INFORM January 2024

20 • inform January 2024, Vol. 35 (1)

Oleaginous fungi Panagiotis Dritsas

In early 2019, a group of scientists discovered fungal hyphae and spores in a fossil collected from the Arctic Canadian shales that dated back over one billion years ago (https://doi.org/10.1038/ s41586-019-1217-0). Hence, the kingdom fungi had roots on Earth long before humans and likely served a vital role in the evolution of life along the way.

It is well-established that the first plants to emerge onto land formed intimate partnerships with fungi 500 million years ago. Specifically, fungi could secrete organic acids to dissolve rocks and extract nutrients such as trace elements and minerals which were supplied to the plants. In return, plants transferred nutrients produced through photosynthesis to the fungi. Their collaboration led to the worldwide spread of plants, affecting the composition of the atmosphere. Later, some single-celled fungi like yeasts brought bread and beer into daily life, making a key contribution to the creation of the first communities. Other fungi like Penicillium were the springboard to creating antibiotics and our current, high-quality standard of living. Today, about 144,000 species of fungi have been identified and described, albeit mycologists estimate that up to 4 million total species exist. While the question of what other mysteries remain regarding their impact on everyday life, we can report with certainty that a specific group of them, called oleaginous fungi, has the potential to offer feasible solutions to various industrial applications. WHY INVEST IN OLEAGINOUS FUNGI Oleaginous fungi exhibit the ability to accumulate triacylglycerols, named sin gle-celled oils (SCO), to up to 80% of their dry weight (Figure 1). SCO that contain polyunsaturated fatty acids (PUFA) have beneficial effects on health due to their anti-microbial, anti-viral and anti-cancer properties. More saturated lipids have appli cation in the biofuels industry as first- and second-generation biodiesel. Even though the ability of microorganisms to store energy in the form of neutral lipids has been known for over a century, oleaginous microorganisms have attracted the attention of research and industry only within the past few decades. Thus, any attempt to understand the process of lipid accumulation in the oleaginous species is relatively new to the field of research. Generally, lipogenesis is a secondary metabolic activity, strongly affected by the amount and type of carbon and nitrogen sources in the growth medium as well as by temperature, pH, dissolved oxygen, even the fermentation process (batch culture, fed-batch culture, or continuous culture). A key criterion for the use of a fungus for oil production at large scale is the quantity and the quality of the produced oil, in com bination with the possibility of using cheap raw material as a substrate. The ability of oleaginous fungi to grow and digest a wide variety of substrates, like glycerol or olive mill wastewaters, and to bio-transform them into products of high-added value (SCO, organic acids, proteins, enzymes) is of obvious research and industrial interest. GROWN ON RAW MATERIALS Glucose is the most common carbon source used by microorganisms and multiple studies have confirmed fungi can accumulate lipids in significant quantities when

• Some fungi produce lipids in high quantities that have a beneficial effect on health or can be channeled to biofuels industry. • Recently, lignocellulose and agro-industrial waste have been widely used as feedstock for oleaginous fungi with promising results. • Genetic manipulation on oleaginous yeast have expanded their use to more industrial applications. • Consortia of fungi and microalgae can lead to increased production of biomass and lipids, a feature of most importance for aquaculture and industry.