HMN 2025: How Increase in cell volume and nuclear number of the koji fungus enhances enzyme production capacity

Researchers at University of Tsukuba have identified key characteristics underlying the high enzyme production capacity of the koji fungus Aspergillus oryzae.

The koji fungus Aspergillus oryzae has long been used in traditional Japanese brewing and fermentation for sake, soy sauce, and miso. Today, it is also widely used in the bioindustry as a host for enzyme production.

The study, published in the journal eLife, reveals cellular traits of A. oryzae linked to enzyme production through cell biological analysis. The authors found that, over time in culture, hyphae thicken, resulting in a 10-fold increase in cell volume.

Simultaneously, the number of nuclei per hyphal cell also rises 10-fold, exceeding 200. This increase in cell volume and nuclear number is unique among the Aspergillus species studied and correlates with the fungus’s high enzyme production capacity.

As nuclear number and cell volume are interrelated, both must increase concurrently. The researchers also identified genetic factors involved in each of these changes. Such traits require high energy and are unlikely to be selected in natural environments.

However, A. oryzae, bred over centuries in nutrient-rich environments, may have acquired this trait through artificial selection. Similarly, increased cell volume and nuclear number were also observed in industrial strains of Trichoderma and Penicillium used for enzyme production.

These findings offer fundamental insights into how cell volume and nuclear number are regulated in multinucleate organisms and provide new directions for breeding filamentous fungi for industrial use.

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