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Front. Microbiol. | doi: 10.3389/fmicb.2019.00609

Nutrient exchange of carbon and nitrogen promotes the formation of stable mutualisms between Chlorella sorokiniana and Saccharomyces cerevisiae under engineered synthetic growth conditions.

 Rene K. Naidoo1,  Zoe F. Simpson1, Jennifer R. Oosthuizen1 and  Florian F. Bauer1*
  • 1Stellenbosch University, South Africa

Microbial biotechnological processes can be based on single species pure cultures or on multi-species assemblages. While these assemblages can be advantageous by offering more functionalities and more resilience to changing environmental conditions, they can be unpredictable and difficult to control under synthetically engineered growth conditions. To overcome the unpredictable nature of these microbial assemblages, the generation of stable mutualistic systems through synthetic ecology approaches may provide novel solutions for understanding microbial interactions in these environments. Here we establish a stable association between two evolutionarily unrelated, but biotechnologically complementary species isolated from winery wastewater; a strain of the yeast Saccharomyces cerevisiae and microalga, Chlorella sorokiniana. Yeast and microalgae were able to form obligate (interdependent) and non-obligate (facultative) mutualisms under engineered batch co-culture growth conditions. Obligate mutualism was maintained through the reciprocal exchange of carbon and nitrogen where the yeast ferments mannose to produce carbon dioxide for use by the microalga; and the microalga provides the yeast with nitrogen by metabolising nitrite to ammonium. The effect of temperature and pH on the establishment of these mutualisms was evaluated and pH was found to be a key determinant for mutualism formation under obligatory conditions. Moreover, the combinations of the two species under non-obligatory growth conditions led to improvement in growth rate and biomass production when compared to single species cultures grown under the same conditions. Such engineered mutualisms are the first step in developing stable multi-species assemblages, while providing a system to generate novel insight into the evolution of mutualistic interactions between phylogenetically distant microorganisms.

Keywords: Microalgae, yeast, engineered, Mutualism, Synthetic, Obligatory

Received: 11 Sep 2018; Accepted: 11 Mar 2019.

Edited by:

Suhelen Egan, University of New South Wales, Australia

Reviewed by:

Eric Fouilland, UMR9190 Centre pour la biodiversité marine, l'exploitation et la conservation (MARBEC), France
Stephanie G. Hays, University of California, Berkeley, United States  

Copyright: © 2019 Naidoo, Simpson, Oosthuizen and Bauer. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Florian F. Bauer, Stellenbosch University, Stellenbosch, South Africa, fb2@sun.ac.za