Natural pesticide for the production of protein-rich microalgae

In times of climate crisis and food shortages, the cultivation of microalgae is a promising solution that could fundamentally change the way we produce animal feed, bioplastics or biofuel. However, the enormous potential is still largely untapped, which is partly due to undeveloped cultivation methods. One of the challenges is to protect the cultures against pests. A new publication by Eawag now shows that co-cultures of different microalgae are more resistant to pests than monocultures.

For hundreds of years, people have been harvesting wild microscopic algae from lakes as a source of food. The Aztecs, for example, are known to have used fine nets to skim Spirulina from the surface of Lake Texcoco. They dried it and used it in a variety of foods.

To this day, microalgae are popular as a superfood as they contain antioxidants and omega-3 fatty acids, for example. Numerous beneficial health effects are attributed to them. However, the potential of the tiny algae goes far beyond their use in food supplements: microalgae could help to solve some of the most pressing problems of the modern world.

In their study, the researchers led by Thomas cultivated the algae species Nannochloropsis limnetica together with another microalgae, Botryococcus braunii. This species is commercially interesting due to its high content of hydrocarbons that can be used for biofuels, as well as valuable pigment compounds. B. braunii grows very slowly, but it does has another advantage: as the researchers discovered, co-cultures of Nannochloropsis and B. braunii are much more robust against the widespread herbivores Daphnia magna (a water flea about 2 mm in size) and Poterioochromonas malhamensis (a microscopic flagellate) than a monoculture of Nannochloropsis.

Both the biomass and the growth rate of the two algae were increased in the co-culture. Thomas explains: -On the one hand, we attribute this to the fact that B. braunii forms large colonies that are inedible to the herbivores, which can protect Nannochloropsis by reducing the efficiency of herbivores in capturing their algal prey. On the other hand, it is known to excrete compounds like free fatty acids, which are also likely to function as a defence mechanism.-

Positive interactions between the two types of algae could also play a role, adds Thomas. -With a co-culture, the complementary properties of the two algae species can be utilised.- Furthermore, a co-culture also enables the reduced use of pesticides, which have environmental risks and could lead to pesticide resistance in herbivorous pests. -We hope that our results will help to reduce the costs of growing microalgae and thus make large-scale cultivation more economically viable.-

Emphasising that, based on this proof-of-concept study, a great deal of additional research and practical pilot studies are needed to further explore and expand the concept, the researcher says that the next steps could be to transfer the concept to larger scales and to other species and different environments, such as saltwater-based ones.

Thomas, P. K.; Arn, F. J.; Freiermuth, M.; Narwani, A. (2024) Botryococcus braunii reduces algal grazing losses to Daphnia and Poterioochromonas through both chemical and physical interference, Journal of Applied Phycology , doi: 10.1007/s10811’024 -03330-x , Institutional Repository