Energy metabolism and intracellular pH regulation reveal different physiological acclimation mechanisms of Chlorella strains to high concentrations of CO2

The intolerance of high CO2 in the exhaust gas is the "bottleneck" limiting the wide application of microalgae for CO2 biosequestration. Around this topic, we selected high-CO2-tolerant (LAMB 33 and 31) and nontolerant (LAMB 122) Chlorella strains to study their different energy metabolisms and cytoplasmic pH regulations in response to high CO2. Under 40 % CO2, LAMB 33 and 31 both showed elevated ATP synthesis, accelerated ATP consumption and fast cytoplasmic pH regulation while exhibiting different acclimating strategies therein: chloroplast acclimations were reflected by high chlorophyll contents in 33 but photosystem transitions in 31; faster mitochondrial acclimations occurred in 33 than in 31; cellular organic carbon mainly flowed to monosaccharide synthesis for 33 but to monosac-charide and protein synthesis for 31; and cytoplasmic pH regulation was attributed to V-ATPase in 31 but not in 33. All the above metabolic processes gradually collapsed in 122, leading to growth inhibition. Our study identified different metabolic acclimation strategies among Chlorella strains to high CO2 and provided new traits for breeding microalgae for CO2 biosequestration.