Sometimes, substances are mixed into media, in order to suppress growth of other types of bacteria. The two normal media used in bacteriology are a clear soup-like liquid nutrient broth, usually in tubes, and nutrient agar, which is set into a jelly by the addition of a seaweed extract called agar, and when melted poured into glass or plastic Petri dishes - also known as "plates". These substancesĪre thus broken down or digested to simpler substances and the process is called extracellular digestion because it takes place outside the bacterial cells. However, in nature, bacteria can break down solid and insoluble substances by releasing enzymes into the substrate in which they are growing. Substances are normally provided dissolved in water. (similar techniques are used to grow fungi such as moulds and yeasts)īacteria will grow on practically any source of organic food which provides carbon compounds to be respired for energy, and nitrogen compounds to be incorporated into proteins for growth.
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