Bioremediation metabolic pathways

Rate-limiting factors for bioremediation can include a lack of sufficient organisms with the metabolic pathways required for degradation. Temperature, oxygen supply, contaminant availability, chemical structure of the contaminant, and soil chemistry can all effect aerobic biodegradation rates. Nutrients such as nitrogen and phosphorous are necessary for biodegradation. 

Understanding the metabolic, or degradation, pathways involved in the bioremediation of contaminants can be invaluable. For certain contaminants, only after the responsible pathway(s) is known can mineralization be considered a possibility. Metabolic pathways can provide critical information regarding the ... 

Cutright, T. Lee, S. Bioremediation of PAH contaminated soil microorganisms and metabolic pathways. Fresenius Environ. Bull. 1994, 3 (7), 413-421. 

Fungal metabolism of PAHs has been studied in different contexts (1) the analogy between the metabolic pathways used by fungi and by higher organisms (Smith and Rosazza 1983), (2) as a detoxification mechanism, and (3) due to interest in their use in bioremediation programs. 

Kotrba, P. and Ruml, T. (2000). Bioremediation of heavy metal pollution exploting constituents, metabolites and metabolic pathway of livings. 

Not all of the ACS program have been included in this book, which was edited by Jay J. Gan, Peter C. Zhu, Ann T. Lemley, and myself. Contributions from additional authors, who could not participate in the symposium but whose work contribute to an even more inclusive treatise, are included in this book. One particular contribution. Chapter 4 by Lawrence P. Wackett entitled Evolution of New Enz5nnes and Pathways Soil Microbes Adapt to 5-Triazine Herbicides is especially appropriate because it concerns our ability to respond to the environmental pollution problem. This chapter describes a Pseudomonas species as a model to understand how bacterial genes involved in the metabolism of anthropogenic chemicals may arise and spread in the environment. The author describes how the ability to metabolize Atrazine by a Pseudomonas species evolved by recruiting enzymes from the amido-hydrolase superfamily to form a metabolic pathway to efficiently metabolize 5-triazine herbicides. Examples of the bioremediation of Atrazine-contaminated soil are described by Edward Topp, et al. in Chapter 11. 

The capacity of Archaea to inhabit extreme habitats and their varied metabolic pathways may prove useful to society. For example, methane is a valuable source of energy and already its release from landfill sites is being harnessed in some countries to provide energy for domestic consumption. Other Archaea may be valuable for the bioremediation of polluted areas because they prefer highly acidic or highly alkaline media and several species degrade organic molecules such as polychloro biphenyls (PCBs) while others can extract heavy metals from waste materials. 

However, the many pathways by which MTBE and other oxygenates may be biodegraded anaerobically have been the subject of recent research and ongoing studies. Table 24.12 highlights the various electron acceptors that are used in anaerobic bioremediation studies and contrasts the products of complete anaerobic degradation with those for aerobic metabolism. 

In the selection of a microbial system and bioremediation method, some examination of the degradation pathway is necessary. At a minimum, the final degradation products must be tested for toxicity and other regulatory demands for closure. Recent advances in the study of microbial metabolism of xenobiotics have identified potentially toxic intermediate products (Singleton, 1994). A regulatory agency sets treatment objectives for site remediation, and process analysis must determine whether bioremediation can meet these site objectives. Specific treatment objectives for some individual compounds have been established. In other cases total petroleum hydrocarbons total benzene, toluene, ethyl benzene, and xylene (BTEX) or total polynuclear aromatics objectives are set, while in yet others, a toxicology risk assessment must be performed. 

Aerobic bacteria complete most of the petroleum bioremediation applications, particularly those above the groundwater table. Aerobes are those bacteria that require an oxygen source as their TEA. Conversely, anaerobic species require the absence of oxygen (anoxic conditions) for their respiration. In situ anaerobic bioremediation is typically only conducted in the saturated zone because of the difficulty in maintaining a strict anaerobic environment. In some instances, facultative anaerobes are utilized because they can alter the respiration to be metabolically active under both anaerobic and aerobic conditions. As such, the type of TEA available will dictate the metabolism and subsequent degradation mode. The most common TEAs used for bioremediation are listed in Table 2. Careful selection of microbe-TEA combinations can enable a specific degradation pathway to facilitate cometabolism and prevent undesired degradation by-products. 

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