lab_11_physical_growth_requirements

lab_11_physical_growth_requirements - Miramar College...

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Lab Exercise 11: Physical Growth Requirements Page 1 of 5 Miramar College Biology 205 Microbiology Lab Exercise 11: Physical Growth Requirements Background Microorganisms, like any other living thing, require an external environment that is tailored to their specific metabolic needs and capabilities. The ability to grow in a specific environment relies on the presence of certain genes and proteins that make growth possible. For instance, growth in salty environments requires that a microorganism possess the genes to produce and orient compatible solutes to offset the increased osmotic pressure of their hypertonic environment. Likewise, growth in an alkaline environment requires the production of proteins that can offset the overabundance of hydroxyl ions and the charge differential of the environment. Even in our so-called normal environment, a myriad of enzymes are required to combat the would-be toxic effects of simply living in the presence of oxygen. Although the aspects of the external physical environment are infinite, three basic requirements are the focus of study in this microbiology lab: oxygen ; temperature and pH . Each organism, although capable of growth outside their “optimal” environment, will grow best when certain aspects of the environment are kept at a constant, optimal level. It is important, when characterizing a microorganism, to take the time to investigate the environmental parameters that will allow the organism to grow at optimal levels. When environmental conditions are optimized, organisms can grow to their full biotic potential- something that happens only in highly controlled laboratory situations such as exist in bioreactors . Even in our microbiology lab we can control only the most basic aspects of the environment and so, although growth in vitro can be markedly faster than in situ growth, it doesn’t even approach biotic potential. Assuming an optimal generation time of 20 minutes, a single Escherichia coli will grow to 10 9 (that’s a billion!) cells in just 10 hours. If that’s not impressive enough, that same E. coli ’s progeny will weigh as much as the earth in little more than 24 hours (the earth weighs 5.9 × 10 24 kg, the E. coli would weigh 4.7 ×10 21 kg in 24 hours). Oxygen All organisms are categorized based on their tolerance of and need for oxygen. Those organisms who require atmospheric levels of oxygen (~20%) for growth and survival are termed obligate aerobes ; organisms that require oxygen at less than atmospheric levels (~5–10%) are called microaerophiles ; organisms who cannot grow in the presence of oxygen are called obligate anaerobes ; organisms that do not use oxygen for metabolism but can grow in its presence are termed aerotolerant anaerobes and organisms that will grow preferentially with oxygen but are capable of growth without it are called facultative anaerobes . The oxygen requirements of a given organism can be easily determined in the microbiology laboratory by the use of both solid and liquid media. Investigating oxygen requirements using solid media requires the use of an
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This note was uploaded on 12/23/2009 for the course BIO 205 taught by Professor Murphy during the Fall '09 term at Miramar College.

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lab_11_physical_growth_requirements - Miramar College...

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