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Oligochaete symbiont insights - Today's Nature

Geoff Read g.read at niwa.cri.nz
Tue May 22 17:42:14 EST 2001

> 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


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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