A fungus already used in food fermentation could become a more versatile ingredient for meat alternatives. Researchers used CRISPR-based engineering to change what Aspergillus oryzae produces, creating fungal biomass with more ergothioneine or more heme—the iron-containing molecule associated with the colour of red meat.
The study in Nature Communications, led by Vayu Maini Rekdal and colleagues, demonstrated changes in composition and appearance. Whether people would prefer the taste of these engineered foods remained an open question.
A toolkit for changing a food fungus
The ingredient is mycelium: the network of microscopic filaments that makes up much of a fungus. Those filaments give the harvested biomass a fibrous structure, making it interesting as a food material in its own right.
To adjust its properties, the team developed a modular toolkit for inserting genes and controlling their expression in A. oryzae. It combined CRISPR-Cas9 with selected genomic insertion sites and promoters—the DNA sequences that help regulate how strongly genes are expressed.
The researchers identified sites that could accommodate gene insertions without a detectable growth penalty in their tests. That offers a more controlled starting point than inserting genes at unpredictable positions. It does not mean that every future modification at those sites will be harmless or suitable for food.
More ergothioneine, with a growth trade-off
One set of strains targeted ergothioneine, a compound found in mushrooms that has antioxidant properties. The team increased expression of two candidate genes from the fungus’s own genome, AO_Egt1 and AO_Egt2, involved in its biosynthesis.
The two engineering arrangements increased ergothioneine levels approximately 11-fold and 21-fold relative to the background strain. The higher-producing strain averaged about 1.5 times the level measured in the oyster mushroom comparison, on a dry-weight basis.
However, the ergothioneine-producing strains also showed a small growth disadvantage under the tested conditions. The result illustrates an engineering trade-off: directing more resources towards a useful compound can affect growth. A higher concentration in fungal biomass also does not, by itself, establish a health benefit from eating it.
Heme changes the colour
A separate strain targeted heme production. The researchers altered the expression of several heme-pathway enzymes and introduced soy leghemoglobin, a protein that binds heme.
This strain contained about four times as much heme as the background strain, measured on a dry-weight basis. Its biomass appeared redder, and the colour difference remained after the material was formed into patties and cooked. The study reported no reduction in growth yield or protein content for this heme-engineered strain under the conditions examined.
These are distinct experimental results. The high-ergothioneine strain and the heme-enriched strain should not be described as one finished product that demonstrated all the benefits together.
From a prototype to something people would eat
The work shows that a food fungus’s molecular composition and appearance can be adjusted through enzyme-pathway engineering. It does not establish that the prototypes taste better, improve human health or have a lower environmental footprint than existing foods.
The authors explicitly identify sensory testing, consumer acceptance, food safety and regulatory assessment as further steps. Fungal food is also a more accurate description here than plant-based food: fungi are not plants.
The paper discloses that Maini Rekdal and Jay Keasling are inventors on a related provisional patent, and that Keasling has financial interests in several biotechnology companies.
For another food application with directly measured performance, read our report on an engineered enzyme tested in bread.
Source
Maini Rekdal, V. et al. (2024). Edible mycelium bioengineered for enhanced nutritional value and sensory appeal using a modular synthetic biology toolkit. Nature Communications, 15, 2099. Read the study. The source is published under CC BY 4.0; this article is an independently written summary.
Update note: This archived report retains its original publication date and URL. The revision separates measured composition and colour changes from untested taste, health and environmental benefits.
