al. 2022  Bioremediation Goal: exploit naturally occurring biodegradation processes to clean up contaminated sites In situ: in-place Ex situ: outside of place of contamination Biostimulation: changing conditions to enhance biodegradation Intrinsic bioremediation represents the indigenous level of biodegradation that occurs without biostimulation https://www.youtube.com/watch?v=bAwAFu7Mrk4 Variables important for Bioremediation Lab studies used to understand if biodegradation can occur; if not, is there a limiting factor in the environment? Oxygen Nutrients Surfactants Microbe Additions In situ bioremediation In-place biodegradation in the vadose zone and groundwater with nutrients and oxygen pumped into contaminated area to promote the in-place breakdown Ex-situ treatment pumps the contaminated water and placed in a bioreactor for breakdown  Bioremediation in groundwater by air sparging Air sparging used to deliver oxygen to saturated Oxygen and zones Methane can be added to cometabolize Nutrients chlorinated solvents through the activity of methane monooxygenase Microbial Injection/Additions When biodegrading organisms are not present Bioaugmentation: introducing microbes with biodegradation capability to augment existing communities Can use genetically- engineered organisms made in lab Often does not work in the field: there is no niche for them (outcompeted by existing microbes), delivery to contaminated site is difficult as they sorb to soils