The Contribution Ratio of Autotrophic and Heterotrophic Metabolism during a Mixotrophic Culture of Chlorella sorokiniana

Abstract

The contribution ratio of autotrophic and heterotrophic metabolism in the mixotrophic culture of Chlorella sorokiniana (C. sorokiniana) was investigated. At the early stage of mixotrophic growth (day 0-1), autotrophy contributed over 70% of the total metabolism; however, heterotrophy contributed more than autotrophy after day 1 due to the rapid increase in cell density, which had a shading effect in the photo-bioreactor. Heterotrophy continued to have a higher contribution until the available organic carbon was depleted at which point autotrophy became dominant again. Overall, the increase in algal biomass and light conditions in the photo-bioreactor are important factors in determining the contribution of autotrophy and heterotrophy during a mixotrophic culture.

Keywords: Chlorella sorokiniana; autotrophic metabolism; heterotrophic metabolism; mixotrophic metabolism; wastewater treatment.

Figure 1

Variations in residual organic carbon (OC) and inorganic carbon concentrations over time in artificial wastewater under mixotrophic conditions. Artificial wastewater was prepared in a modified BG11 medium with NaHCO₃ 0.5 g-C L⁻¹ and glucose 0.5 g-C L⁻¹ (error bars denote standard deviation (n = 3)).

Figure 2

Variations in the contribution ratio of autotrophic and heterotrophic metabolism during six days of the mixotrophic culture. Artificial wastewater was prepared in a modified BG11 medium with NaHCO₃ 0.5 g-C L⁻¹ and glucose 0.5 g-C L⁻¹. The contribution ratio of autotrophic and heterotrophic metabolism was calculated based on the amount of consumed NaHCO₃ and glucose, respectively.

Figure 3

Variations in chlorophyll-a (Chl-a) content and optical density (OD₆₆₀) over time under a mixotrophic cultivation. Artificial wastewater was prepared in a modified BG11 medium with NaHCO₃ 0.5 g-C L⁻¹ and glucose 0.5 g-C L⁻¹ (error bars denote standard deviation (n = 3)).