The commercialization of algal biofuels and bioproducts will not be realized until major technical and economic barriers are overcome. A major technical barrier to production of feedstock – and in turn downstream products – is maintaining high productivity and stability during algal cultivation. Yet, counter to our understanding of diversity-productivity-stability relationships in natural and artificial ecosystems, the algal cultivation industry relies heavily on the monoculture model. This reliance stems from the challenges that multi-taxa communities generate for downstream processes (e.g., harvest, conversion) and product quality, as well as methodological limitations in isolating and choosing consortia members. In this work, we ask if consortia can be used to increase productivity and yield of cultivation strains including Nannochloropsis – a commonly industrially cultivated microalga due to its content of the polyunsaturated fatty acid eicosapentaenoic acid – and Chlorella. We focus on intra-genus algal consortia to maintain consistent biomass composition and minimize the challenges associated with downstream processes. Moreover, we combine traditional bacterial isolation with high throughput screening via the HiSCI (High-throughput Screening of Cell-to-cell Interactions) tool to isolate and select specific bacterial partners that enhance productivity.
Using traditional approaches, bacteria from local terrestrial and aquatic (brackish and freshwater) environments, large-scale raceways, and culture collections were isolated and co-cultured with a production strain of Nannochloropsis. The isolated bacteria had both positive and negative effects on productivity and yield. Overall, 35% of the interactions were positive, 50% were negative, and 15% were neutral. Although many of the positive interactions were weak, 20% of the co-cultures had biomass increases of 10% and 2% had increases of 20% or greater. Compared to traditional screening, the HiSCI platform offered clear benefits in efficiency. Using this platform, the productivity of a production Chlorella strain increased 45% in the presence of two bacteria, compared to the monoculture control. Intra-specific Nannochloropsis consortia were rationally constructed using a trait database of growth rates, temperature tolerances, and pest tolerances. In many cases, performance of the consortia was similar to the monoculture controls, yet we highlight a few differences. This work forms the foundation to test rationally designed intragenus algal consortia as well as empirically-based algal-bacteria consortia in the field. Ultimately, our implementation of technological improvements will help generate an economically viable route to improve algal productivity and yield.