High intraspecific variation of the cell surface physico-chemical and bioadhesion properties in Brettanomyces bruxellensis

Flocculation Mechanisms in Brettanomyces bruxellensis: Influence of ethanol and sulfur dioxide on FLO gene expression

The mechanisms underlying flocculation in Brettanomyces bruxellensis, unlike the well-characterized FLO-family gene regulation in Saccharomyces cerevisiae, remain largely unexplored. This study investigates the flocculant phenotypes of 99 B. bruxellensis strains, revealing that only a minority exhibits this clumping behavior and confirms its strain-dependent attitude. Focusing on two strains, CBS2499 (flocculant) and UMY321 (non-flocculant), genetic analysis uncovered polymorphisms and distinct allelic heterozygosity in the FLO1 and FLO11 genes, potentially linked to the phenotypic differences. To further examine these traits, Response Surface Methodology (RSM) was used to simulate oenological conditions, testing the impact of pH, ethanol, and sulfur dioxide (SO₂) levels on flocculation and gene expression. The findings revealed that environmental stressors, especially ethanol and SO₂, significantly increase the expression of FLO1 and FLO11 in CBS2499, indicating a regulatory role in flocculation under stress. These insights broaden our understanding of stress adaptation in B. bruxellensis, especially its survival strategies in wine environments. By elucidating factors influencing flocculation, this study contributes valuable knowledge for managing B. bruxellensis spoilage, potentially aiding in the development of targeted approaches to reduce its impact on wine quality.

Does Fungal Chitosan Leave Noticeable Traces in Treated Wines?

Background (1): The use of fungal chitosan as an antiseptic in wine appears as a promising alternative to sulfur dioxide for the elimination of Brettanomyces bruxellensis sensitive strains. Nevertheless, its utilization raises the question, "how are the treated wines different from the untreated ones?" Methods (2): Chitosan treatment residues were sought in the oligosaccharide and polysaccharide fractions and among 224 low MW ions (<1800 g·mol-1) in several wines by using liquid chromatography (size exclusion HPLC or LC-MS) and GC-MS. Standard oenological parameters were also examined as well as possible sensory modifications by a panel of tasters composed of experts and non-experts. Results (3): None of these methods enabled the reproducible and reliable identification of a treated wine without comparing it to its untreated control. The fingerprints of treatment are not reliably detectable by the analytical methods used in this study. However, the treated wines seem permanently protected against the development of chitosan-sensitive strains of B. bruxellensis. Conclusions (4): If chitosan treatment modifies the wine, the associated changes were not identified by the liquid chromatography method mentioned above and they were not perceived by most people in our taster panel. However, the expected antimicrobial action of chitosan was observed on B. bruxellensis sensitive strains and persisted at least one year. Tolerant strains were less affected by these persistent effects.

Effect of abiotic and biotic factors on Brettanomyces bruxellensis bioadhesion properties

Biofilms are central to microbial life because of the advantage that this mode of life provides, whereas the planktonic form is considered to be transient in the environment. During the winemaking process, grape must and wines host a wide diversity of microorganisms able to grow in biofilm. This is the case of Brettanomyces bruxellensis considered the most harmful spoilage yeast, due to its negative sensory effect on wine and its ability to colonise stressful environments. In this study, the effect of different biotic and abiotic factors on the bioadhesion and biofilm formation capacities of B. bruxellensis was analyzed. Ethanol concentration and pH had negligible effect on yeast surface properties, pseudohyphal cell formation or bioadhesion, while the strain and genetic group factors strongly modulated the phenotypes studied. From a biotic point of view, the presence of two different strains of B. bruxellensis did not lead to a synergistic effect. A competition between the strains was rather observed during biofilm formation which seemed to be driven by the strain with the highest bioadhesion capacity. Finally, the presence of wine bacteria reduced the bioadhesion of B. bruxellensis. Due to biofilm formation, O. oeni cells were observed attached to B. bruxellensis as well as extracellular matrix on the surface of the cells.

Yeast biofilms on abiotic surfaces: Adhesion factors and control methods

Biofilms are highly resistant to antimicrobials and are a common problem in many industries, including pharmaceutical, food and beverage. Yeast biofilms can be formed by various yeast species, including Candida albicans, Saccharomyces cerevisiae, and Cryptococcus neoformans. Yeast biofilm formation is a complex process that involves several stages, including reversible adhesion, followed by irreversible adhesion, colonization, exopolysaccharide matrix formation, maturation and dispersion. Intercellular communication in yeast biofilms (quorum-sensing mechanism), environmental factors (pH, temperature, composition of the culture medium), and physicochemical factors (hydrophobicity, Lifshitz-van der Waals and Lewis acid-base properties, and electrostatic interactions) are essential to the adhesion process. Studies on the adhesion of yeast to abiotic surfaces such as stainless steel, wood, plastic polymers, and glass are still scarce, representing a gap in the field. The biofilm control formation can be a challenging task for food industry. However, some strategies can help to reduce biofilm formation, such as good hygiene practices, including regular cleaning and disinfection of surfaces. The use of antimicrobials and alternative methods to remove the yeast biofilms may also be helpful to ensure food safety. Furthermore, physical control measures such as biosensors and advanced identification techniques are promising for yeast biofilms control. However, there is a gap in understanding why some yeast strains are more tolerant or resistant to sanitization methods. A better understanding of tolerance and resistance mechanisms can help researchers and industry professionals to develop more effective and targeted sanitization strategies to prevent bacterial contamination and ensure product quality. This review aimed to identify the most important information about yeast biofilms in the food industry, followed by the removal of these biofilms by antimicrobial agents. In addition, the review summarizes the alternative sanitizing methods and future perspectives for controlling yeast biofilm formation by biosensors.