Chlorella ohadii, a type of green algae considered to be the fastest-growing plant cell, is one of 13 species of single-celled green algae that have been considered as a source of food and energy because its photosynthetic efficiency can reach eight percent, which exceeds that of other highly efficient crops such as sugar cane.

Chlorella is a food source because it is high in protein and other essential nutrients; when dried, it is about 45% protein, 20% fat, 20% carbohydrate, and 10% minerals and vitamins and five percent fiber. Mass-production methods are now being used to cultivate it in large man-made circular ponds. It is commonly used as a superfood and can be found as an ingredient in certain liquid-based cocktails.

In ideal conditions, cells of Chlorella multiply rapidly, requiring only carbon dioxide, water, sunlight, and a small number of minerals to reproduce. 

The name Chlorella is taken from the Greek word meaning green, and the Latin suffix ella, meaning small. The German biochemist and  cell physiologist Otto Heinrich Warburg, who was awarded the Nobel Prize in Physiology or Medicine in 1931 for his research on cell respiration, also studied photosynthesis in Chlorella. In the process of photosynthesis, plants and algae convert water, light, and carbon dioxide into the sugar and oxygen essential for their functioning. 

In 1961, Melvin Calvin of the University of California received the Nobel Prize in Chemistry for his research on the pathways of carbon dioxide assimilation in plants using Chlorella.

Over the years, experimental research was carried out in laboratories rather than in the field – and scientists discovered that Chlorella would be much more difficult to produce than previously thought. To be practical, the algae grown would have to be placed either in artificial light or in shade to produce at its maximum photosynthetic efficiency. 

Also, for the Chlorella to be as productive as the world would require, it would have to be grown in carbonated water, which would have added millions to the production cost. A sophisticated process, and additional cost, was required to harvest the crop, and, for Chlorella to be a viable food source, its cell walls would have to be pulverized. The plant could reach its nutritional potential only in highly modified artificial situations. 

Although the production of Chlorella looked promising and involved creative technology, it has not to date been cultivated on the scale some had predicted. Costs have remained high, and Chlorella has for the most part been sold as a dietary supplement, for cosmetics, or as animal feed. 

Chlorella ohadii, which is isolated from biological desert soil crusts, thrives under extreme high light and is highly resistant to photoinhibition – the phenomenon of a decrease in photosynthesis shown by plants when they are exposed to a lot of sunshine. This alga is known for its ability to survive in extreme conditions of heat and cold, which forces it to exhibit resilience and grow very quickly.

Now, researchers at the Max Planck Institute for Molecular Plant Physiology in Germany and at Tel Aviv University (TAU) have cracked the mechanism of photosynthesis in this fastest-growing alga on earth.  

They believe that their work will lead to speeding up future developments in engineering in the field of algae-based sustainable food as a genetic reservoir for plant improvement and feeding a hungry world

The study, led by findings indicates that the main factors behind the plant’s rapid photosynthesis rate lie in its efficient metabolic processes. The researchers found that this alga has a unique ability to elicit a chemical reaction in which it is able to efficiently and quickly recycle one of the components used by an enzyme called RuBisCO in a way that significantly speeds up the photosynthetic processes. 

The study, led by Dr. Haim Treves, a member of TAU’s School of Plant Sciences and Food Security who also works at the German institute,  was published in the prestigious journal Nature Plants under the title “Carbon flux through photosynthesis and central carbon metabolism show distinct patterns between algae, C3, and C4 plants.” 

The team wanted to know if it was possible to improve the efficiency of photosynthesis in plants – an energetic process that has been occurring in nature for about 3.5 billion years. They decided to focus on green algae, particularly the Chlorella ohadii variety. 

The researchers assessed that a better understanding of Chlorella ohadii (named after the late Hebrew University of Jerusalem botanist Prof. Itzhak Ohad) would make it possible to improve the efficiency of photosynthesis in other plants as well, and in turn to develop new engineering tools that could provide a solution for sustainable food.

The researchers used innovative microfluidic methods based on complex physical, chemical, and biotechnological principles in order to provide the algae with carbon dioxide in a measured and controlled manner and monitor the photosynthesis “online.”

By using comparative analysis, the researchers identified that there was a fundamental difference in the photosynthetic processes carried out in in green algae compared to the model plants. They assess that the difference lies in variations in the metabolic networks, a deeper understanding of which will help in developing innovative engineering solutions in the field of plant metabolism, as well as the optimal engineering of future agricultural products.

“Past empirical studies have shown that photosynthetic efficiency is higher in microalgae than in C3 or C4 crops, both types of plants that have transport systems but which are completely different in terms of their anatomy and the way they carry out photosynthesis,” noted Treves. “The problem is that the scientific community does not yet know how to explain these differences accurately enough.”

“In our current study, we mapped the patterns of energy production and photosynthetic metabolism in green algae and compared them to existing and new data collected from model plants. We were able to clearly identify the factors that influence the difference in these patterns. Our research reinforces previous assessments that the metabolic pathway responsible for recycling is one of the major bottlenecks in photosynthesis in plants. The next step is to export the genes involved in this pathway and in other pathways in which we have detected differences from algae, and to test whether their insertion into other plants via metabolic engineering will increase their rate of growth or photosynthetic efficiency,” he continued.