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A drawing of a tree. The base of the tree reads: Radix Monera. This branches into three branches labeled Plantae, Protista, and Animalia. Each of these branches branch further; each new branch Is labeled in small text and clusters of branches are identified. For example, clusters of branches in the protista include: Diatomase, flagellate, protoplasta, and spongae.
Ernst Haeckel’s rendering of the tree of life, from his 1866 book General Morphology of Organisms , contained three kingdoms: Plantae, Protista, and Animalia. He later added a fourth kingdom, Monera, for unicellular organisms lacking a nucleus.

Nearly 100 years later, in 1969, American ecologist Robert Whittaker (1920–1980) proposed adding another kingdom—Fungi—in his tree of life. Whittaker’s tree also contained a level of categorization above the kingdom level—the empire or superkingdom level—to distinguish between organisms that have membrane-bound nuclei in their cells ( eukaryote s ) and those that do not ( prokaryote s ). Empire Prokaryota contained just the Kingdom Monera. The Empire Eukaryota contained the other four kingdoms: Fungi, Protista, Plantae, and Animalia. Whittaker’s five-kingdom tree was considered the standard phylogeny for many years.

[link] shows how the tree of life has changed over time. Note that viruses are not found in any of these trees. That is because they are not made up of cells and thus it is difficult to determine where they would fit into a tree of life.

This timeline begins with Carolus Linnaeus who developed a new way to categorize plants and animals in 1758. The image above Linnaeus shows a forked line with one branch labeled plants and the other labeled animals. In 1866, Ernst Haeckel wrote General Morphology of Organisms, proposing four kingdoms. The image above Haeckel shows a central line with Monera branching off the bottom, protists branching off next, then plants and finally animals. In 1969 Robert Whittaker proposed adding a fifth kingdom – fungi – to the tree of life. The image above Whittaker is the same as the one above Haeckel but includes an additional branch labeled fungi between plants and animals.
This timeline shows how the shape of the tree of life has changed over the centuries. Even today, the taxonomy of living organisms is continually being reevaluated and refined with advances in technology.
  • Briefly summarize how our evolving understanding of microorganisms has contributed to changes in the way that organisms are classified.

Part 2

Antibiotic drugs are specifically designed to kill or inhibit the growth of bacteria. But after a couple of days on antibiotics, Cora shows no signs of improvement. Also, her CSF cultures came back from the lab negative. Since bacteria or fungi were not isolated from Cora’s CSF sample, her doctor rules out bacterial and fungal meningitis. Viral meningitis is still a possibility.

However, Cora now reports some troubling new symptoms. She is starting to have difficulty walking. Her muscle stiffness has spread from her neck to the rest of her body, and her limbs sometimes jerk involuntarily. In addition, Cora’s cognitive symptoms are worsening. At this point, Cora’s doctor becomes very concerned and orders more tests on the CSF samples.

  • What types of microorganisms could be causing Cora’s symptoms?

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The role of genetics in modern taxonomy

Haeckel’s and Whittaker’s trees presented hypotheses about the phylogeny of different organisms based on readily observable characteristics. But the advent of molecular genetics in the late 20th century revealed other ways to organize phylogenetic trees. Genetic methods allow for a standardized way to compare all living organisms without relying on observable characteristics that can often be subjective. Modern taxonomy relies heavily on comparing the nucleic acids (deoxyribonucleic acid [DNA] or ribonucleic acid [RNA]) or proteins from different organisms. The more similar the nucleic acids and proteins are between two organisms, the more closely related they are considered to be.

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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