THE IONIC CHARACTER OF THE ENVIRONMENT IN THE FLOCCULATION OF PICHIA-STIPITIS

Although cells of a flocculation strains of Pichia stipitis became com pletely dispersed by washes in distilled water, they reflocculated whe n suspended in solutions of individual medium components. Ionic streng th was suspected to be the primary cause behind flocculation. The meas urement of the electrical conductivity showed to be a practical way of evaluating the ionic strength of the environment. Accordingly, floccu lation was more intense as the electrical conductivity of the aforemen tioned solutions increased. At higher values of electrical conductivit y (> 1000 muS) the degree of flocculation was nearly constant, suggest ing that charge reduction associated with conformational changes in ce ll wall proteins may be responsible for cell aggregation. Additionally , a decrease in electrical conductivity of the medium, through dialysi s, reduced the ability of the cells to flocculate. The ionic character of the medium showed to be an important influencing factor in floccul ation.