Effect of saccharomycin, a natural Saccharomyces cerevisiae biocide, on Hanseniaspora guilliermondii cells surface

INTRODUCTION: During spontaneous wine fermentations, most of the non-Saccharomyces yeasts present in grape musts show an early decline in their population. It was traditionally assumed that Saccharomyces cerevisiae (S.c.) prevalence was due to the higher resistance of this species to ethanol. However, wine fermentations performed with single cultures of non-Saccharomyces strains showed that those strains could withstand much higher ethanol levels [1]. It was then found that S.c. (strain CCMI 885) produced antimicrobial peptides (AMPs) that are responsible for the early death of the non-Saccharomyces yeasts [2]. In previous work, we isolated, purified and sequenced those ntimicrobial peptides (AMPs) and found that they derive from the glyceraldehyde 3-phosphate dehydrogenase enzyme [3]. These GAPDH-derived AMPs compose the natural biocide secreted by S.c., which we named saccharomycin, and are effective against sensitive yeasts both in its natural/isolated and synthetic form [4,5]. MATERIALS AND METHODS: Hanseniaspora guilliermondii (H.g.) were grown from 8 to 48 h in YEPD, centrifuged and washed (ethanol 3% or 6%) prior to incubation with natural the S.c. AMPs, at 25 °C for 1 or 2 h. Surface of H.g. cells were observed by Atomic Force Microscopy (AFM). RESULTS: AFM images of H.g. cells before and after (Figure 1) exposure to the AMPs show a significant changes on their surface. CONCLUSIONS AND DISCUSSION: Analysis of the cell's roughness, reveals that untreated cells are smooth, unlike the treated with AMPs. Cell´s surface roughness increased upon AMPs contact by about 50% from 40.31(±12.87) nm to 58.01(±13.97) nm. Surface morphological details also indicates a destructive effect of saccharomycin on the H.g. cell wall.