Microalgae for the production of lipid and carotenoids: a review with focus on stress regulation and adaptation

Abstract

Microalgae have drawn great attention as promising sustainable source of lipids and carotenoids. Their lipid and carotenoids accumulation machinery can be trigged by the stress conditions such as nutrient limitation or exposure to the damaging physical factors. However, stressful conditions often adversely affect microalgal growth and cause oxidative damage to the cells, which can eventually reduce the yield of the desired products. To overcome these limitations, two-stage cultivation strategies and supplementation of growth-promoting agents have traditionally been utilized, but developing new highly adapted strains is theoretically the simplest strategy. In addition to genetic engineering, adaptive laboratory evolution (ALE) is frequently used to develop beneficial phenotypes in industrial microorganisms during long-term selection under specific stress conditions. In recent years, many studies have gradually introduced ALE as a powerful tool to improve the biological properties of microalgae, especially for improving the production of lipid and carotenoids. In this review, strategies for the manipulation of stress in microalgal lipids and carotenoids production are summarized and discussed. Furthermore, this review summarizes the overall state of ALE technology, including available selection pressures, methods, and their applications in microalgae for the improved production of lipids and carotenoids.

Keywords: Adaptive laboratory evolution; Carotenoids; Growth-promoting agents; Lipid; Microalgae; Stress.

Fig. 1

Oxidative damage under stress conditions and manipulation of stresses by transcriptional engineering. GSH glutathione, ER endoplasmic reticulum

Fig. 2

Effects of typical nutrient- and environmental stresses on the production of lipid and carotenoids in microalgae, and the resulting two-stage cultivation strategies used to overcome the biomass limitation imposed by the stress conditions

Fig. 3

Adaptive laboratory evolution (ALE) can be performed in the laboratory using three broad approaches. A Serial transfer can be performed in shake flasks with liquid medium where nutrients will not be limited, and an aliquot of the culture is transferred to a new flask with fresh medium for an additional round of growth at regular intervals. B Colony transfer is similar to serial transfer, but is performed on plates with solid medium. C A chemostat comprises a culture vessel in which the population grows under continuous agitation and aeration. Fresh medium is added into the vessel at a defined rate and culture broth is harvested continuously during the process. The figures a, b, and c illustrate the number of cells that grew during ALE the processes shown in A, B, and C, respectively (This figure was modified from Jeong et al. [112])