Repression and induction of flocculation interactions in Saccharomyces cerevisiae

Abstract

The biological control of flocculation interactions by factors related to growth under different conditions of aeration was documented with a new assay for flocculence. The degree of flocculence expressed in a genetically defined Saccharomyces cerevisiae strain (FLO1/FLO1 ade1/ade1) remained constant during aerobic growth but varied with aeration. Flocculence was repressed in anaerobically growing cells but was induced in stationary cells or cells returned to aerobic growth. Repression was correlated with the selective inactivation of cell surface lectin-like components. The changes in flocculence were accompanied by changes in 16 extractable proteins separated by electrophoresis; however, a clear correlation between specific protein bands and flocculence could not be established. The study clearly demonstrated that the phenotypic expression of FLO1 could be reproducibly manipulated for experimental purposes by aeration alone.

Identification of a 49-kDa hydrophobic cell wall mannoprotein present in velum yeast which may be implicated in velum formation

“…In the £occulation process, although the formation of aggregates is mediated via interactions between the lectinlike protein and mannose chain [18], hydrophobic interactions are generally considered to have an important role in cell aggregates and velum formation. Taking into account the importance of CSH in velum formation [5^8], it is likely that this mannoprotein (which is the only component which allows us to distinguish between yeast able and unable to form a velum) is involved in velum formation.…”

A Method To Disperse Aggregates of a Flocculent Yeast for Photometric Analysis

“…Environmental parameters such as cell density, pH, temperature, light, aeration, agitation, ionic strength, carbon source, and nutrients present in the medium, etc., all play a significant role. For example, the degree of flocculation can vary with the degree of aeration (7,10). Higher temperatures can be used to deflocculate a culture (14).…”

“…The kind of sugar used as a carbon source affects the degree of flocculation (6,8,9). The composition of the growth medium can also influence the degree of flocculation (2,3,6,7,9,12). Accumulation of metabolic products like ethanol can induce the cells to flocculate as a response to the ethanol built up inside the cells ( 4 ) .…”

“…The floc formation has been explained in many ways with no clear consensus. Proteins are considered essential for floc formation (6,7,(10)(11)(12). The Ca2+ ions have been considered as activators of a component found only on flocculent yeasts that binds to the mannan layer of the cells, allowing the interaction between them (6).…”

Characterization of non-flocculent cells isolated from a culture of flocculent Saccharomyces cerevisiae NCYC 1001

“…Although the mechanism of flocculation has not been characterised in detail, three hypotheses have been advanced to describe the process. These are (i) a lectin-like binding between a protein and cell wall mannan [4,5,10,11], (ii) cross bridging of anionic functional groups on adjacent cell surfaces by divalent cations such as calcium [12,13] and (iii) neutralization of the surface charge [14,15].…”