Niche engineering demonstrates a latent capacity for fungal-algal mutualism

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Science  04 Jul 2014:
Vol. 345, Issue 6192, pp. 94-98
DOI: 10.1126/science.1253320

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It takes two to tango in restricted environments

Despite being unrelated, freeliving algae and fungi can learn to help one another out. Hom and Murray raised the green alga Chlamydomonas reinhardtii in CO2-restricted environments in the presence of the yeast Saccharomyces cerevisiae (see the Perspective by Aanen and Bisseling). The experimental setup forced the two species to depend on one another for the metabolic production of CO2, which is provided by the yeast as it consumes glucose and is needed by the alga, and ammonia, which conversely can be made from nitrite by the alga and then used by the yeast. This dependence was seen under a broad range of environmental conditions. Similar tests between other Chlamydomonas and fungal species revealed the ability to create a phylogenetically broad range of mutualisms.

Science, this issue p. 94; see also p. 29


Mutualistic symbioses shape the evolution of species and ecosystems and catalyze the emergence of biological complexity, yet how such symbioses first form is unclear. We show that an obligate mutualism between the yeast Saccharomyces cerevisiae and the alga Chlamydomonas reinhardtii—two model eukaryotes with very different life histories—can arise spontaneously in an environment requiring reciprocal carbon and nitrogen exchange. This capacity for mutualism is phylogenetically broad, extending to other Chlamydomonas and fungal species. Furthermore, we witnessed the spontaneous association of Chlamydomonas algal cells physically interacting with filamentous fungi. These observations demonstrate that under specific conditions, environmental change induces free-living species to become obligate mutualists and establishes a set of experimentally tractable, phylogenetically related, synthetic systems for studying the evolution of symbiosis.

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