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Ø TABLE 10-1 ^^ß



The rates of bacterial growth and death are greatly influenced by environmental parameters. Some envi­ronmental conditions favor rapid bacterial reproduc­tion, whereas others do not permit any bacterial growth. Not all bacteria can grow under identical conditions. Each bacterial species has a specific toler­ance range for specific environmental parameters. Outside the range of environmental conditions under which a given bacterium can reproduce, it may either survive in a relatively dormant state or may lose via­bility. Loss of viability means the loss of the ability to reproduce, which leads to death. The effects of envi­ronmental factors on bacterial growth and death rates can be seen as differences in rates of reproduc­tion or death of a culture under varying environmen­tal conditions.

It is a particular environmental parameter or in­teraction of environmental parameters that controls the rate of growth or death of a given bacterial species. Bacteria have particular physiological prop­erties that determine the conditions under which they can grow. In nature, conditions cannot be con­trolled and many species co-exist; fluctuating envi­ronmental conditions favor population shifts because of the varying growth rates of individual microbial populations within the community of a given loca­tion. In the laboratory it is possible to adjust condi­tions to achieve optimal growth rates for a given

microorganism. Many laboratory and industrial ap­plications use pure cultures of microorganisms. This facilitates the adjustment of the growth conditions so I that they favor optimal growth of the particular bac-1 terial species. Similarly, in industrial fermentors, I which are large growth chambers (often thousands of liters) used to grow bacterial cultures, conditions can be adjusted to optimize bacterial growth rates, thereby maximizing the production of desired bacte­rial metabolic products.



Temperature is one of the most important factors af-1 fecting rates of microbial growth. The temperatures at which specific enzymes and cellular structures function varies from one microbial species to another, depending on the specific chemical compositions specified by the genome of the organism. The mini­mum and maximum temperatures at which a mi­croorganism can grow establish the temperature growth rangefor that microorganism (FIG. 10-11), I Within this growth range there will be an optimal growth temperature at which the highest rate of re­production occurs.

The temperature growth range is defined by the minimum and maximum temperatures at which a

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Date: 2015-02-28; view: 1212

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