The Eukaryotic Members of the Microbial World

Jn Salem Village, Massachusetts, in 1692, a group of teenage girls was afflicted with symptoms of "bewitchment." They suffered convulsions; had sensations of being pinched, pricked, or bitten; and had feelings of being torn apart. Some became temporarily blind, deaf, or speechless and were sick to their stomachs. During the inquest into their bewitchment, the girls accused several women of being instruments of the devil. These women were tried and then executed as witches.

Recently, some historians have reexamined this event and, with the help of the medical and biological community, have concluded that the Salem witch hunts may have been more a microbiological phenomenon, than a social phenomenon. A member of the microbial world may have been the culprit. The fungus Claviceps purpurea, the rye smut, produces the poison ergot, which when ingested causes symptoms similar to those experienced by the girls in Salem. Apparently, several conditions existed in New England at this time that would have predisposed the population to ergot poisoning. First, the years 1690 to 1692 were particularly wet and cool. Second, during those years, rye grass had replaced wheat in New England as the principal grain because the wheat was seriously affected by another fungus, the wheat rust. In addition, most of the victims were children and teenagers who would have been more affected by ergot poisoning than adults because they would have ingested more of the poison per body weight than adults.

This is only one highly publicized example of the way in which microbes have played a large role in the history of the world.

—A Glimpse of History

AS NOTED AT THE BEGINNING OF THIS BOOK, when the ribosomal RNA (rRNA) sequences of organisms are compared, the living world can be divided into three divisions: Bacteria, Archaea, and Eucarya. In this chapter we will consider the Eucarya. These organisms, which include the algae, fungi, protozoa, multicellular parasites, and insect vectors, have one feature in common: they are all eukaryotic organisms. Recall from chapter 3 that the basic cell structure of the Eucarya is distinctly different from that of the Bacteria and Archaea. They are included in a textbook of microbiology because many members of these groups are microscopic and are studied with techniques that are similar to those used to study bacteria and archaea. In addition, many of these organisms cause disease in humans as well as plants and animals. ■ Eucarya, pp. 9,247

Classification using gross anatomical characteristics of algae, fUngi, protozoa, and even some multicellular parasites has always been problematic. Now, however, with modern techniques that examine these organisms at the molecular and ultrastructural levels, it has been discovered that some of the organisms that were traditionally grouped together were more dissimilar than similar. Instead, they arose at various times along a continuum of evolution. Therefore, in classification schemes that describe an accurate evolutionary history of organisms and are based on molecular and ultrastructure examination, the words algae, fungi, and protozoa are no longer really accurate. For the purposes of this book, however, we will use the term algae to describe the pho-tosynthetic members and fungi and protozoa to describe the non-photosynthetic members that are discussed in this chapter. In addition, a discussion of arthropods and helminths is included because these eukaryotes are also implicated in human disease. Figure 12.1 shows a phylogeny based on the ribosomal RNA sequences of the eukaryotic organisms. We will refer to this phylogeny throughout this chapter, highlighting where the organisms fit on this evolutionary scale.

300 Chapter 12 The Eukaryotic Members of the Microbial World Animals

- Choanoflagellates

- Zygomycetes -Ascomycetes


— Basidiomycetes -Chytridiomycetes

Chlorophytes (green algae)

■ Cryptomonads

Rhodophyta (red algae)

Chrysophyta (golden brown algae and diatoms)



Oomycetes (water molds)

Oomycetes (water molds)

Pyrrophyta - dinoflagellates


Cellular slime molds

Acellular slime molds







Figure 12.1 A Phylogeny of the Eukaryotes Based on Ribosomal RNA Sequence Comparison

Fotos Pintura Com Pontiliasmos

Figure 12.2 Algae (a) Volvox sp. a colony of cells formed into a hollow sphere (125x).The yellow-green circles are reproductive cells that will eventually become new colonies. (b) Corallina gracilis, red coral algae.

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