Anoxygenic photosynthesis

Anoxygenic photosynthesis

dark reactions", respectively).

Overview

Anoxygenic photosynthesis is the phototrophic process where light energy is captured and converted to ATP, without the production of oxygen. Water is therefore not used as an electron donor. There are several groups of bacteria that undergo anoxygenic photosynthesis: Green sulfur bacteria, green and red filamentous anoxygenic phototrophs (FAPs), phototrophic purple bacteria, phototrophic Acidobacteria, and phototrophic heliobacteria.[1][2]

Anoxygenic phototrophs have photosynthetic pigments called solvent, but are similarly red-shifted within their natural environment (with the exception of bacteriochlorophyll f, which has not been naturally observed).

Unlike oxygenic phototrophs, anoxygenic photosynthesis only functions using (by phylum) either one of two possible types of photosystem. This restricts them to cyclic electron flow and are therefore unable to produce O2 from the oxidization of H2O.

Photosynthetic electron transport chain

Purple non-sulfur bacteria

The electron transport chain of purple non-sulfur bacteria begins when the reaction centre bacteriochlorophyll pair, P870, becomes excited from the absorption of light. Excited P870 will then donate an electron to Bacteriopheophytin, which then passes it on to a series of electron carriers down the electron chain. In the process, it will generate a proton motor force (PMF) which can then be used to synthesize ATP by oxidative phosphorylation. The electron returns to P870 at the end of the chain so it can be used again once light excites the reaction-center.

Green sulfur bacteria

The electron transport chain of green sulfur bacteria uses the cytochrome c555.

References

  1. ^ [Donald A. Bryant, Niels-Ulrik Frigaard, Prokaryotic photosynthesis and phototrophy illuminated, Trends in Microbiology, Volume 14, Issue 11, November 2006, Pages 488-496, ISSN 0966-842X, 10.1016/j.tim.2006.09.001. (http://www.sciencedirect.com/science/article/pii/S0966842X06002265)]
  2. ^ Candidatus Chloracidobacterium thermophilum: An Aerobic Phototrophic Acidobacterium Donald A. Bryant, Amaya M. Garcia Costas, Julia A. Maresca, Aline Gomez Maqueo Chew, Christian G. Klatt, Mary M. Bateson, Luke J. Tallon, Jessica Hostetler, William C. Nelson, John F. Heidelberg, and David M. Ward Science 27 July 2007: 317 (5837), 523-526. DOI:10.1126/science.1143236