Genetically controlled self-aggregation of cell-surface-engineered yeast responding to glucose concentration

We constructed an arming (cell-surface-engineered) yeast displaying two typ es of agglutinin (modified a-agglutinin and alpha -agglutinin) on the cell surface, with agglutination being independent of both mating type and phero mones. The modified a-agglutinin was artificially prepared by the fusion of the genes encoding Aga1p and Aga2p. The modified a-agglutinin could induce agglutination of cells displaying Ag alpha 1p (alpha -agglutinin). The ups tream region of the isocitrate lyase gene of Candida tropicalis (UPR-ICL), active at a low glucose concentration, was used as the promoter to express the modified a-agglutinin- and alpha -agglutinin-encoding genes. The arming yeast displaying both agglutinins agglutinated and sedimented in response to decreased glucose concentration. When the glucose concentration was high , the arming yeast grew normally, In the late log phase, when the glucose c oncentration became very low, agglutination occurred suddenly and drastical ly and yeast cells sedimented completely. Sedimentation was confirmed by we ighing the aggregated cells after filtration of the broth, Strains in which aggregation can be genetically controlled can be used in industrial proces ses in which the separation of yeast cells from the supernatant is necessar y.