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Factors That Encourage and Limit the Growth of Microorganisms

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Factors That Encourage and Limit the Growth of Microorganisms Medium In the laboratory, bacteria are normally grown (cultured) in either liquid medium in flasks, bottles or fermenters, or solid medium in Petri dishes. Introduction of microbes into or on to these media is called inoculation. The nature of the medium depends on the microorganism's natural environment and on the reason why it is being grown. Normally, to isolate large numbers of microbes, liquid culture is used but solid medium is used for the isolation of individual bacteria and for storage. As bacteria are a very differing group of microbes that can exist in a wide range of environments, the ingredients in the medium will depends on the individual species. Temperature Most bacteria have characteristic temperature ranges of growth with a maximum, minimum and optimum growth temperature. Certain bacteria have become adapted to living at temperatures as low as -10OC, while having an optimum growth temperature of around 20OC. Oxygen Concentration Bacteria vary in their requirements for oxygen, depending on the nature of their metabolism. ...read more.


Growth at high osmolarity is dependent on whether the microbe has the ability to maintain a high osmolarity within the cell without damaging cellular metabolism. In the laboratory, water activity and pH are controlled by the composition of the medium. Incubators are used to provide the correct temperature. Aeration to provide adequate O2 levels is normally achieved by shaking liquid cultures or by providing large surfaces of solid medium. Anaerobic conditions can be obtained b simply filling a bottle to the top with medium so that there is not much room for air, but for more stringent anaerobes, a reducing agent such as thioglycolate may be added to the medium. Apparatus The techniques applied and apparatus used in micro-organisms play an important part in the outcome of the product. These techniques may include stirring, fermentation and the extraction of the product. For an industry to achieve optimum condition to grow micro-organisms; the environment in which they are grown should be free from any sort of contamination but 100% contamination is very hard to achieve. ...read more.


Different fermentations produce a wise range of end-products, some of which are commercially valuable. For example, dairy products such as cheese and yoghurt are produced by the activity of bacteria - Lacotbacillus and Streptococcus, which produce lactic acid as a fermentation product. Industrial fermentation may be divided into two types: batch fermentation and continous fermentation. Batch Fermentation A tank of fermenter is filled with the prepared mash of raw materials to be fermented. The temperature and pH for microbial fermentation is properly adjusted, and occasionally nutritive supplements are added to the prepared mash. The mash is steam sterilized in a pure culture process. The inoculum of a pure culture is added to the fermenter, from a separate pure culture vessel. Fermentation proceeds, and after the proper time the contents of the fermenter, are taken out for further processing. The fermenter is cleaned and the process is repeated. Thus each fermentation is a discontinuous process divided into batches. Continuous Fermentation In continuous fermentation, the substrate is added to the fermenter contillously at a fixed rate. This maintains the organisms in the logarithmic growth phase. The fermentation products are taken out continuously. The design and arrangements for continuous fermentation, are some what complex. http://www.microbiologyprocedure.com/industrial-microbiology/continuous-fermentation-process.htm ...read more.

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