The most important dogma in white-wine production is the preservation of the wine aroma and the limitation of the oxidative action of oxygen. In contrast, the aging of Sherry and Sherry-like wines is an aerobic process that depends on the oxidative activity of flor strains of Saccharomyces cerevisiae. Under depletion of nitrogen and fermentable carbon sources, these yeast produce aggregates of floating cells and form an air–liquid biofilm on the wine surface, which is also known as velum or flor. This behavior is due to genetic and metabolic peculiarities that differentiate flor yeast from other wine yeast. This review will focus first on the most updated data obtained through the analysis of flor yeast with -omic tools. Comparative genomics, proteomics, and metabolomics of flor and wine yeast strains are shedding new light on several features of these special yeast, and in particular, they have revealed the extent of proteome remodeling imposed by the biofilm life-style. Finally, new insights in terms of promotion and inhibition of biofilm formation through small molecules, amino acids, and di/tri-peptides, and novel possibilities for the exploitation of biofilm immobilization within a fungal hyphae framework, will be discussed.

Flor yeasts of Saccharomyces cerevisiae have an innate diversity of FLO11 which codes for a highly hydrophobic and anionic cell-wall glycoprotein with a fundamental role in biofilm formation. In this study, 380 nitrogen compounds were administered to three S. cerevisiae flor strains handling FLO11 alleles with different expression levels. S. cerevisiae strain S288c was used as the reference strain as it cannot produce FLO11p. The flor strains generally metabolized amino acids and dipeptides as the sole nitrogen source, although with some exceptions regarding L-histidine and histidine containing dipeptides. L-histidine completely inhibited growth and its effect on viability was inversely related to FLO11 expression. Accordingly, L-histidine did not affect the viability of the Δflo11 and S288c strains. Also, L-histidine dramatically decreased air–liquid biofilm formation and adhesion to polystyrene of the flor yeasts with no effect on the transcription level of the FLO11 gene. Moreover, L-histidine modified the chitin and glycans content on the cell-wall of flor yeasts. These findings reveal a novel biological activity of L-histidine in controlling the multicellular behavior of yeasts.

Street food is a prevalent part of the food service industry. It is convenient in terms of accessibility and cost, but perceived as potential risk of foodborne illness. Accordingly, the safety of street foods in Beirut, Lebanon was assessed using an observational checklist and microbiological analyses. A total of 30 vendors were observed for their food safety parameters and 60 samples were analyzed for their content of Escherichia coli, Staphylococcus aureus, Listeria spp., and Salmonella spp., then, statistical analyses were performed for possible correlations. Results showed unsatisfactory levels of foodborne pathogens. Microbiological contamination was significantly correlated to unproper environmnental surroundings, deficiency of potable water, money handling, inappropriate methods of refrigeration, and the limited access to improper disposal facilities near stalls. These findings reveal the microbiological quality of street foods served in Beirut, and highlight on the practices to be ameliorated to provide safe street food products to consumers. Practical applicationsStreet food emerges as a social adaptation in urban areas due to its rapid lifestyle hence it may present a public health risk due to various factors. The current study is the first of its kind to be conducted in Beirut and its results present solid basis for further practices at different levels.Divulgation of its results would lead to new governmental laws to protect the public health and reduce the economic burdens related to hospitalization due to foodborne pathogens and poisoning. Educational institutions would also be involved in applications related to training and awareness sessions for street food handlers, to teach them the good hygienic practices. This study will also help consumers identify good and bad hygienic practices thus choose appropriate street food handlers.

bSaccharomyces cerevisiae "flor" yeasts have the ability to form a buoyant biofilm at the air-liquid interface of wine. The formation of biofilm, also called velum, depends on FLO11 gene length and expression. FLO11 encodes a cell wall mucin-like glycoprotein with a highly O-glycosylated central domain and an N-terminal domain that mediates homotypic adhesion between cells. In the present study, we tested previously known antimicrobial peptides with different mechanisms of antimicrobial action for their effect on the viability and ability to form biofilm of S. cerevisiae flor strains. We found that PAF26, a synthetic tryptophanrich cationic hexapeptide that belongs to the class of antimicrobial peptides with cell-penetrating properties, but not other antimicrobial peptides, enhanced biofilm formation without affecting cell viability in ethanol-rich medium. The PAF26 biofilm enhancement required a functional FLO11 but was not accompanied by increased FLO11 expression. Moreover, fluorescence microscopy and flow cytometry analyses showed that the PAF26 peptide binds flor yeast cells and that a flo11 gene knockout mutant lost the ability to bind PAF26 but not P113, a different cell-penetrating antifungal peptide, demonstrating that the FLO11 gene is selectively involved in the interaction of PAF26 with cells. Taken together, our data suggest that the cationic and hydrophobic PAF26 hexapeptide interacts with the hydrophobic and negatively charged cell wall, favoring Flo11p-mediated cell-tocell adhesion and thus increasing biofilm biomass formation. The results are consistent with previous data that point to glycosylated mucin-like proteins at the fungal cell wall as potential interacting partners for antifungal peptides.