> Endosymbiotic sulphate-reducing and sulphide-oxidizing bacteria in an
> oligochaete worm. - Nature 411(6835):298 - 302.
As a follow up, the authors might be pleased to know that paper was news
in the New York Times yesterday!
May 22, 2001
Symbiosis à Trois
By HENRY FOUNTAIN
Olavius algarvensis is a gutless creature.
Harsh words but true: O. algarvensis, an inch-long tube worm that spends
its days buried in the sandy bottom of the Mediterranean, has no gut.
Instead, it has two types of symbiotic bacteria living in its tissues that help
to provide it with nutrients.
Normally, two symbiotic species would be bad for a host, because they
would compete for space and resources. Unless, of course, the symbionts
did not actually compete but benefited from each other as well as the host.
German and Swedish researchers, writing in the journal Nature, say that
such a symbiosis à trois is just what is going on in O. algarvensis. Rather
than competing, the two types of bacteria have a mutually beneficial
relationship they recycle sulfur compounds between them, in the
process providing the worm with organic carbon and consuming some of
the products of its metabolism.
Bacterium No. 1 reduces sulfates (by adding electrons, from hydrogen or
another source), producing hydrogen sulfide. Bacterium No. 2 takes the
sulfide and oxidizes it (using oxygen from the water as an electron
acceptor), producing sulfates to be used by No. 1. No. 2 fixes carbon
dioxide and produces organic carbon compounds for use by the worm.
The sulfide-oxidizing bacteria can also get sulfide from sediments. But the
fact that the oxidizing bacteria also have an internal source of sulfide from
their symbionts means that they are not dependent on an external supply.
This may enable the worm to colonize habitats where sediments are sulfide-
Copyright 2001 The New York Times Company
Geoff Read <g.read at niwa.cri.nz>
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