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Browsing UB - Resumos em livros de actas by Author "Arneborg, Nils"
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- Antimicrobial peptides from Saccharomyces cerevisiae induce physiological changes in Hanseniaspora guilliermondiiPublication . Branco, Patricia; Albergaria, Helena; Arneborg, NilsSaccharomyces cerevisiae secretes antimicrobial peptides (AMPs) during alcoholic fermentation that are active against other wine-related yeasts (e.g. Hanseniaspora guilliermondii) (Albergaria et al., 2010) and bacteria (e.g. Oenococcus oeni) (Osborne and Edwards, 2007). In the present study we assessed the physiological changes induced by those AMPs on sensitive yeast cells of Hanseniaspora guilliermondii, namely membrane permeability and intracellular pH (pHi) alterations. Membrane permeability was evaluated by staining cells with propidium iodide (PI) and pHi by the fluorescence ratio imaging microscopy (FRIM) technique (Guldfeldt and Arneborg, 1998). Results showed that after 20 min of incubation with inhibitory concentrations of AMPs, the average pHi of cells dropped from 6.5 to 5.4. After 8 h of incubation, 32% of the cells had lost their ĢpH (=pHi-pHext) and after 24 h that percentage rose to 77%. The culturability (plating) and viability (PI staining) of the sensitive yeast cells also decreased in the presence of the AMPs. After 24 h of exposure to AMPs, 61% of the cells were dead (PI-stained) and the number of viable cells fell from 1 ~105 to 1.5 CFU/ml, which means that virtually all cells (99.999%) became unculturable but a sub-population of 39% of cells remained in a viable but non-culturable (VBNC) state. However, those VBNC cells were able to recover their culturability after incubation at optimal growth conditions. Our study revealed that the mode of action of these AMPs seems to be primarily targeted to the cell membranes, reducing their permeability and preventing cells to maintain pH homeostasis.
- Interactions between Saccharomyces cerevisiae and Hanseniaspora guilliermondii: cell-cell contact mechanismPublication . Branco, Patricia; Kemsawasd, Varongsiri; Arneborg, Nils; Albergaria, HelenaSeveral studies have shown that the early death of non-Saccharomyces during wine fermentations are due to yeast-yeast interactions induced by Saccharomyces cerevisiae (Sc) through different mechanisms such as growth arrest mediated by a cell-cell contact mechanism (Nissen et al. 2003) and death mediated by killer-like toxins (Pérez-Nevado et al 2006; Albergaria et al. 2010). Besides, previous work also showed that death of non-Saccharomyces in co-cultivation with Sc is always triggered at the end of exponential growth phase (Pérez-Nevado et al 2006). In order to investigate the role of cell-cell contact in the early death of non-Saccharomyces, we performed assays in which Sc cells pre-grown at enological growth conditions for 12 and 48 h, respectively, were in direct contact with Hanseniaspora guilliermondii (Hg) cells at high cellular density (107-108 cells/ml) in a carbon-free medium. As a negative control we performed similar assays in which Sc and Hg cells were separated by a dialysis tube (pore cut-off of 1000 kDa) and as a positive control a single Hg culture. Results showed that Hg cell density decreased by 2 orders of magnitude (i.e. from 108-106 cells/ml) in contact with 48 h-grown Sc cells, while its viability remained unchanged (108cfu/ml) in the presence of 12 h-grown Sc cells. Moreover, Hg viability was not affected both in the dialysis tube experiments and single culture, which confirmed the death-induced cell-cell contact phenomenon.