Free-Living Protozoa with Endosymbiotic Methanogens
Methanogenic bacteria occur in many, but not all free-living obligate anaerobic protozoa. This sort of symbiosis is especially common among anaerobic ciliates, but is also found in a few species of amoebae and flagellates. Protozoa harbouring methanogens
- PDF / 355,943 Bytes
- 11 Pages / 439.37 x 666.142 pts Page_size
- 59 Downloads / 176 Views
Contents 1 Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Morphology and Life Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Significance of the Association . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5 Intracellular H2-Tension and Methanogens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6 Symbiotic Consortia as Natural Chemostats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7 The Role of Symbiotic Methanogenesis in Natural Habitats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Abstract Methanogenic bacteria occur in many, but not all free-living obligate anaerobic protozoa. This sort of symbiosis is especially common among anaerobic ciliates, but is also found in a few species of amoebae and flagellates. Protozoa harbouring methanogens have a clostridium-type fermentative metabolism with H2 as metabolite, the hydrogen generation taking place in special organelles, so called hydrogenosomes. The relation between the host cells and their endosymbiotic methanogens is syntrophic hydrogen transfer. By removing the generated H2, the methanogens stimulate host H2-production, thus increasing the energetic yield of the energy metabolism. This sort of symbiosis has evolved independently in many cases and involves representatives of several major groups of methanogenic bacteria. Symbiotic methanogenesis of free-living anaerobic protozoa plays only a modest quantitative role in terms of CH4-production in most habitats. T. Fenchel (*) Marine Biological Laboratory, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark e-mail: [email protected] B.J. Finlay Queen Mary University of London, The River Laboratory, Wareham, Dorset BH20 6BB, UK e-mail: [email protected]
J.H.P. Hackstein (ed.), (Endo)symbiotic Methanogenic Archaea, Microbiology Monographs 19, DOI 10.1007/978-3-642-13615-3_1, # Springer-Verlag Berlin Heidelberg 2010
1
2
T. Fenchel and B.J. Finlay
1 Discovery It was discovered earlier that sulphidic aquatic habitats rich in decaying organic matter – so called sapropel – harbour special and characteristic protozoan biota (Lauterborn 1901), and throughout the twentieth century a number of such sapropelic protozoa were described including flagellates, amoeboid organisms and, not least, ciliates from such
Data Loading...
