A Natural Algal Polyculture Outperforms an Assembled Polyculture in Wastewater-Based Open Pond Biofuel Production

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Use of diverse algal polycultures could enhance the viability of mass algal cultivation by increasing the productivity and stability of production. However, there are multiple approaches for selecting productive polycultures, ranging from a synthetic ecology approach using carefully selected laboratory strains, to collection and cultivation of naturally occurring polycultures. In this study, we compared the performance of a systematically assembled and a naturally occurring polyculture under two conditions: 1) pilot-scale, semi-continuous culture conditions and 2) grazing and resource stress conditions. The naturally occurring polyculture had 25% higher mean biomass productivity and 19% higher N-removal efficiency than the assembled polyculture under semi-continuous culture. Differences became even more pronounced under grazing and resource stress conditions; mean biomass productivity was 60% higher in the naturally occurring polyculture when exposed to stress. Lipid and protein content (% dry mass) were significantly higher in the assembled polyculture, while carbohydrate content was higher in the naturally occurring polyculture. The naturally occurring polyculture maintained higher diversity than the assembled polyculture throughout the experiment, suggesting a greater degree of niche complementarity as a potential mechanism for differences in biomass yields and nutrient uptake. Our results show that systematically engineered algal communities may not always lead to greater productivity than algal communities found in nature per se. We suggest that future studies using polycultures assembled from lab strains should test them against those occurring naturally; collectively, this would both serve as a benchmark for progress in synthetic ecology and would test whether there are generalities in the performance of natural vs. assembled polycultures.