Wednesday, June 22, 2005

Photosynthesis without the sun

A group of researchers (Beatty et al. 2005) have isolated an "obligately photosynthetic bacterial anaerobe" from the waters near a deep-sea hydrothermal vent. In other words, the researchers have found a bacterium that lives solely on energy gathered through photosynthesis living in an environment (the bottom of the ocean) where it has been believed that no photosynthetic organisms could survive, primarily because it's rather dark down there. The newly isolated bacterium is a species of green sulfur bacteria; all known green sulfur bacteria are phototrophs, and they're typically adept at surviving in very low-light environments, at least partially because they have light-harvesting structures called chlorosomes.

Apparently, the radiation emitting from the (very hot) thermal vents extends into the visible range (albeit dimly), and thus the authors hypothesize that the bacteria are using this radiation as an energy source for their photosynthetic reactions, though it's possible the bacteria are also using light from chemiluminescence. Data quoted in a The Scientist summary of the article compares the amount of light coming from the hydrothermal vents to other natural environments:
Photon flux [near hydrothermal vents] at 750 nm, which is what GSB1's [the newly isolated bacterium's] bacteriochlorophylls absorb, is about the same as the solar photon flux available for a green sulfur bacterium found in the Black Sea, Van Dover told The Scientist. That bacterium has been estimated to take two to three years to divide, Beatty said.
Unfortunately I don't have access to PNAS online, and thus haven't been able to read the full article, but The Scientist has an (apparently) thorough discussion of the article, and the abstract is publicly available.

(via Covington)

Beatty, JT, J Overmann, MT Lince, AK Manske, AS Lang, RE Blankenship, CL Van Dover, TA Martinson, and FG Plumley. 2005. An obligately photosynthetic bacterial anaerobe from a deep-sea hydrothermal vent. Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0503674102 (abstract).

[Update: I just discovered that Carl Zimmer has also written a short summary of this paper; he even links this discovery with a proposed mechanism for the evolution of photosynthetic processes in all life. Neat stuff.]

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