Piezophilic Bacteria
- PDF / 191,941 Bytes
- 5 Pages / 595.276 x 790.866 pts Page_size
- 18 Downloads / 196 Views
PIEZOPHILIC BACTERIA
is then reduced to glyceraldehyde-3-phosphate which can be used to form glucose or other organic compounds. However, only one of six glyceraldehyde-3-phosphate molecules leaves the Calvin cycle while the rest is used for the regeneration of the carbon dioxide acceptor ribulose-1,5-bisphosphate which requires more ATP (Figure 1b; for more details on Calvin cycle, see, e.g., Lawlor, 2001; Heldt, 2003).
Anoxygenic photosynthesis Anoxygenic photosynthesis, which can be found in purple bacteria, green sulfur bacteria, green non-sulfur bacteria, and heliobacteria, differs from oxygenic photosynthesis in that it requires only one photosystem and, since no splitting of water occurs, no oxygen is produced. The photosystem used by purple bacteria and green nonsulfur bacteria is similar to the PSII of plants and cyanobacteria, but contains bacteriochlorophyll instead of chlorophyll. The electron transport is cyclic since the electrons return to the reaction center after passing through a series of electron carriers. The product of the electron transport in the photosystem is ATP. Purple bacteria and green nonsulfur bacteria must oxidize inorganic or organic compounds such as H2S, H2, succinate, or malate to provide the reduction potential necessary for carbon fixation. By using these compounds as electron donors, NADþ (nicotinamide adenine dinucleotide) is reduced to NADHþHþ in a process called reverse electron transport. Purple bacteria use the Calvin cycle to fix carbon dioxide while green non-sulfur bacteria use a special process called 3-hydroxypropionate pathway. Green sulfur bacteria and heliobacteria contain a photosystem that resembles the PSI of oxygenic photosynthetic organisms. It has a cyclic electron flow, but here NADþ can be reduced directly. Green sulfur bacteria use the reverse Krebs cycle to fix carbon dioxide, while heliobacteria are photoorganotrophs (for more details on anoxygenic photosynthesis, see, e.g., Whitmarsh and Govindjee, 1999; Madigan et al., 2009). Summary The light reactions of photosynthesis use the energy of sunlight to provide chemical energy and reducing power in the form of ATP and NADPHþHþ, respectively, which can then be used in the light-independent reactions to fix carbon dioxide and to convert it into carbohydrates. During the oxygenic photosynthesis of plants and cyanobacteria, water is split and dioxygen is released, whereas anoxygenic photosynthetic organisms such as purple bacteria, green sulfur bacteria, green nonsulfur bacteria, and heliobacteria do not produce oxygen. Bibliography Björn, L. O., and Govindjee, 2009. The evolution of photosynthesis and chloroplasts. Current Science, 96, 1466–1474. Heldt, H. W., 2003. Pflanzenbiochemie. Heidelberg: Spektrum Akademischer Verlag.
Lawlor, D. L., 2001. Photosynthesis. Oxford: BIOS Scientific Publishers. Madigan, M. T., Martinko, J. M., Dunlap, P. V., and Clark, D. P., 2009. Brock Biology of Microorganisms. San Francisco: Pearson Benjamin Cummings. Renger, G., 2010. The light reactions of photosynthesis. Curre
Data Loading...
