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Summary 1

I. What are Cyanobacteria? 1

II. Ecological Diversity in the Past and Present 1

III. Morphological Diversity 3

IV. Taxonomy 4

V. Molecular Ecology 7

VI. InteractionswithOtherOrganisms 8

VII. Blooms and Toxins 8

VIII. Cyanobacteria as Health Food 8

IX. Use of Cultures and Culture Media 9

Summary

This chapter is written largely for those who are not already specialists in the cyanobacteria. Features of these organisms are introduced by highlighting some of the topics described in the various chapters, together with other important subjects for which there was no space for a dedicated chapter. The reason is explained why cyanobacteria were formerly known as blue-green algae, and frequently still are known under this name by those involved in water management.

I. What are Cyanobacteria?

Cyanobacteria are photosynthetic prokaryotes possessing the ability to synthesize chlorophyll a. Typically water is the electron donor during photosynthesis, leading to the evolution of oxygen. Cyanobacteria have until recently also been characterized by their ability to form the phycobilin pigment, phycocyanin. It is the high concentration of this pigment occurring under some conditions which leads to the bluish colour of the organisms (Plate 2a, 2e) and hence both of the names by which the organisms are commonly known, cyanobacteria or blue-green algae. However, it has increasingly become clear that at least some oxygen-evolving prokaryotes such as Prochlorothrix, which do not possess phycobilins, but do form chlorophyll b in addition to chlorophyll a (Post, 1999; Tomitani et al., 1999), are quite closely related to organisms with phycocyanin. As the molecular evidence does not support the grouping together of all these chlorophyll-^ -containing organisms, they are treated here (Chapter 5) as members of the cyanobacteria in the broadest sense (but see p. 532).

II. Ecological Diversity in the Past and Present

Geologists and geochemists all agree that cyanobacteria have had a long evolutionary history and most - though not all - agree that this extends to

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