Day 1 Handout:
Collection of Microbes

Although bacteria generally grow in the soil, water, food, or on us, microbiologists have developed methods to grow bacteria in the lab to make them easier to study. Growth of microbes is possible only if the proper physical and chemical conditions are provided.

An example of a physical condition for microbial growth is heat. This is why we all use refrigerators to slow the growth of microbes. For the purposes of this lab, all microbes collected will be grown at 300C (about 860F).

The chemical conditions needed for microbial growth are basically the same conditions that all life needs to grow. They need water, minerals, a carbon source (such as sugar), and sources of nitrogen and energy. Some bacteria also need vitamins and amino acids (the building blocks of proteins).

Microbiologists provide all of these nutrients in substances known as media. There are two categories of media: defined and complex.

Defined media is composed of pure chemicals in carefully measured concentrations. Therefore, the exact chemical makeup of these media are known, or defined. In defined media, there are often just enough nutrients to get bacteria to grow. Some bacteria cannot grow in defined media.

Complex media are very rich in nutrients. They often contain liquefied parts of a plant or animal, so the exact amounts of the chemicals are not known. Therefore this media is called complex. We will be using complex media for our experiments. (WHY??)

We can make media in either liquid or solid form. Liquid media, or broth, contains nutrients dissolved in water. Solid media, on petri dishes, contains nutrients dissolved in water plus agar, a chemical that makes the media solid. We'll mostly use solid media, but will put the bacteria into broth later.