Identification of a Saccharomyces cerevisiae factor inducing flocculation of Pediococcus damnosus
1997
Bremt, K. van den | Nuyens, F. | Iserentant, D. | Verachtert, H. (Katholieke Univ. Leuven, Heverlee (Belgium). Lab. of Industrial Microbiology and Biochemistry)
Although mixed microbial interactions, especially yeast-bacterium interactions, play an important role in food fermentations, such as beer, kefir and sourdough production, little has been published on the mechanism of interaction between yeasts and bacteria. Lievens et al. (1994) found that coflocculation between Pediococcus damnosus and Saccharomyces cerevisiae was mediated by a lectin mechanism. The yeast cell wall protein responsible for coflocculation is also able to induce flocculation of P. damnosus cells. Isolation of this factor from the culture supernatant of S. cerevisiae has now been achieved, after concentrating the crude factor with a methanol precipitation, using ultrafiltration through a membrane with a 50,000 dalton cut off. Characterization of the pure factor showed that it is a hyper glycosylated mannoprotein. Amino acid analysis of the intact factor molecule could not be obtained because the factor was amino terminally blocked. Internal amino acid sequencing was performed after HPLC separation of different fragments of the factor obtained with a trypsin digest. Results indicate that the EXG1 gene, coding for an exo-beta(1,3)-glucanase, is the best candidate to the flocculation inducing factor. Testing the flocculation inducing activity of a EXG1 overexpressing yeast strain and a EXG1 deficient yeast strain, will enable us to test this hypothesis.
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