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Bacteria: One of the three domains of life (the others being Eukarya and Archaea), also called Eubacteria. They are unicellular prokaryotic microorganisms which generally possess rigid cell walls, multiply by cell division, and exhibit three principal forms: round or coccal, rodlike or bacillary, and spiral or spirochetal. Bacteria can be classified by their response to Oxygen: aerobic, anaerobic, or facultatively anaerobic; by the mode by which they obtain their energy: chemotrophy (via chemical reaction) or Phototrophy (via light reaction); for chemotrophs by their source of chemical energy: Chemolithotrophy (from inorganic compounds) or chemoorganotrophy (from organic compounds); and by their source for Carbon; Nitrogen; etc.; Heterotrophy (from organic sources) or Autotrophy (from Carbon dioxide). They can also be classified by whether or not they stain (based on the structure of their Cell walls) with Crystal violet dye: gram-negative or gram-positive.

Culturing and Enumerating Bacteria from Soil Samples

JoVE 10099

Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - Arizona University
Demonstrating Authors: Bradley Schmitz and Luisa Ikner

Surface soils are a heterogeneous mixture of inorganic and organic particles that combine together to form secondary aggregates. Within and between the aggregates are voids or pores that visually contain both air and water. These conditions create an ideal ecosystem for bacteria, so all soils contain vast populations of bacteria, usually over 1 million per gram of soil. Bacteria are the simplest of microorganisms, known as prokaryotes. Within this prokaryotic group, there are the filamentous microbes known as actinomycetes. Actinomycetes are actually bacteria, but they are frequently considered to be a unique group within the classification of bacteria because of their filamentous structure, which consists of multiple cells strung together to form hyphae. This experiment uses glycerol case media that select for actinomycete colonies, during dilution and plating. Typically, actinomycetes are approximately 10% of the total bacterial population. Bacteria and actinomycetes are found in every environment on Earth, but the abundance and diversity of these microbes in soil is unparalleled. These microbes are also essential for human life and affect what people eat


 Environmental Microbiology

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