Amino Acid Depletion Reveals Strain- and Nitrogen Source-Dependent Physiological Responses in Brettanomyces...

Fungal nitrogen metabolism is a central determinant of yeast growth, fermentative performance, and secondary metabolism in fungi associated with fermented environments. For Saccharomyces cerevisiae, the assimilation of nitrogen sources found in grape must, including ammonium, free amino acids, and peptides, has been widely characterized, establishing a consumption hierarchy in which proline is considered a non-preferential nitrogenous source. However, the regulation and hierarchy of nitrogen-source utilization in non-conventional fungi remain poorly characterized, particularly in yeasts adapted to anthropized fermentative niches. In this context, Brettanomyces bruxellensis represents a useful fungal model to study the different nitrogen sources that are used, strain-dependent physiology, and survival under nutrient-limited fermentative conditions. We hypothesized that apparent depletion of amino acid and the expression of selected amino acid permease genes are strain-dependent traits linked to the survival of B. bruxellensis. In this study, we evaluated the strain-dependent physiology and amino acid depletion patterns of two B. bruxellensis strains from wine (LAMAP2480 and LAMAP1359). In both cases, the highest apparent depletion values under the 20 amino acid condition were observed for arginine, glutamine, tryptophan and proline, indicating that these compounds contributed substantially to the organic nitrogen pool under the assayed conditions. Only LAMAP2480 isolate was able to grow in the condition without added amino acids, indicating strain and nitrogen source dependence under limited organic nitrogen availability. Transcriptional analysis of GAP1, GNP1, and TAT1 permeases showed expression patterns dependent on both the strain and the available nitrogen source. This is the first study to combine the evaluation of physiological performance, amino acid consumption, apparent nitrogen depletion derived from amino acids normalized to OD₆₀₀ (OD-AA-N depletion), and the transcriptional responses of selected amino acid permease genes. This knowledge may contribute to understanding the survival of B. bruxellensis in fermentation environments with limited nutritional resources.