In summary, we have shown that the yeast flocculin Flo11p, one of the most intensively studied microbial adhesion molecules, is shed from cells. This discovery challenges the prevailing dogma for the regulation of microbial adhesion glycoproteins and their adhesive properties, including their roles in cell-surface variability and interactions with the cell wall/cell surface. Shed Flo11p may prevent cell adhesion in two ways: 1) the release of Flo11p from cells directly attenuates adherence, and 2) shed Flo11p binds to surfaces and may compete with cell-associated Flo11p for surface sites. As a result of the calibration of Flo11p’s adherence properties, cells maintain a balance that is optimal for the different foraging behaviors in which Flo11p is required.
We also show that multicellular communities of yeast secrete a fluid rich in shed mucins that may be functionally analogous to the mucus secretions produced by gastropods and other metazoans. Mucus production in microbes has implications in mucin evolution, fungal pathogenesis, and social evolution, in that production of a secreted material by individual cells can benefit the entire community [26
]. Glycoprotein shedding may contribute to the formation or regulation of an extracellular matrix-like material that along with other proteins [27
] may regulate biofilm expansion and architecture.
Mucin-like glycoproteins may be shed from pathogens and have unappreciated roles in virulence. Shed mucins would be among the first molecules encountered by the host, and their anti-adhesion properties may prevent host cells from attaching to the fungal surface. Detection of shed fungal glycoproteins may allow early diagnosis of pathogenic infections. Shedding of mucin glycoproteins adds to the repertoire of surface variability [7
] by contributing to cell-surface variation and by generating complex, non-uniform collections of cells with varying adherence properties. Mucin shedding in microbes may not be limited to fungi: the protozoal parasite Trypanosoma cruzi
express as many as 850 different mucin-coding genes [29
], and it is tempting to speculate that mucin shedding in eukaryotic pathogens is tailored to optimize virulence.