The Complete Pathway for Thiosulfate Utilization in Saccharomyces cerevisiae

Area of Science:

• Microbiology
• Biochemistry
• Industrial Biotechnology

Background:

• Saccharomyces cerevisiae utilizes thiosulfate as a sulfur source, leading to increased ethanol production compared to sulfate.
• Understanding the assimilation pathway of thiosulfate is crucial for optimizing industrial fermentation processes.

Purpose of the Study:

• To elucidate the complete molecular mechanism by which Saccharomyces cerevisiae assimilates thiosulfate.
• To identify the key enzymes and transporters involved in thiosulfate uptake and metabolism.
• To explore the implications of this pathway for other organisms and industrial applications.

Main Methods:

• Investigated thiosulfate uptake using specific yeast strains and permease mutants (Sul1, Sul2).
• Analyzed thiosulfate conversion using rhodanese enzymes (Rdl1, Rdl2) and subsequent metabolic products.
• Determined the role of hydrogen sulfide and cysteine synthase in the assimilation pathway.

Main Results:

• Thiosulfate is absorbed by sulfate permeases Sul1 and Sul2.
• Rhodanese enzymes convert thiosulfate into persulfide and sulfite, which are further reduced to hydrogen sulfide (H2S).
• Hydrogen sulfide is incorporated into O-acetyl-l-homoserine by cysteine synthase, forming l-homocysteine, a precursor for cysteine and methionine.

Conclusions:

• The study fully characterizes thiosulfate assimilation in Saccharomyces cerevisiae, highlighting significant overlap with sulfate assimilation pathways.
• Rhodanese is identified as the key enzyme for thiosulfate utilization, suggesting broad applicability across Bacteria, Archaea, and Eukarya.
• Thiosulfate assimilation is energetically favorable compared to sulfate, positioning it as a potential sulfur source for optimized industrial fermentation.