Exploration of sulfur metabolism in the yeast Kluyveromyces lactis

Abstract

Hemiascomycetes are separated by considerable evolutionary distances and, as a consequence, the mechanisms involved in sulfur metabolism in the extensively studied yeast, Saccharomyces cerevisiae, could be different from those of other species of the phylum. This is the first time that a global view of sulfur metabolism is reported in the biotechnological yeast Kluyveromyces lactis. We used combined approaches based on transcriptome analysis, metabolome profiling, and analysis of volatile sulfur compounds (VSCs). A comparison between high and low sulfur source supplies, i.e., sulfate, methionine, or cystine, was carried out in order to identify key steps in the biosynthetic and catabolic pathways of the sulfur metabolism. We found that sulfur metabolism of K. lactis is mainly modulated by methionine. Furthermore, since sulfur assimilation is highly regulated, genes coding for numerous transporters, key enzymes involved in sulfate assimilation and the interconversion of cysteine to methionine pathways are repressed under conditions of high sulfur supply. Consequently, as highlighted by metabolomic results, intracellular pools of homocysteine and cysteine are maintained at very low concentrations, while the cystathionine pool is highly expandable. Moreover, our results suggest a new catabolic pathway for methionine to VSCs in this yeast: methionine is transaminated by the ARO8 gene product into 4-methylthio-oxobutyric acid (KMBA), which could be exported outside of the cell by the transporter encoded by PDR12 and demethiolated by a spontaneous reaction into methanethiol and its derivatives.

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

“…4). Our previous results confirmed the absence of hypotaurine and taurine pools in Kluyveromyces lactis (17). The hypotaurine and taurine pools, which are increased under high-methionine conditions, could serve as a sulfur reservoir.…”

“…K. lactis, a hemiascomycetous yeast that is more closely related to S. cerevisiae, also possesses these two pathways (16). Meanwhile, we observed an absence of regulation of the OAS pathway and a regulation of the transsulfuration pathway in K. lactis (17) that was identical to that observed in S. cerevisiae (25). This suggests that cysteine biosynthesis could be regulated differently in Y. lipolytica.…”

“…The specific growth rate was appreciably the same under all of the conditions studied (0.28 Ϯ 0.01 h Ϫ1 [value obtained from three repetitions for each condition]). These precautions ensured highly reproducible growth conditions (17).…”

“…The Yarrowia lipolytica strain 1E07 (isolated from a Livarot cheese) was chosen for its interesting biotechnological properties during cheese ripening. This strain was grown in a defined sulfur-free medium (SM) (17) supplemented with sulfur sources as follows: 10 mM L-methionine, 1 mM L-cystine, or 10 mM (NH 4 ) 2 SO 4 for high concentrations and 10 M L-methionine, 1 M L-cystine, or 10 M (NH 4 ) 2 SO 4 for low concentrations. Cysteine, which is very reactive, can spontaneously dimerize and form cystine.…”

Novel Cysteine-Centered Sulfur Metabolic Pathway in the Thermotolerant Methylotrophic Yeast Hansenula polymorpha

“…the forward transsulfuration reaction, which is mediated by HpSTR2 and HpSTR3 proteins. It is quite intriguing that sulfur metabolism of H. polymorpha is centered on cysteine rather than methionine, in contrast to other hemiascomycetes such as S. cerevisiae and Kluyveromyces lactis [30].…”