Microbial influenced degradation

Knight, J., Cheeseman, C. and Rogers, R. (1999) Microbial influenced degradation of solidified wastes, in J. Mehu et al. (Eds.), Waste Stabilization and Environment 99, Villeurbanne, France, 13-16 April 1999, Proceedings of conference presentation, Soci ti alpine de publications, Grenoble, France, pp. 143-148. 

Rogers et al. put it an understanding of concrete degradation may be incomplete without including the effects of microbial influenced degradation, or briefly. 

Corrosion, and thus MIC, is used to address degradation in metals. We will use the term microbial influenced degradation , or briefly MID, to address degradation of non-metallics. 

Knight J, Cheeseman C, Rogers R (2002) Microbial influenced degradation of solidified waste binder. Waste Management (22) 187-193... 

Moisture strongly influences degradation. Substances that need anaerobic conditions will be more easily degraded at very high soil moisture because increased water combined with microbial activity will remove oxygen. An intermediate amount of moisture will stimulate aerobic microbial growth. 

The choice of the appropriate material is decisive for resistance against microbially influenced corrosion. This means that before the choice of material can be made, what kind of impacts is has to resist needs to be considered. Microbial influencing factors must also be considered. Accordingly, in the presence of volatile sulfur compounds, e.g., in sewage pipelines, it is recommended not to use materials like unprotected concrete which may be destroyed by the end product of the microbial degradation process (in this case, sulfuric acid formed by Thiobacilli). Another example would be the choice of a stainless steel or of an alloy that cannot be attacked under the conditions of a biofllm and the complex metabolic processes occurring underneath it. If, for instance, a material has to be chosen for static reasons, this material has to be protected by a coating or a liner made of an inert material. All these examples are based on the consideration that all attack factors have been identified by a complete inventory. 

Degradation or Transformation. Degradation or transformation of a herbicide by soil microbes or by abiotic means has a significant influence not only on the herbicide s fate in the environment but also on the compound s efficacy. Herbicides that are readily degraded by soil microbes or other means may have a reduced environmental impact but may not be efficacious. Consider the phenomenon of herbicide-resistant soils. In these cases, repeated application of a given herbicide has led to a microbial population with an enhanced ability to degrade that herbicide (252,253). This results in a decrease or total loss of the ability of the herbicide to control the weed species in question in a cost-effective manner. 

Sugai SF, JE Limndstrom, JF Braddock (1997) Environmental influences on the microbial degradation of Exxon Valdez oil on the shorelines of Prince William Sound, Alaska. Environ Sci Technol 31 1564-1572. 

Riis, V., Babel, W., and Pucci, O., Influence of heavy metals on the microbial degradation of diesel fuel, Chemosphere, 49 (6), 559-568, 2002. 

Middeldorp PJM, De Wolf J, Zehnder AJB, Schraa G (1997) Enrichment and properties of a 1,2,4-trichlorobenzene-dechlorinating methanogenic microbial consortium. Appl Environ Microbiol 63 1225-1229 Miller ME, Alexander M (1991) Kinetics of bacterial degradation of benzylamine in a montmorillonite suspension. Environ Sci Technol 25 240-245 Montville R, Schaffner DW (2003) Inoculum size influences bacterial cross contamination between surfaces. Appl Environ Microbiol 69 7188-7193 Mortland, MM (1970) Clay-organic complexes and interactions. Advances in Agronomy 22 75-117... 

Bioavailability is also influenced by certain, albeit poorly understood, characteristics of bacteria. To degrade soil-sorbed molecules, bacteria must either use sorbed molecule directly or facilitate desorption in some manner. Mechanisms underlying the apparent availability of sorbed chemicals are complex due to the divergent properties of chemicals considered, the resultant sorption/desorption mechanisms, the metabolic diversity of microorganisms, and the heterogeneity of soils. Several microbial-based mechanisms have been proposed for the access of soil-sorbed organic chemicals (i) production of bio surfactants (Desai and Banat 1997 Alexander 1999) ... 

Redox mediators, such as flavins or quinones, are usually involved in the azo bond reduction. Therefore, the azo bond cleavage is a chemical, unspecific reaction that can occur inside or outside the cell, relying on the redox potential of the redox mediators and of the azo compounds. Also the reduction of the redox mediators can be both a chemical and an enzymatic process. As a consequence, it is an evidence that environmental conditions can affect the azo dyes degradation process extent both directly, depending on the reductive or oxidative status of the environment, and indirectly, influencing the microbial metabolism. 

During the wastewater treatment, an oxidative conversion of the surfactant molecules leads predominantly to the formation of polar compounds. They display a particularly high solubility and mobility in the aqueous medium and, therefore, transportation over relatively long distances can occur if they are not further degraded, resulting in the wide dissemination of these pollutants in riverine systems and thus also to estuaries, coastal regions and ultimately the marine environment (see Chapters 6.2 and 6.3). In the latter, the final levels will mainly be influenced by dilution effects and physical removal by precipitation or adsorption [63] because of relatively low microbial activity in this ecosystem compared with fresh water environments [64]. 

Once the indigenous community of microorganisms has become acclimated to the degradation of a chemical at an interface and the activity becomes marked, the community may retain its active state for some time. Too little information is presently available to permit generalizations to be made among compounds regarding the duration of the beneficial influence of prior additions of the compound. It is presently not clear why a microbial community which has acclimated to a particular substrate loses that activity. This could be a result of the decline in numbers or biomass of the responsible microorganisms or a loss of the metabolic activity in the absence of the specific compound. 

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