Scientists develop high-CO2-tolerant super oleaginous microalgae

[China] The rapid elevation of atmospheric carbon dioxide level has led to global warming and ocean acidification. Microalgae, accounting for nearly 40% of global carbon dioxide fixation on Earth, are on the forefront of mankind’s battle against climate change, since many of them are able to directly convert sunlight and industrial carbon dioxide stream into transportation fuels and energy-rich nutrients.

However, the high concentration of carbon dioxide in flue gases would generally inhibit the growth of industrial microalgae. Therefore, reducing the so-called “CO2 poisoning effect”, i.e., improving the tolerance to high level of CO2, has become one priority in the development of super microalgae for carbon fixation.

In a new study published in Metabolic Engineering, a team of scientists led by Prof. XU Jian from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT), Chinese Academy of Sciences (CAS), and Prof. Ansgar Poetsch from Ruhr University, developed a way to improve the tolerance to high level of CO2 in the industrial oil-producing microalgae Nannochloropsis.

The research team started by discovering CA2, a key enzyme of the Carbon Concentrating Mechanism (CCM), as a key sensor of the extracellular CO2 level. Then instead of enhancing the function of the sensor, they reduced its activity by RNAi-based gene knockdown. Surprisingly, the mutants were able to grow 30% faster than the wild-type cells under the 5% CO2 level in flue gas, over 100 times higher than the 0.04% CO2 level found in the air. Moreover, this advantage was persistent under various types of photobioreactors and a wide range of cultivation scales.

In ancient times, the atmospheric CO2 level on Earth was many times higher than that of today. Over millions of years’ evolution, the CCMs of microalgae, whose role was to concentrate CO2 molecules around the prevalent carbon fixing machinery called RuBisCO, have had to gradually adapt to the lower and lower level of CO2 in the atmosphere.

Therefore, the research team, by down-regulating the CCM activity, essentially turned back the clock of this evolution process and returned the modern-day CCM to its ancient high-CO2-accustomed form. This “anti-evolution” endeavor by scientists improves the microalga’s tolerance to high CO2 environments, such as that found in flue gases.

This novel strategy has general implications to the development of industrial oil-producing microalgae as well as food crops, under circumstances where high carbon levels are beneficial or even necessary.

These circumstances can arise not only in the industrial conversion of flue gas for reducing carbon emission and mitigating global warm, but also in mankind’s space exploration hunting for next home. For example, in Mars, the most promising planet to serve as mankind’s second home due to its short distance to the Earth, the level of CO2 is as high as 95%. Thus changing this hostile atmosphere to a human-friendly one is a must before the Mars can be called home.

 

Photo: Mechanisms for the higher acidity tolerance in the CA2-knockdown N. oceanica. (Image by WEI Li)

View original article at: Scientists develop high-CO2-tolerant super oleaginous microalgae

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