Please note, you must be an educator in higher ed or maybe high school to qualify to recieve the MCI
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|Proper care and maintenance of microorganisms is essential for any successful experiments, be they in academic research, industry or the health field. If you do not understand what a microbe requires for growth it is very difficult to study its properties. Even in the field of environmental microbiology, where unculturable microbes are sometimes studied, the ultimate goal will be to bring strains into the laboratory where they can be examined in detail. Microbes, despite their great metabolic diversity, have the same basic requirements for growth; a carbon source, an energy source and a source of reducing power. Carbon can come from CO2 or organic molecules, energy will come from light or chemicals and reducing power is obtained from organic or inorganic chemicals.
A successful medium for a target microbe must contain all the nutrients it needs for growth in a form that the microbe can utilize. These are mixed in an aqueous solution and then sterilized, most often by autoclaving. Ingredients that cannot stand the heat of the autoclave are often filter sterilized. Once sterilized, all the components of a medium are mixed together and the medium is then inoculated with a source of bacteria.
One of the more important properties for a microbe is the relationship of the microbe toward oxygen. Organisms capable of utilizing oxygen in their metabolism are aerobes, those that cannot are called anaerobes. Microbes can be separated into 5 categories based upon their use of oxygen. Strict aerobes require oxygen for their growth, while strict anaerobes cannot survive in the presence of oxygen. Facultative anaerobes can grow in the absence of oxygen, but grow better in its presence. Aerotolerant anaerobes have mechanisms to protect themselves from oxygen, thus being able to grow in its presence or absence, but do not use oxygen in their metabolism. Finally microaerophiles require oxygen for their metabolism, but cannot survive at atmospheric levels of oxygen (21% O2). Microaerophiles are restricted to narrow bands in between aerobic and anaerobic habitats, where the oxygen gradient is within an acceptable range. Some examples would be in a lake or pond, or wet soil.
For unicellular orgnaisms, growth is normally thought of as an increase in number. Microbes can growth very rapidly and the most heavily studied microbes grow by binary fission. A characteristic growth pattern is found when microbes are growth in a closed vessel. Initially, the microbe adapts to a fresh medium and no growth is observed. This is called lag phase. The microbe then begins dividing and the increase in population occurs by a geometric progression, resulting in explosive growth until nutrients are used up or toxic end products accumulate. This is termed exponential growth phase. At this stage growth stops and stationary phase begins. The population remains constant, sometimes for long periods of time. Eventually, cells accumulate damage and begin to die. The decrease in population, called death phase, occurs exponentially.
The rate of growth can be calculated by determining the cell number at different times. The growth rate (k) is a measure of how rapidly the cells are dividing, the faster cells are growing, the higher the growth rate will be.