Pseudohyphae are chains of elongated budding yeast cells that remain attached after cell division. Unlike true hyphae, they exhibit constrictions at the septal junctions and individual cells retain distinct identity. This morphology represents an intermediate growth form between unicellular budding and filamentous hyphal growth and is characteristic of certain yeasts, most notably species of Candida.
Structural characteristics and formation
Pseudohyphal growth arises when budding yeasts continue to elongate rather than fully separate, causing daughter cells to remain attached to the mother cell. Each segment is separated by a constriction rather than the uniform tubular structure of a true hypha. Bud scars are visible at these constrictions, and the cell walls remain relatively thick. Environmental factors such as nutrient limitation, low nitrogen, serum exposure and temperature shifts can induce pseudohyphal differentiation in Candida albicans and related species. At the molecular level, signalling pathways involving Cdc28–Cln3, mitogen-activated protein kinases and cAMP–protein kinase A modulate the switch from yeast to pseudohyphal growth. This morphological plasticity allows yeasts to adapt to changing conditions and explore surfaces more effectively than simple budding.
Yeast morphogenesis and pathogenicity
In pathogenic yeasts such as C. albicans, pseudohyphae represent one stage in a complex morphogenetic programme that also includes true hyphae and round budding cells. The ability to transition between these forms is linked to virulence. Pseudohyphae can penetrate host tissues more effectively than budding cells and display altered cell wall composition that affects immune recognition. During mucosal candidiasis, the fungus often exhibits a mixture of yeast, pseudohyphal and hyphal forms. Nutrient deprivation, pH changes and interaction with host serum can trigger pseudohyphal growth, and loss of genes required for filamentation reduces virulence. The distinction between pseudohyphae and true hyphae is useful in clinical diagnostics because pseudohyphae show regular constrictions at septa, whereas hyphae maintain parallel walls with no narrowing at septal sites.
Pseudohyphae exemplify the morphological adaptability of yeasts and contribute to their survival in diverse niches. Recognising this form helps in diagnosing infections and understanding how pathogenic yeasts switch between unicellular and filamentous growth.
Related Terms: Yeast, Hypha, Candida albicans, Dimorphism, Biofilm