Microbial populations

Environmental impact studies on NE have been performed. Although undiluted NE inhibits seed growth, no effect on plant growth was observed when exposed to 6, 000 ppm-min of NE and only minor effects were observed at the 60, 000 ppm-min exposure level (41). Exposure of microbial populations to 25% NE in air for seven hours showed normal growth. NE is not an o2one-depleting gas (20). 

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. 

Favorable polymer physical properties include water solubiUty and sample purity. Environmental conditions to consider in evaluating biodegradabihty are temperature, pH, moisture, oxygen, nutrients, suitable microbial population (fungal, algae, bacterial), concentration, and test duration. 

Agronomic Properties and Nutrient Release Mechanisms. The mechanism of nutrient release from SCU is by water penetration through micropores and imperfections, ie, cracks or incomplete sulfur coverage, ia the coating. This is followed by a rapid release of the dissolved urea from the core of the particle. When wax sealants are used, a dual release mechanism is created. Microbes ia the soil environment must attack the sealant to reveal the imperfections ia the sulfur coating. Because microbial populations vary with temperature, the release properties of wax-sealed SCUs are also temperature dependent. 

The addition of therapeutic or cosmetic agents to dentifrices has paralleled advances in knowledge about factors affecting the human dentition. Agents added to dentifrices can act directly on the host tooth stmcture or on specific oral accumulations, for example, the principal action of fluoride is on the tooth enamel. The primary action of an abrasive, however, is on an accumulated stained pellicle. Oral accumulations of interest to preventive dentistry are dental pellicles, dental plaque, dental calculus (tartar), microbial populations responsible for oral malodor, and oral debris (food residues, leukocytes, etc). Plaque is most important because of its potential to do harm. 

As predicted by the Arrhenius equation (Sec. 4), a plot of microbial death rate versus the reciprocal or the temperature is usually linear with a slope that is a measure of the susceptibility of microorganisms to heat. Correlations other than the Arrhenius equation are used, particularly in the food processing industry. A common temperature relationship of the thermal resistance is decimal reduction time (DRT), defined as the time required to reduce the microbial population by one-tenth. Over short temperature internals (e.g., 5.5°C) DRT is useful, but extrapolation over a wide temperature internal gives serious errors. 

Viable count Measurement of the concentration of live cells in a microbial population. 

Activated sludge Material containing a very large active microbial population used in the purification of waste water. 

You have now demonstrated the capability of exponentially increasing microbial populations to rapidly produce protein. However, although such outputs of protein are possible in theory, they cannot be achieved in practice, since exponential growth cannot be maintained for such periods because bioreactors are limited in size. 

Cellulose in the wastewater stream is not generated but it is consumed and biomass produced by the microbial population as a substrate for energy. 

It is only very recently that organic componnds synthesized by humans have begun to exert a selection pressure upon natural populations, with the consequent emergence of resistant strains. Pesticides are a prime example and will be the principal subject of the present section. It should be mentioned, however, that other types of biocides (e.g., antibiotics and disinfectants) can produce a similar response in microbial populations that are exposed to them. 

Pharmaceutical products are used in a variety of ways in the prevention, treatment and diagnosis of disease, hi recent years, manufacturers of pharmaceuticals have improved the quality of non-sterile products such that today the majority contain only a minimal microbial population. Nevertheless, a few rogue products with an unacceptable level and type of contamination will occasionally escape the quality control net and when used may, ironically, contribute to the spread of disease in patients. 

The indigenous microbial population is quite different in the home and in hospitals. Pathogenic organisms are found much more frequently in the latter and consequently are isolated more often from medicines used in hospital. Usually, there are fewer opportunities for contamination in the home, as patients are generally issued with individual supplies in small quantities. 

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