2. Exercise, note at the end of this document (p. 11)
References in bold are either from the textbook (Graham & Wilcox 2000) or available as pdf files on the course CD.
1.1. Suggested reading Present document.
1.2. Some basic features of cyanobacteria The Cyanobacteria or Cyanoprokaryota (also called Cyanophyceae when classified as algae) are primitive single-celled, colonial or filamentous organisms, characterized by the absence of a nucleus and other membrane-bound organelles (so-called prokaryotic cell structure; Fig.1). The reproduction takes places by binary fission in 1-3 planes, by multiple fission forming baeocytes, and by hormogonium formation. In sessile cells, the reproduction can also occur through exocites formation. Sexual reproduction is not known in this group of organisms.
They were among the first photosynthetic organisms to evolve on our Planet some 3.5 Billion years ago, capturing sunlight by means of the green pigment chlorophyll a and a combination of water-soluble phycobili-protein pigments (phycocyanin and phycoerythrin). Therefore, the cyanobacteria are primary producers as the eukariotic algae. In certain tropical regions, e.g. in the Caribbean See, Cyanobacteria constitute one of the main groups of the phytoplankton community, contributing about 20% of the total primary production (Lee, 1999).
Most planktonic species of cyanobacteria contain aerotopes or gas vesicles[called "gas vacuoles" in older literature] that control cells buoyancy, thus allowing them to accumulate and form blooms on the surface of the water surface or form the long narrow surface streaks associated with Lagmuir circulations. Other species may accumulate at specific depths because of a physiological strategy combining the capacity to form high biomasses at low light intensities and highly efficient utilization of low nutrient concentrations. Besides, some cyanobacteria have the ability to fix nitrogen (N2), which is the main source of nitrogen in the open ocean (Lee 1999).
The ecology of cyanobacteria is described in Whitton & Potts (2000).