171 Environmental Microbiology and Water Quality Experiment 1: Bacteria Isolation from Soil Samples A typical soil sample has billions of microorganisms due to its moist, nutrient rich composition. Common soil- inhabiting bacteria include: Bacillus, Streptomyces, Pseudomonas, Micrococcus, coliforms (indicators of fe- cal contaminants), lactic acid bacteria, and Clostridium. Various fungi (molds) are also frequently found in soil samples. These organisms play a critical role in the different natural biogeochemical cycles. Bacteria meet their nutrient needs by metabolizing organic matter (decomposing plants and animals) in soil, thereby oxidizing and reducing the elements in the organic matter and returning those elements to the environment. In this experiment, you will examine the diversity of soil microorganisms by culture bacteria from a soil sam- ple and performing some microbiological tests to attempt to identify the microbes. Procedure: Prepare Nutrient Agar Plates: 1. Loosen or remove the cap on the nutrient agar bottle. 2. Place the bottle in a microwave (if you do not have a microwave, place the bottle in a heat-safe bowl and pour boiling water around the bottle) and heat until the entire bottle of agar is liquefied. You will need to remove the bottle and swirl every 10 seconds to distribute the heat. Note: If you notice the agar boiling over, STOP the microwave and let the bottle cool down before han- dling. Hot agar can violently explode out of the bottle if heated too quickly and/or shaken. After boiling has stopped, use a hot pad protecting your hands and remove the bottle from the microwave. Use caution when removing the bottle from the microwave as it will be HOT! Sterile saline 3 Sterile spreaders (9) 15 mL Conical tubes with screw tops 250 mL Beaker 10 Sterile disposable transfer pipettes (8) 5 cm. Petri dishes Nutrient agar Parafilm ™ 1 Pair of gloves Permanent marker Hot pad 10 mL Graduated cylinder *1 tsp. Soil sample *Microwave or other boiling water bath *Refrigerator *10% Bleach solution *You must provide Materials
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171
Environmental Microbiology and Water Quality
Experiment 1: Bacteria Isolation from Soil Samples A typical soil sample has billions of microorganisms due to its moist, nutrient rich composition. Common soil-