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Abstract：
BACKGROUND: Microalgae\'s low tolerance to high CO2 concentrations presents a significant challenge for its industrial application, especially when considering the utilization of industrial exhaust gas streams with high CO2 content-an economically and environmentally attractive option. Therefore, the objectives of this study were to investigate the metabolic changes in carbon fixation and lipid accumulation of microalgae under ambient air and high CO2 conditions, deepen our understanding of the molecular mechanisms driving these processes, and identify potential target genes for metabolic engineering in microalgae. To accomplish these goals, we conducted a transcriptomic analysis of the high CO2-tolerant strain, Chlorella sp. ABC-001, under two different carbon dioxide levels (ambient air and 10% CO2) and at various growth phases.
RESULTS: Cells cultivated with 10% CO2 exhibited significantly better growth and lipid accumulation rates, achieving up to 2.5-fold higher cell density and twice the lipid content by day 7. To understand the relationship between CO2 concentrations and phenotypes, transcriptomic analysis was conducted across different CO2 conditions and growth phases. According to the analysis of differentially expressed genes and gene ontology, Chlorella sp. ABC-001 exhibited the development of chloroplast organelles during the early exponential phase under high CO2 conditions, resulting in improved CO2 fixation and enhanced photosynthesis. Cobalamin-independent methionine synthase expression was also significantly elevated during the early growth stage, likely contributing to the methionine supply required for various metabolic activities and active proliferation. Conversely, the cells showed sustained repression of carbonic anhydrase and ferredoxin hydrogenase, involved in the carbon concentrating mechanism, throughout the cultivation period under high CO2 conditions. This study also delved into the transcriptomic profiles in the Calvin cycle, nitrogen reductase, and lipid synthesis. Particularly, Chlorella sp. ABC-001 showed high expression levels of genes involved in lipid synthesis, such as glycerol-3-phosphate dehydrogenase and phospholipid-diacylglycerol acyltransferase. These findings suggest potential targets for metabolic engineering aimed at enhancing lipid production in microalgae.
CONCLUSIONS: We expect that our findings will help understand the carbon concentrating mechanism, photosynthesis, nitrogen assimilation, and lipid accumulation metabolisms of green algae according to CO2 concentrations. This study also provides insights into systems metabolic engineering of microalgae for improved performance in the future.
RESULTS: Cells cultivated with 10% CO2 exhibited significantly better growth and lipid accumulation rates, achieving up to 2.5-fold higher cell density and twice the lipid content by day 7. To understand the relationship between CO2 concentrations and phenotypes, transcriptomic analysis was conducted across different CO2 conditions and growth phases. According to the analysis of differentially expressed genes and gene ontology, Chlorella sp. ABC-001 exhibited the development of chloroplast organelles during the early exponential phase under high CO2 conditions, resulting in improved CO2 fixation and enhanced photosynthesis. Cobalamin-independent methionine synthase expression was also significantly elevated during the early growth stage, likely contributing to the methionine supply required for various metabolic activities and active proliferation. Conversely, the cells showed sustained repression of carbonic anhydrase and ferredoxin hydrogenase, involved in the carbon concentrating mechanism, throughout the cultivation period under high CO2 conditions. This study also delved into the transcriptomic profiles in the Calvin cycle, nitrogen reductase, and lipid synthesis. Particularly, Chlorella sp. ABC-001 showed high expression levels of genes involved in lipid synthesis, such as glycerol-3-phosphate dehydrogenase and phospholipid-diacylglycerol acyltransferase. These findings suggest potential targets for metabolic engineering aimed at enhancing lipid production in microalgae.
CONCLUSIONS: We expect that our findings will help understand the carbon concentrating mechanism, photosynthesis, nitrogen assimilation, and lipid accumulation metabolisms of green algae according to CO2 concentrations. This study also provides insights into systems metabolic engineering of microalgae for improved performance in the future.
摘要：
背景：微藻对高CO2浓度的低耐受性对其工业应用提出了重大挑战，特别是当考虑利用具有高CO2含量的工业废气流时-经济和环境上有吸引力的选择。因此,这项研究的目的是研究在环境空气和高CO2条件下，微藻的碳固定和脂质积累的代谢变化，加深我们对驱动这些过程的分子机制的理解，并确定微藻代谢工程的潜在目标基因。为了实现这些目标,我们对高耐二氧化碳菌株进行了转录组学分析，小球藻sp.ABC-001，在两种不同的二氧化碳水平（环境空气和10％CO2）和不同的生长阶段。
结果：用10％CO2培养的细胞表现出明显更好的生长和脂质积累速率，到第7天，细胞密度可提高2.5倍，脂质含量可提高两倍。为了理解CO2浓度和表型之间的关系，在不同的CO2条件和生长阶段进行转录组学分析。根据差异表达基因和基因本体论的分析,小球藻sp.ABC-001在高CO2条件下的早期指数期表现出叶绿体细胞器的发育，从而改善CO2固定和增强光合作用。不依赖钴胺的蛋氨酸合成酶表达在早期生长阶段也显著升高，可能有助于各种代谢活动和活跃增殖所需的蛋氨酸供应。相反，细胞表现出碳酸酐酶和铁氧还蛋白氢化酶的持续抑制，参与碳浓缩机制，在高CO2条件下的整个栽培期间。这项研究还深入研究了卡尔文循环中的转录组概况，氮还原酶,和脂质合成。特别是,小球藻sp.ABC-001显示参与脂质合成的基因的高表达水平，例如甘油-3-磷酸脱氢酶和磷脂-二酰甘油酰基转移酶。这些发现提示了旨在增强微藻中脂质产生的代谢工程的潜在目标。
结论：我们希望我们的发现将有助于理解碳浓缩机制，光合作用,氮同化，和根据CO2浓度的绿藻的脂质积累代谢。这项研究还为微藻的系统代谢工程提供了见解，以改善未来的性能。
结果：用10％CO2培养的细胞表现出明显更好的生长和脂质积累速率，到第7天，细胞密度可提高2.5倍，脂质含量可提高两倍。为了理解CO2浓度和表型之间的关系，在不同的CO2条件和生长阶段进行转录组学分析。根据差异表达基因和基因本体论的分析,小球藻sp.ABC-001在高CO2条件下的早期指数期表现出叶绿体细胞器的发育，从而改善CO2固定和增强光合作用。不依赖钴胺的蛋氨酸合成酶表达在早期生长阶段也显著升高，可能有助于各种代谢活动和活跃增殖所需的蛋氨酸供应。相反，细胞表现出碳酸酐酶和铁氧还蛋白氢化酶的持续抑制，参与碳浓缩机制，在高CO2条件下的整个栽培期间。这项研究还深入研究了卡尔文循环中的转录组概况，氮还原酶,和脂质合成。特别是,小球藻sp.ABC-001显示参与脂质合成的基因的高表达水平，例如甘油-3-磷酸脱氢酶和磷脂-二酰甘油酰基转移酶。这些发现提示了旨在增强微藻中脂质产生的代谢工程的潜在目标。
结论：我们希望我们的发现将有助于理解碳浓缩机制，光合作用,氮同化，和根据CO2浓度的绿藻的脂质积累代谢。这项研究还为微藻的系统代谢工程提供了见解，以改善未来的性能。
