Oleaginous fungi, a special class of fungi with the ability to accumulate high levels of lipids (fats, 20% to 70% of their dry weight) within their cells, are gaining significant interest as a sustainable source of biofuels and nutraceuticals. These fungi offer several advantages over traditional sources of lipids, such as plants and animals. They can grow on various substrates or surfaces, including waste materials, and don’t require sunlight for growth. Additionally, oleaginous fungi can be cultivated in controlled environments, making them a reliable and consistent source of lipids. A research paper published in The Archives of Microbiology in June entitled Oleaginous fungi: a promising source of biofuels and nutraceuticals with enhanced lipid production strategies explored oleaginous fungi, their potential applications, and methods for detecting and enhancing lipid production.
Oleaginous fungi synthesize lipids through two main pathways: de novo biosynthesis and ex novo biosynthesis. In de novo biosynthesis, the fungus builds lipids from scratch using simple sugars. Ex novo biosynthesis involves breaking down complex lipids (like oils) from the fungi’s environment and using the components to create new lipids.
Researchers have developed various methods to determine the lipogenic potential (or lipid production ability) of oleaginous fungi. These methods can be categorized as qualitative and quantitative. Qualitative methods provide a quick and easy estimate of the lipid content but don’t offer precise measurements. Dyes like Nile red and Sudan Black B have a high affinity for lipids and are used as stains to observe the lipids under a microscope. This allows researchers to assess the presence and potential abundance of lipids in the fungi.
On the other hand, quantitative, or gravimetric methods provide an accurate measurement of the lipid content in a sample. Gravimetric analysis is the most common quantitative method. It involves extracting lipids from the fungi using solvents and then measuring the weight of the extracted lipids. This method is more complex and time-consuming than qualitative methods but offers valuable data for optimizing lipid production.
Scientists are actively researching ways to improve lipid production in oleaginous fungi. One of the key strategies outlined in the paper mentioned was growth condition optimization, where by optimizing outside abiotic factors such as the pH, salinity, and temperature of the growth medium, researchers can create ideal conditions for the fungi to accumulate lipids. They also applied biochemical engineering techniques by introducing the fungi to physiological stress, such as nutrient depletion (nitrogen, phosphorus, and sulfur), to force the fungi to metabolize in a way that favors lipid accumulation.
Another proven method for increasing production is co-culturing, where the oleaginous fungi are grown alongside other microorganisms like bacteria, algae, or different types of fungi. The organisms develop a mutually beneficial relationship, where each is triggered by the other’s presence to produce higher levels of certain metabolites. Research published in 2011 described how co-culturing the oleaginous yeast Rhodotorula glutinis with the microalga Chlorella vulgaris increased lipid production 3.8-fold, indicating that it may be a valuable source for biofuel.
Genetic engineering, where scientists can modify the genes of oleaginous fungi to increase their lipid production capacity, has also been explored. This approach uses metabolic engineering to prioritize certain enzymes or pathways in the fungi that enhance lipid production and block others so the energy usually used for their upkeep can be redirected to lipid production as well. This has the potential to create high-yielding strains of oleaginous microorganisms for large-scale production. Additionally, new extraction methods are being developed to extract lipids from the fungi in a way that maximizes yield and cost-effectiveness.
With improved methods of production and higher yields of lipids, researchers have begun to explore the various ways in which oleaginous fungi are valuable for different applications. Biofuel production is one such application, as the extracted lipids can be further converted into biodiesel, a renewable and environmentally friendly alternative to fossil fuels. The eco-friendly nature of oleaginous fungi makes this a particularly attractive option, as it is naturally fast-growing and not excessively technologically demanding as an organism, though more research needs to be done to make the extraction of lipids less expensive and accessible on a large scale.
Nutraceutical development is another area where fungal lipids can have great impact; they are rich in bioactive compounds such as essential fatty acids. Specifically, they are a valuable source of polyunsaturated fatty acids or PUFAs, which can’t be created by the human body and have to be eaten as part of our diets. While some types of PUFAs can be obtained through plants and fish, plants primarily only produce ALAs, or alpha-linolenic acids. While there are benefits to consuming ALAs, such as lowering inflammation and blood pressure, its main function is to convert to the more potent PUFAs, EPAs, and DHAs (eicosapentaenoic acids and docosahexaenoic acids). These are the far more effective omega-3 fatty acids, which help with brain, eye, and heart health.
However, the conversion rate from ALA to EPA and DHA is low, meaning plants alone cannot provide an adequate amount for human nutrition, and while fatty fish are a very good direct source of EPAs and DHAs, there are problems associated with using fish for that purpose, including overfishing, pollution of waters that affect the quality of the fish, and dietary restrictions of those who cannot consume fish oil. Oleaginous fungi are perfect for bridging that gap, as they contain adequate amounts of EPAs and DHAs, can be grown in controlled environments without overburdening natural resources, and can be used to produce vegan and vegetarian supplements.
As research continues to improve lipid production efficiency and explore new applications, oleaginous fungi are poised to play a significant role in a world that aims to move towards a more sustainable, environmentally conscious future.
