Dynamic metabolic modeling of heterotrophic and mixotrophic microalgal growth on fermentative wastes

Abstract

Microalgae are promising microorganisms for the production of numerous molecules of interest, such as pigments, proteins or triglycerides that can be turned into biofuels. Heterotrophic or mixotrophic growth on fermentative wastes represents an interesting approach to achieving higher biomass concentrations, while reducing cost and improving the environmental footprint. Fermentative wastes generally consist of a blend of diverse molecules and it is thus crucial to understand microalgal metabolism in such conditions, where switching between substrates might occur. Metabolic modeling has proven to be an efficient tool for understanding metabolism and guiding the optimization of biomass or target molecule production. Here, we focused on the metabolism of Chlorella sorokiniana growing heterotrophically and mixotrophically on acetate and butyrate. The metabolism was represented by 172 metabolic reactions. The DRUM modeling framework with a mildly relaxed quasi-steady-state assumption was used to account for the switching between substrates and the presence of light. Nine experiments were used to calibrate the model and nine experiments for the validation. The model efficiently predicted the experimental data, including the transient behavior during heterotrophic, autotrophic, mixotrophic and diauxic growth. It shows that an accurate model of metabolism can now be constructed, even in dynamic conditions, with the presence of several carbon substrates. It also opens new perspectives for the heterotrophic and mixotrophic use of microalgae, especially for biofuel production from wastes.

Microalgae and cyanobacteria modeling in water resource recovery facilities: A critical review

“…In addition to nutrients, the uptake of organic and/or inorganic carbon should also be considered carefully (included in 26% of articles). Carbon uptake is commonly modeled using Michaelis-Menten or Haldane kinetics, depending on whether or not the compound can be inhibitory at higher concentrations (Baroukh et al., 2017) and on the amount of existing internal carbon stores (Concas et al., 2016; Guest et al., 2013). Apart from uptake, carbon utilization is dependent on several interrelated factors that must be considered concurrently.…”

“…Apart from uptake, carbon utilization is dependent on several interrelated factors that must be considered concurrently. For example, under low light or dark conditions, algae cannot photosynthesize enough to meet maintenance requirements, so they will consume either external organic carbon (i.e., mixotrophic or heterotrophic metabolism) or stored carbohydrates/lipids (Baroukh et al., 2017; Guest et al., 2013). As a result, carbon usage should be modeled with switching functions (introduced in ASM1 (Henze et al., 1987)) to account for these factors.…”

Two-Stage Cultivation of Dunaliella tertiolecta with Glycerol and Triethylamine for Lipid Accumulation: a Viable Way To Alleviate the Inhibitory Effect of Triethylamine on Biomass

“…(12). The algal cell number was also obtained from the OD 630 value: y ϭ 3,418.3x ϩ 226.33, R 2 ϭ 0.9908, where y is the cell number (ϫ10 4 ) and x is the OD 630 value (12).…”

“…The price of biodiesel is 1.5 to 3 times more than that of the conventional fossil diesel (2). Heterotrophic cultivation of microalgae has several advantages over autotrophic cultivation, such as the elimination of light requirement, the relative simplicity of operations, and the high cell density (3,4). However, the cost of raw materials of heterotrophic cultivation accounts for 60% to 75% of the total cost of biodiesel production (3).…”

Twelve quick tips for designing sound dynamical models for bioprocesses

“…When developing a model, it is crucial to keep in mind the objectives of the model and the framework for its application. A model targeting the understanding of some metabolic processes inherently requires the user to embark on the details of the cell metabolism [4, 5]. Predicting the impact of meteorology on outdoor microalgal processes means that light and temperature must be included somewhere in the model.…”