Microbial break down

In order to minimize waste as well as to direct selectivity, a number of approaches toward dissipation-control are being examined. For example, both volatilization and photodecomposition often can be regulated to a desired degree by incorporation of a non-volatile resin additive into the pesticide formulation (35). The technique appears promising for insecticides, and there is no reason to believe it should not work for herbicides also. Another approach is inhibition of microbial break-down for example, N-methylcarbamate inhibitors of hydrolytic enzymes, such as PCMC ( -chlorophenyl N-methylcarbamate), applied together with a herbicide such as chloropropham [isopropyl N-(3-chlorophenyl)carbamate] which is inactivated by soil microbes, more than doubled the effectiveness (36,37). 

Pesticides vary widely in their chemical and physical characteristics and it is their solubility, mobility and rate of degradation which govern their potential to contaminate Controlled Waters. This, however, is not easy to predict under differing environmental conditions. Many modern pesticides are known to break down quickly in sunlight or in soil, but are more likely to persist if they reach groundwater because of reduced microbial activity, absence of light, and lower temperatures in the sub-surface zone. 

The second type of material includes spores, which may or may not produce disease symptoms but which can germinate in the insect gut and give rise to vegetative bacterial cells which in turn may produce, and exoenzymes such as phospholipases (lecithinases) or hyaluronidase. The phospholipases may produce direct toxic symptoms owing to their action on nervous or other phospholipid-containing tissue. Hyaluronidase breaks down hyaluronic acid and produces effects on animal tissue which are morphologically similar to the breakdown of insect gut wall in the presence of microbial insecticide preparations. 

A further application of the manipulation of microbial activity in the rhizo-sphere is their potential to remediate contaminated land. Bioremediation involves the u.se of microorganisms that break down contaminants. Radwan et al. (255) found that the soil associated with the roots of plants grown in soil heavily contaminated with oil in Kuwait was free of oil residues, presumably as a result of the ability of the resident rhizosphere microflora to degrade hydrocarbons. The use of plants as a means to accumulate pollutants such as heavy metals (256,257) to degrade hydrocarbons and pesticides (255) is already widely implemented and has proven to be successful. In some cases, there is no doubt that it is the plant itself that is responsible for the removal of the contaminants. However, in most... 

Mixed stands support more diverse microbial communities (promoting potentially more complete rhizodegradation by further breaking down byproducts). 

Endogenous microbial enzymes are sometimes utilized to break down their parent cells, and thus extract valuable intracellular materials. For instance, in the production of yeast extract, cells are allowed to autolyse at about pH 5 and 55 0. Proteases are probably the most important class of enzymes involved in autolysis, although others such as glucanases, lipases and nucleases also have... 

Biodegradability - Metabolix PHA offer hydrolytic stability under normal service conditions but when exposed to microbial organisms naturally present they break down enzymatically in soil, composting, waste treatment processes, river water and marine environments. They also rapidly decompose to carbon dioxide and water and will degrade in anaerobic environments, unlike some other biodegradable polymers. 

Microbial degradation of biocides has been described by Hugo [72] who points out that soil organisms are able to break down substances such as phenols added as fumigants. He also reviewed the utilization by bacteria of aromatic compounds (including the preservatives cresol, phenol, benzoic acid and esters of 4-hydroxybenzoic acid). Several types of preservatives and disinfectants, such as the QACs (e.g. cetrimide, cetylpyridinium chloride, benzalkonium chloride), chlorhexidine and phenylethanol can also be inactivated. Significantly, this only occurs at concentrations well below inhibitory or in-use concentrations [33] and thus cannot be responsible for insusceptibility. A further comment about chlorhexidine is given below. 

Aspartame is the most widely used artificial sweetener in the world. It was approved by the FDA for use in the USA in 1981, and now is approved for use in several other countries of the world. One of the drawbacks of aspartame is its instability to heat and acid. Under acidic conditions aspartame slowly hydrolyzes leading to a loss of sweetness, chemical interaction, and microbial degradation. The shelf life of the aspartame-sweetened products with high water content is limited to about 6 months, after which it breaks down into its constituent components and loses its sweetening abilities. At elevated temperatures, solid aspartame slowly releases methanol to form aspartyl phenylalamine and the dioxopiperazine. This reaction is especially favored at neutral and alkaline pH values. Because of this reason, aspartame cannot be used in hot baking foods. 

Carbofuran is soluble in water and moderately persistent in soil (half-life 30-120 days). Carbofuran is degraded by chemical, photochemical, and microbial processes. Hydrolysis is more rapid in alkaline conditions. Carbofuran breaks down in sunlight. Carbofuran has a high potential for leaching into groundwater. Carbofuran is mobile in sandy loam, silty clay, and silty loam soils. In surface water, carbofuran is subject to hydrolysis, particularly under alkaline conditions. Hydrolysis of carbofuran (half-lives) in water is 690, 8, and 1 weeks at pH values of 6, 7, and 8, respectively. As in soils, photodegradation and microbial transformation may also contribute to degradation. Carbofuran is not volatile and does not adsorb to sediment or particles. 

Molecules which can break down or permeabi-lize microbial membranes and thereby mediate extracellular killing of microorganisms, e.g. enzymes (lysozyme or cathepsin G), bactericidal reactive oxygen species and cationic proteins. 

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