CELL-WALLS PROTEINS AND THEIR INVOLVEMENT IN THE FLOCCULATION OF PICHIA-STIPITIS

The concern of this work is related to flocculation in strains of Pich ia stipitis(D-xylose fermenting yeast). Investigations in this area en abled us to realize that, similar to other cell aggregation systems, p roteins play an important role in the phenomenon. The evidence that pr oteins are strongly involved in flocculation was corroborated by irrev ersible deflocculation caused by protease and by the reversible defloc culation caused by denaturating agents such as urea and sodium dodecyl sulphate (SDS). The results are discussed in the light of the basis o f protein chemistry. Through quantitative analysis, the protein conten t in the cell wall of flocculating and non-flocculating strains was fo und to be higher in the former than in the latter. The elemental analy sis also revealed a higher nitrogen content and a less phosphorus cont ent in the cell wall of flocculating strains than the corresponding ce ll walls of non-flocculating ones.