The Prokaryotes

KEN KILLHAM Jim I. Prosser

Introduction Phylogeny

General Features of Prokaryotes Cell Structure Metabolism and Physiology Biodegradation Capacity

Differentiation, Secondary Metabolism, and Antibiotic Production

Conclusion

References and General Reading introduction

Living organisms form three major domains: Bacteria and Archaea, collectively termed prokaryotes, and the Eucarya or eukaryotes. Eukaryotic soil organisms, including microorganisms, are discussed in Chaps. 6 and 7. Prokaryotes are distinguished from eukaryotes by the absence of a unit membrane-bound nucleus and, usually, the lack of other cell organelles. Ribosomes in prokaryotes are smaller (70S) than in eukaryotes (80S) and no eukaryote is able to fix atmospheric N2. The endosymbiotic theory (Margulis, 1993) proposes that the mitochondria and chloro-plasts of eukaryotic cells originated as symbiotic prokaryotic cells. The presence of bacterial, circular, covalently closed DNA and 70S ribosomes in mitochondria supports this theory. Despite the apparent, relative simplicity of prokaryotic cells, as a group they have the greater taxonomic and functional diversity. Globally, organic C in prokaryotes is equivalent to that in plants and they contain 10-fold more N. They also possess the most efficient dispersal and survival mechanisms. As a consequence, prokaryotes are of enormous importance in creating, maintaining, and functioning of the soil. The aim of this chapter is to provide an overview of the taxonomy and characteristics of soil prokaryotes and show their importance both for prokaryote growth and activity and for soil function.

phylogeny

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