Under liquid culture conditions, the hyphae of filamentous fungi aggregate to form pellets, which reduces cell density and fermentation productivity. Previously, we found that loss of α-1,3-glucan in the cell wall of the fungus Aspergillus nidulans increased hyphal dispersion. Therefore, here we constructed a mutant of the industrial fungus A. oryzae in which the three genes encoding α-1,3-glucan synthase were disrupted (tripleΔ). Although the hyphae of the tripleΔ mutant were not fully dispersed, the mutant strain did form smaller pellets than the wild-type strain. We next examined enzyme productivity under liquid culture conditions by transforming the cutinase-encoding gene cutL1 into A. oryzae wild-type and the tripleΔ mutant (i.e. wild-type-cutL1, tripleΔ-cutL1). A. oryzae tripleΔ-cutL1 formed smaller hyphal pellets and showed both greater biomass and increased CutL1 productivity compared with wild-type-cutL1, which might be attributable to a decrease in the number of tripleΔ-cutL1 cells under anaerobic conditions.

Signal transduction pathways regulating cell wall integrity (CWI) in filamentous fungi have been studied taking into account findings in budding yeast, and much knowledge has been accumulated in recent years. Given that the cell wall is essential for viability in fungi, its architecture has been analyzed in relation to virulence, especially in filamentous fungal pathogens of plants and humans. Although research on CWI signaling in individual fungal species has progressed, an integrated understanding of CWI signaling in diverse fungi has not yet been achieved. For example, the variety of sensor proteins and their functional differences among different fungal species have been described, but the understanding of their general and species-specific biological functions is limited. Our long-term research interest is CWI signaling in filamentous fungi. Here, we outline CWI signaling in these fungi, from sensor proteins required for the recognition of environmental changes to the regulation of cell wall polysaccharide synthesis genes. We discuss the similarities and differences between the functions of CWI signaling factors in filamentous fungi and in budding yeast. We also describe the latest findings on industrial applications, including those derived from studies on CWI signaling: the development of antifungal agents and the development of highly productive strains of filamentous fungi with modified cell surface characteristics by controlling cell wall biogenesis.

Filamentous fungi generally form hyphal pellets in liquid culture. This property prevents filamentous fungi to apply the methods used for unicellular organisms such as yeast and bacteria.

Fungal-type galactomannan is a polysaccharide incorporated into the cell wall of filamentous fungi belonging to the subphylum Pezizomycotina. Biosynthetic enzymes of fungal-type galactomannan are potential targets for antifungal drugs and agrochemicals.

The anti-HIV drug nelfinavir suppresses the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in vitro . However, its efficacy in patients with COVID-19 has not been studied.