Bacteria, Viruses, and Protists

Historical Interest in Bacteria

How has the classification of bacteria evolved?

Early systems for classifying bacteria were based on structural and morphological elements displayed by the organisms; for example, bacterial shape, size, and the presence or absence of several elements within the bacteria cell. They were later classified by their biochemical and physiological traits, such as the best temperatures and pH ranges for growth, respiration and fermentation, and the types of carbohydrates used as an energy source. Still later classifications were based on stains (using a dye to see an organism under the microscope), such as the Gram stain (see below). More recently, with better technology, genetic and molecular characteristics are used to understand the true evolution of bacteria and their connections to other organisms.


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