CO₂ Levels Modulate Carbon Utilization, Energy Levels and Inositol Polyphosphate Profile in Chlorella

Microalgae have a growing recognition of generating biomass and capturing carbon in the form of CO₂. The genus Chlorella has especially attracted scientists' attention due to its versatility in algal mass cultivation systems and its potential in mitigating CO₂. However, some aspects of how these green microorganisms respond to increasing concentrations of CO₂ remain unclear. In this work, we analyzed Chlorella sorokiniana and Chlorella vulgaris cells under low and high CO₂ levels. We monitored different processes related to carbon flux from photosynthetic capacity to carbon sinks. Our data indicate that high concentration of CO₂ favors growth and photosynthetic capacity of the two Chlorella strains. Different metabolites related to the tricarboxylic acid cycle and ATP levels also increased under high CO₂ concentrations in Chlorella sorokiniana, reaching up to two-fold compared to low CO₂ conditions. The signaling molecules, inositol polyphosphates, that regulate photosynthetic capacity in green microalgae were also affected by the CO₂ levels, showing a deep profile modification of the inositol polyphosphates that over-accumulated by up to 50% in high CO₂ versus low CO₂ conditions. InsP₄ and InsP₆ increased 3- and 0.8-fold, respectively, in Chlorella sorokiniana after being subjected to 5% CO₂ condition. These data indicate that the availability of CO₂ could control carbon flux from photosynthesis to carbon storage and impact cell signaling integration and energy levels in these green cells. The presented results support the importance of further investigating the connections between carbon assimilation and cell signaling by polyphosphate inositols in microalgae to optimize their biotechnological applications.