Course: SAT 170 Introductory Biotechnology

Unit 8 Learning Module

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Cell Cloning

Types of Cell and Tissue Cultures

Bacteria are very easily cultured in a relatively short period of time, often in as little as 24 hours, by placing a sample of bacterial cells on or in culture media which contains a variety of nutrients. This media can be solid, semi-solid or liquid and is often placed into petri dishes or test tubes. The density of the media depends on how much agar is used to make it. Recall from unit 6, that agar is a material isolated from the cell walls of certain algae that can be used to create a gel like matrix, such as that which is used in gel electrophoresis. A petri dish which contains nutrient rich agar can serve as a platform for the growth of bacteria. Liquid or broth media does not contain agar so the bacterial cells disperse throughout the medium creating a certain amount of opacity (or cloudiness) in the broth once the culture has been given time to grow. Many bacteria can be cultured with a basic nutrient rich medium that contains a variety of molecules including carbohydrates, polypeptides, salts, minerals and fats. Such bacteria are said to be non-fastidious. Other bacteria require more specific and complex nutrients as well as specific environmental conditions to be effectively cultured. These bacteria are said to be fastidious. Because bacteria grow so easily with minimal nutrients, they create a problem for creating pure cultures. Simply leaving a petri dish or test tube with media open to the environment will introduce bacteria into the media, even if the exposure is only momentary. Often, if you want to culture a specific type of bacteria you would use selective media which contains nutrients that promote the growth of certain bacteria and/or inhibit the growth of others. Additionally, the practice of aseptic technique should be employed for all cell and tissue cultures including bacterial cultures. Aseptic or sterile technique is a set of practices which are used to minimize contamination of tissue cultures from microorganisms, especially bacteria. These methods are also used to ensure that the bacteria that you are trying to cultivate do not escape your culture to contaminate your environment. Examples of aseptic methods are to use heat and/or disinfectants to sterilize your tools and work space and minimizing exposure of media to the environment. Figure 1: This is an example of a bacterium that has been grown on solid media. Notice the large colonies of cells present on the media.

Figure 1 | Figure 2 | Figure 3

Fungal organisms can be grown in much the same way as that which was described for bacteria. The media commonly used to culture fungi is known as Sabouraud agar. This agar differs from nutrient agar as it has a lower pH and contains an antibiotic known as gentamicin. Both of these features are used to prevent the growth of bacteria and encourage only the growth of fungi which can tolerate lower pH levels as well as gentamicin. Bacterial and fungal cultures are useful for creating protein products as we described in unit 5. These protein products can be useful in a variety of fields such as medicine and industry. We will explore more specific examples of these applications in future units. Figure 2: .This fungal culture has been grown on Sabouraud agar to prevent the growth of bacteria. Notice the fuzzy appearance of these mold cultures.

Artificial propagation of plants began through the use of “cuttings” where a portion of a mother plant would be taken to generate a complete new plant. Grafting is another method used for plant propagation. In this process a portion of a plant is cut and joined to a rootstock. The rootstock is a stem of another plant which has established roots. Once the cutting is joined with the root stock, it can use that root stock as a supply of water and nutrients for its own growth. Figure 3: These tomato plants have been grafted to an established rootstock via the small plastic clips shown here.