An Engineered Community Approach for Industrial Cultivation of Microalgae

Abstract

Although no species lives in isolation in nature, efforts to grow organisms for use in biotechnology have generally focused on a single-species approach, particularly where a product is required at high purity. In such scenarios, preventing the establishment of contaminants requires considerable effort that is economically justified. However, for some applications in biotechnology where the focus is on lower-margin biofuel production, axenic culture is not necessary, provided yields of the desired strain are unaffected by contaminants. In this article, we review what is known about interspecific interactions of natural algal communities, the dynamics of which are likely to parallel contamination in industrial systems. Furthermore, we discuss the opportunities to improve both yields and the stability of cultures by growing algae in multi-species consortia.

Fig. 1

Absorption spectra of pigments present in algae shown in comparison to the intensity of the sun’s radiation at the Earth’s surface. In vivo absorption spectra are shown for chlorophyll a (λ_max = 435, 665 nm), chlorophyll b (λ_max = 480, 650 nm), chlorophyll c (λ_max = 645 nm), β-carotene (λ_max = 450 nm), phycoerythrin (λ_max = 490, 546, 576 nm), and phycocyanin (λ_max = 618 nm).

Fig. 2

Survival of Daphnia pulex (water flea) in cultures of algae with different species composition, taken from a study by Shurin et al. In this experiment, animals were added to 25-day-old cultures of algae composed of either one, two, five, or ten algal species (belonging to the groups Chlorophyta, Cyanophyta, Bacillariophyta and Heterokontophyta) and the number of cultures in which the fleas survived was assessed daily. For each combination, three biological repeats were assayed. The photograph is an image of Daphnia under the light microscope at 10× magnification.

Fig. 3

An engineered symbiotic interaction described by Ortiz-Marquez et al., in which a nitrogen-fixing bacterium, Azotobacter vinelandii, was modified to express constitutively a nitrogenase (ΔnifL) providing ammonium for non-diazotrophic organisms (unable to fix nitrogen), including the green algae Chlorella sorokiniana and Scenedesmus obliquus.