Early Changes in Nutritional Conditions Affect Formation of Synthetic Mutualism Between Chlorella sorokiniana and the Bacterium Azospirillum brasilense
The effect of three different nutritional conditions during the initial 12 h of interaction between the microalgae Chlorella sorokiniana UTEX 2714 and the plant growth–promoting bacterium Azospirillum brasilense Cd on formation of synthetic mutualism was assessed by changes in population growth, production of signal molecules tryptophan and indole-3-acetic acid, starch accumulation, and patterns of cell aggregation. When the interaction was supported by a nutrient-rich medium, production of both signal molecules was detected, but not when this interaction began with nitrogen-free (N-free) or carbon-free (C-free) media. Overall, populations of bacteria and microalgae were larger when co-immobilized. However, the highest starch production was measured in C. sorokiniana immobilized alone and growing continuously in a C-free mineral medium. In this interaction, the initial nutritional condition influenced the time at which the highest accumulation of starch occurred in Chlorella, where the N-free medium induced faster starch production and the richer medium delayed its accumulation. Formation of aggregates made of microalgae and bacteria occurred in all nutritional conditions, with maximum at 83 h in mineral medium, and coincided with declining starch content. This study demonstrates that synthetic mutualism between C. sorokiniana and A. brasilense can be modulated by the initial nutritional condition, mainly by the presence or absence of nitrogen and carbon in the medium in which they are interacting.
KeywordsPGPB Microalgae Interaction Signal molecules Nutritional effects Starch
At CIBNOR, Mexico, we thank Manuel Moreno, Francisco Hernandez, and Patricia Hinojosa for technical assistance.
OAP and BRL designed and executed the study and wrote the initial draft. YB critically revised the article for intellectual content including the final version. LEdeB designed and managed the project and critically revised the manuscript. All the authors read and approved the manuscript.
This work was financially supported by Consejo Nacional de Ciencia y Tecnología of Mexico (CONACYT Basic Science-2015, contract 251102 and CONACYT Basic Science-2017, contract 284562) and the actual drafting of the paper was supported by The Bashan Foundation, USA. This is contribution 2018-027 of the Bashan Institute of Science, USA.
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
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