Aims
Cells limit the cell number of dense biofilms by releasing self‐inhibitory molecules. Here, we aim to assess the effectiveness of yeast quorum sensing (QS) molecules and the antifungal agent natamycin against yeast biofilms of strains commonly isolated from fruit juice ultrafiltration membranes.
Methods and Results
Yeast QS molecules, such as tyrosol, 2‐phenylethanol and farnesol, were detected by solvent extraction and HS‐SPME GC‐MS in Candida tropicalis cultures. The effect of QS molecules on mono‐ and multispecies biofilms formed by Rhodotorula mucilaginosa, C. tropicalis, Candida krusei and Candida kefyr was evaluated by plate count and epifluorescence microscopy. Farnesol caused a decrease in cell number and disrupted mono‐ and multispecies yeast biofilms during adhesion (0·6 mmol l−1). 2‐phenyl ethanol 1·2 mmol l−1 stimulated biofilm density and increased cell number in both mono‐ and multispecies biofilms, while tyrosol did not show effects when tested against C. tropicalis biofilms (0·05–1·2 mmol l−1). Natamycin caused a strong decrease in cell number and disruption of biofilm structure in C. tropicalis biofilms at high concentrations (0·3–1·2 mmol l−1). The combination of farnesol 0·6 mmol l−1 and natamycin at 0·01 mmol l−1, the maximum concentration of natamycin accepted for direct addition into fruit juices, effectively reduced cell counts and disrupted the structure of C. tropicalis biofilms.
Conclusion
Farnesol 0·6 mmol l−1 significantly increased the inhibition exerted by natamycin 0·01 mmol l−1 (~5 ppm) reducing biofilm development from juice on stainless steel surfaces.
Significance and Impact of the Study
These results support the use of QS molecules as biofilm inhibitors in beverages and would certainly inspire the design of novel preservative and cleaning products for the food industry based on combinatory approaches.
Microbial strategies for biomass deconstruction involve an incredible repertoire of enzymatic, structural, and regulatory proteins. From carbohydrate active enzymes to cellulosomes, bacteria, yeast, and filamentous fungi adapt their functional machinery to grow from alternative carbon sources such as lignocellulose and survive starvation. In that context, microbes must be able to sense, bind, degrade, and utilize lignin, cellulose, and hemicelluloses. Nature has developed specialized protein modules, RNA structures, and regulatory systems operating at a genomic, transcription, and translation level. This review briefly summarizes the main regulatory pathways involved in lignocellulose microbial degradation, including carbon catabolite repression; anti-sigma factors; regulatory RNA elements such as small RNAs, antisense RNA, RNA-binding proteins, and selective RNA processing and stabilization; and transcriptional regulators and unfolded protein response. Interplay with global regulators controlling pH response and nitrogen utilization is also revised.
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