In article .com,
Mike Lyle wrote:

seemed to me like a man who had the references to at his fingertips;
but it's been reported recently in Britain, just as Ivan described. I
heard it on BBC Radio 4 last week, but I think it's been in New
Scientist. Ggling got, among others, the following, which is a
starting-place:
http://www.pnas.org/cgi/content/abstract/102/26/9306

Thanks for the ref, Mike. It was in our local newspaper on Wednesday.
Here's the text of the ref:

Published online before print June 20, 2005, 10.1073/pnas.0503674102
PNAS | June 28, 2005 | vol. 102 | no. 26 | 9306-9310

An obligately photosynthetic bacterial anaerobe from a deep-sea
hydrothermal vent

J. Thomas Beatty, Jörg Overmann, Michael T. Lince, Ann K. Manske,
Andrew S. Lang, Robert E. Blankenship, Cindy L. Van Dover,
Tracey A. Martinson and F. Gerald Plumley

I read the article, and it's as Ivan originally described. The
researchers found, propagated and characterised a green sulfur
bacterium from a water sample obtained from the plume of a black smoker
vent in the East Pacific Rise, which was not present in water away from
the plume. Like all GSBs, is it obligately photosynthetic, an anaerobe
which reduces CO2 to organic carbon by oxidizing sulfur compounds.
GSBs are capable of using light of extremely low intensity, and this
critter uses "geothermal radiation that includes wavelengths absorbed
by photosynthetic pigments of this organism". It's related to a couple
of well-known genera of GSB, but the authors haven't named it yet.

They speculate that the bacterium normally lives in a microbial mat
within centimeters of the vent, "eking out an existence by infrequent
harvesting of rare geothermal photons", comparing it to a GSB that
lives at 80m in the Black Sea, which has an in situ division time of
2.8 years. In culture, both grow like crazy.

There's refs to a couple of papers about a bacterium that appears to
use light as an auxiliary source of energy to supplement its
chemotrophic metabolism, but this is the first report of an obligate
phototroph that depends on geothermal light.

Extremely cool stuff. I'm always amazed and delighted when I hear
about how some organism has managed to develop an unusual livelihood in
an unlikely environment. I guess I still have a little of that
childlike sense of wonder after all these years.