Metabolic, Physiological, and Transcriptomics Analysis of Batch Cultures of the Green Microalga Chlamydomonas Grown on Different Acetate Concentrations

Abstract

Acetate can be efficiently metabolized by the green microalga Chlamydomonas reinhardtii. 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.

Integrating Transcriptomics and Metabolomics to Characterize Metabolic Regulation to Elevated CO2 in Chlamydomonas Reinhardtii

“…Cells were grown mixotrophically in 17-mM acetate-containing TAP medium. Acetate was considered to be depleted from the TAP medium in 2 days as previously reported (Bogaert et al 2019), and next 4 days were grown autotrophically in all cultures tested in this study, suggesting no effect of acetate in data obtained. In this experiment, the algal cells grown under 400 ppm and 1000 ppm were cultured to logarithmic phase and cell concentration was about 8.0 × 10 5 cells mL −1 , diluted to OD 680 0.1 (i.e., initial cell concentration was about 1.0 × 10 5 cells mL −1 ), and then divided into three groups of 800-mL fresh medium in 1-L conical flasks and cultured continuously for 7 days.…”

Mixotrophic growth of the extremophile Galdieria sulphuraria reveals the flexibility of its carbon assimilation metabolism

“…While mixotrophy has always beneficial consequences on respiration, its effects on photosynthesis differ depending on the microalga considered: enhancement of photosynthesis was reported in one case (Ettlia oleoabundans (Ferroni et al, 2018)), while in other algae, including the diatoms Phaeodactylum tricornutum (Liu et al, 2009;Villanova et al, 2017) and Nannochloropsis (Fang et al, 2004;Xu et al, 2004) photosynthesis was unaffected. Decreased photosynthetic activity in mixotrophy has been reported in Chlorella vulgaris (Martinez & Orus, 1991;Cecchin et al, 2018) and Chlamydomonas reinhardtii where the carbon concentrating mechanism (CCM (Bogaert et al, 2019)) and the light harvesting capacity (Perrineau et al, 2014) is decreased by acetate along with the enhancement of respiration. While it has been reported that G. sulphuraria 074G could grow in the simultaneous presence of light and a carbon source, heterotrophy seemed to prevail in these conditions, as no photosynthetic oxygen (O 2 ) production could be measured in the presence of glucose (Oesterhelt et al, 2007).…”

Dynamic light‐ and acetate‐dependent regulation of the proteome and lysine acetylome of Chlamydomonas

“…An acclimation to growth conditions can occur on several levels, which include transcriptional and translational control, as well as protein stability, product inhibition, and allosteric effects on enzyme activities (Erickson et al., 2015; Hoober, 1989; Ledford et al., 2007). The effects of acetate on photosynthesis, gene expression, and metabolite pools have already been largely established in Chlamydomonas and other green algae (Bogaert et al., 2019; Boyle and Morgan, 2009; Boyle et al., 2017; Hayashi et al., 2015; Lauersen et al., 2016; Rai et al., 2013; Roach et al., 2013; Smith et al., 2015). To utilize C 2 compounds, such as acetate, Chlamydomonas uses the glyoxylate cycle to form C 4 compounds, which can be further metabolized to amino acids or soluble carbohydrates (Lauersen et al., 2016).…”