Gene Expression and Biochemical Analysis of Cheese-Ripening Yeasts: Focus on Catabolism of
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            -Methionine, Lactate, and Lactose

The consumption of lactate and amino acids is very important for microbial development and/or aroma production during cheese ripening. A strain of Yarrowia lipolytica isolated from cheese was grown in a liquid medium containing lactate in the presence of a low (0.1؋) or high (2؋) concentration of amino acids. Our results show that there was a dramatic increase in the growth of Y. lipolytica in the medium containing a high amino acid concentration, but there was limited lactate consumption. Conversely, lactate was efficiently consumed in the medium containing a low concentration of amino acids after amino acid depletion was complete. These data suggest that the amino acids are used by Y. lipolytica as a main energy source, whereas lactate is consumed following amino acid depletion. Amino acid degradation was accompanied by ammonia production corresponding to a dramatic increase in the pH. The effect of adding amino acids to a Y. lipolytica culture grown on lactate was also investigated. Real-time quantitative PCR analyses were performed with specific primers for five genes involved in amino acid transport and catabolism, including an amino acid transporter gene (GAP1) and four aminotransferase genes (ARO8, ARO9, BAT1, and BAT2). The expression of three genes involved in lactate transport and catabolism was also studied. These genes included a lactate transporter gene (JEN1) and two lactate dehydrogenase genes (CYB2-1 and CYB2-2). Our data showed that GAP1, BAT2, BAT1, and ARO8 were maximally expressed after 15 to 30 min following addition of amino acids (BAT2 was the most highly expressed gene), while the maximum expression of JEN1, CYB2-1, and CYB2-2 was delayed (>60 min).

Section: Discussionmentioning

confidence: 95%

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confidence: 87%

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confidence: 99%

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Lactate and Amino Acid Catabolism in the Cheese-Ripening Yeast Yarrowia lipolytica

Mansour

Beckerich

Bonnarme

2008

“…This is at least partly due to the technical difficulties associated with isolating representative cell samples from the solid fermentation matrix. Some studies have attempted to gain insight into bread fermentation by mimicking the process in liquid (15)(16)(17). Whereas such studies definitely contributed to our knowledge, they change the single most important parameter of SSFs (the solid state) and are therefore not an optimal model for the industrial SSF process.…”

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confidence: 99%

Dynamics of the Saccharomyces cerevisiae Transcriptome during Bread Dough Fermentation

Aslankoohi

Zhu

Rezaei

et al. 2013

The behavior of yeast cells during industrial processes such as the production of beer, wine, and bioethanol has been extensively studied. In contrast, our knowledge about yeast physiology during solid-state processes, such as bread dough, cheese, or cocoa fermentation, remains limited. We investigated changes in the transcriptomes of three genetically distinct Saccharomyces cerevisiae strains during bread dough fermentation. Our results show that regardless of the genetic background, all three strains exhibit similar changes in expression patterns. At the onset of fermentation, expression of glucose-regulated genes changes dramatically, and the osmotic stress response is activated. The middle fermentation phase is characterized by the induction of genes involved in amino acid metabolism. Finally, at the latest time point, cells suffer from nutrient depletion and activate pathways associated with starvation and stress responses. Further analysis shows that genes regulated by the high-osmolarity glycerol (HOG) pathway, the major pathway involved in the response to osmotic stress and glycerol homeostasis, are among the most differentially expressed genes at the onset of fermentation. More importantly, deletion of HOG1 and other genes of this pathway significantly reduces the fermentation capacity. Together, our results demonstrate that cells embedded in a solid matrix such as bread dough suffer severe osmotic stress and that a proper induction of the HOG pathway is critical for optimal fermentation.

“…The strong proteolytic, lipolytic, and esterasic (split of esters into acid and alcohol) activities (3)(4)(5) of Y. lipolytica are particularly interesting for cheese aromatization, because this yeast produces large quantities of aroma precursors from caseins and milk fat hydrolysis, leading to various aromatic compounds. As a consequence, it has already been reported that Y. lipolytica produces a wider variety and quantity of volatile sulfur compounds (VSCs) than other commonly found cheese-ripening yeasts, such as Debaryomyces hansenii and Kluyveromyces lactis (6,7). Its recurrent presence in soft cheeses due to inoculation from the environment (e.g., brine, ripening shelves, and personnel) is therefore indicative of its noteworthy adaptation to the cheese biotope and its positive effect on the aromatic quality of various soft cheeses (8).…”

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confidence: 99%

New Insights into Sulfur Metabolism in Yeasts as Revealed by Studies of Yarrowia lipolytica

Hébert

Forquin-Gomez

Roux

et al. 2013

Self Cite

Yarrowia lipolytica, located at the frontier of hemiascomycetous yeasts and fungi, is an excellent candidate for studies of metabolism evolution. This yeast, widely recognized for its technological applications, in particular produces volatile sulfur compounds (VSCs) that fully contribute to the flavor of smear cheese. We report here a relevant global vision of sulfur metabolism in Y. lipolytica based on a comparison between high-and low-sulfur source supplies (sulfate, methionine, or cystine) by combined approaches (transcriptomics, metabolite profiling, and VSC analysis). The strongest repression of the sulfate assimilation pathway was observed in the case of high methionine supply, together with a large accumulation of sulfur intermediates. A high sulfate supply seems to provoke considerable cellular stress via sulfite production, resulting in a decrease of the availability of the glutathione pathway's sulfur intermediates. The most limited effect was observed for the cystine supply, suggesting that the intracellular cysteine level is more controlled than that of methionine and sulfate. Using a combination of metabolomic profiling and genetic experiments, we revealed taurine and hypotaurine metabolism in yeast for the first time. On the basis of a phylogenetic study, we then demonstrated that this pathway was lost by some of the hemiascomycetous yeasts during evolution.