Controlled transient changes reveal differences in metabolite production in two Candida yeasts

Area of Science:

• Biochemistry
• Microbiology
• Metabolic Engineering

Background:

• Candida yeasts are crucial in industrial bioprocesses.
• Understanding xylose metabolism is key for optimizing bio-production.
• Oxygen availability significantly influences yeast metabolic pathways.

Purpose of the Study:

• To investigate the physiological responses of Candida tropicalis and Candida guilliermondii during xylose growth.
• To elucidate the xylose-degrading pathways and cofactor regeneration mechanisms in these yeasts.
• To compare the effects of varying oxygen levels and formate co-substrate addition on xylose metabolism.

Main Methods:

• Cultivation of Candida tropicalis and Candida guilliermondii under controlled oxygen transfer and dilution rates.
• Analysis of metabolic products (acetate, ethanol, glycerol) and cofactor regeneration (NADPH, NAD).
• Assessment of xylose uptake rates and the impact of formate feeding on metabolic flux.

Main Results:

• Candida guilliermondii produced acetate (regenerating NADPH) and glycerol, while Candida tropicalis produced ethanol (regenerating NAD) and glycerol.
• D-xylose reductase in C. guilliermondii is NADPH-dependent, whereas C. tropicalis utilizes both NADH and NADPH.
• Formate feeding in C. tropicalis led to glycerol, ethanol, and xylitol accumulation, increasing specific xylose consumption by 28%.

Conclusions:

• Yeast strains exhibit distinct strategies for xylose metabolism and cofactor regeneration under oxygen limitation.
• Metabolic engineering approaches, such as formate feeding, can enhance xylose utilization efficiency in Candida species.
• The differential cofactor dependency of xylose reductase influences metabolite production and overall metabolic flux.