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In this paper we present the results of a numerical modelling work aimed at predicting the kinetics of microalgae production in a lab-scale photobioreactor. The experimental equipment is composed of a flat-plate bioreactor exposed to the light irradiation, and of a tank equipped with a hydraulic pump to secure the culture circulation. The numerical model addresses both the hydrodynamics of the experimental equipment and the kinetics of the relevant bio-chemical reactions. The hydrodynamics of the reactor was modelled as the one of a plug flow with a longitudinal dispersion, whereas the hydrodynamics of the tank was modelled as a cascade of continuous flow stirred tank reactors. The gaseous species transfer from the liquid free surface to the atmosphere was also considered. The relevant bio-chemical processes involved were modelled using common first-order rate expressions for the microalgae growth, and the effect of both thermal and photosynthetic phenomena, as well as the inhibition effects induced by substrate limitation and oxygen excess, have been taken into account. A calibration procedure has been conducted and showed that the model is able to reproduce with a satisfactorily degree of accuracy the experimental results, thus paving the way for its use as a production forecasting tool. [ABSTRACT FROM AUTHOR]

Summary: Galdieriasulphuraria is a cosmopolitan microalga found in volcanic hot springs and calderas. It grows at low pH in photoautotrophic (use of light as a source of energy) or heterotrophic (respiration as a source of energy) conditions, using an unusually broad range of organic carbon sources. Previous data suggested that G. sulphuraria cannot grow mixotrophically (simultaneously exploiting light and organic carbon as energy sources), its photosynthetic machinery being repressed by organic carbon.Here, we show that G. sulphuraria SAG21.92 thrives in photoautotrophy, heterotrophy and mixotrophy. By comparing growth, biomass production, photosynthetic and respiratory performances in these three trophic modes, we show that addition of organic carbon to cultures (mixotrophy) relieves inorganic carbon limitation of photosynthesis thanks to increased CO2 supply through respiration. This synergistic effect is lost when inorganic carbon limitation is artificially overcome by saturating photosynthesis with added external CO2.Proteomic and metabolic profiling corroborates this conclusion suggesting that mixotrophy is an opportunistic mechanism to increase intracellular CO2 concentration under physiological conditions, boosting photosynthesis by enhancing the carboxylation activity of Ribulose‐1,5‐bisphosphate carboxylase‐oxygenase (Rubisco) and decreasing photorespiration.We discuss possible implications of these findings for the ecological success of Galdieria in extreme environments and for biotechnological applications. [ABSTRACT FROM AUTHOR]

Acetate can be efficiently metabolized by the green microalga Chlamydomonasreinhardtii. The regular concentration is 17 mM, although higher concentrations are reported to increase starch and fatty acid content. To understand the responses to higher acetate concentrations, Chlamydomonas cells were cultivated in batch mode in the light at 17, 31, 44, and 57 mM acetate. Metabolic analyses show that cells grown at 57 mM acetate possess increased contents of all components analyzed (starch, chlorophylls, fatty acids, and proteins), with a three-fold increased volumetric biomass yield compared to cells cultivated at 17 mM acetate at the entry of stationary phase. Physiological analyses highlight the importance of photosynthesis for the low-acetate and exponential-phase samples. The stationary phase is reached when acetate is depleted, except for the cells grown at 57 mM acetate, which still divide until ammonium exhaustion. Surprisal analysis of the transcriptomics data supports the biological significance of our experiments. This allows the establishment of a model for acetate assimilation, its transcriptional regulation and the identification of candidates for genetic engineering of this metabolic pathway. Altogether, our analyses suggest that growing at high-acetate concentrations could increase biomass productivities in low-light and CO2-limiting air-bubbled medium for biotechnology. [ABSTRACT FROM AUTHOR]