Inhibition of glucose assimilation in Auxenochlorella protothecoides by light

Abstract

Background The yield of microalgae biomass is the key to affect the accumulation of fatty acids. A few microalgae can assimilate organic carbon to improve biomass yield. In mixotrophic cultivation, microalgae can use organic carbon source and light energy simultaneously. The preference of the main energy source by microalgae determines the biomass yield. Auxenochlorella protothecoides is an oleaginous mixotrophic microalga that can efficiently assimilate glucose and accumulate a large amount of biomass and fatty acids. The current study focused on the effect of light on the growth and glucose assimilation of A. protothecoides. Results In this study, we found that the uptake and metabolism of glucose in A. protothecoides could be inhibited by light, resulting in a reduction of biomass growth and lipid accumulation. We employed comparative proteomics to study the influence of light on the regulation of glucose assimilation in A. protothecoides. Proteomics revealed that proteins involving in gene translation and photosynthesis system were up-regulated in the light, such as ribulose-phosphate 3-epimerase and phosphoribulokinase. Calvin cycle-related proteins were also up-regulated, suggesting that light may inhibit glucose metabolism by enhancing the production of glyceraldehyde-3-phosphate (G3P) in the Calvin cycle. In addition, the redox homeostasis-related proteins such as thioredoxin reductase were up-regulated in the light, indicating that light may regulate glucose uptake by changing the redox balance. Moreover, the increase of NADH levels and redox potential of the medium under illumination might inhibit the activity of the glucose transport system and subsequently reduce glucose uptake. Conclusions A theoretical model of how glucose assimilation in A. protothecoides is negatively influenced by light was proposed, which will facilitate further studies on the complex mechanisms underlying the transition from autotrophy to heterotrophy for improving biomass accumulation.

Effects of Monochromatic Illumination with LEDs Lights on the Growth and Photosynthetic Performance of Auxenochlorella protothecoides in Photo- and Mixotrophic Conditions

“…The lower growth rates of illuminated cells were most probably due to a potential inhibition effect of light on A. protothecoides grown mixotrophycally. As was reported by Xiao et al [33], the proteomics analysis of A. protothecoides cultivated in glucose revealed that light had an apparent restrictive effect on the metabolic process of organic carbon assimilation. In addition, it was demonstrated here that the mixotrophic conditions also affected the photosynthetic process and the photosynthetic apparatus heterogeneity of A. protothecoides.…”

Continuous Culture of Auxenochlorella protothecoides on Biodiesel Derived Glycerol under Mixotrophic and Heterotrophic Conditions: Growth Parameters and Biochemical Composition

“…Inhibition of the substrate assimilation in the presence of light has been also reported from Xiao et al [ 31 ], when A. protothecoides was cultivated mixotrophically in a continuous system utilizing glucose instead of glycerol. In that case, glucose metabolism was also found to be restricted from the presence of light leading to limited biomass and lipids production.…”

“…Light seems to have a potential inhibitory effect on A. protothecoides when grown mixotrophically, suggesting that A. protothecoides is not favored by the mixotrophic conditions, probably due to a combination of reduced organic carbon assimilation and lower photosynthetic performance. Inhibition of the substrate assimilation in the presence of light has been also reported from Xiao et al [31], when A. protothecoides was cultivated mixotrophically in a continuous system utilizing glucose instead of glycerol. In that case, glucose metabolism was also found to be restricted from the presence of light leading to limited biomass and lipids production.…”

Influence of Light Conditions on Microalgae Growth and Content of Lipids, Carotenoids, and Fatty Acid Composition

“…Microalgae (eukaryotic and prokaryotic cyanobacteria) are a large group of photoautotrophic organisms, as well as organisms capable of heterotrophic, mixotrophic, and photoheterotrophic existence [1,2]. They are adapted to life in a variety of habitats and produce biomass containing a wide variety of compounds that can be used in the food, pharmaceutical, and cosmetic industries, and for the production of biofuels, etc.…”