Minimal nutritional requirements for immobilized yeast

Area of Science:

• Biotechnology
• Biochemical Engineering
• Microbial Physiology

Background:

• Immobilized cell reactors (ICRs) offer benefits like reduced cell growth and clogging.
• Minimizing nutrient levels can decrease operational costs and waste disposal.

Purpose of the Study:

• To investigate the impact of reduced nutritional levels, particularly nitrogen, on immobilized yeast (K. fragilis) productivity.
• To determine the minimum nutrient requirements for sustained productivity in an ICR.
• To explore the relationship between cell growth and productivity under nutrient limitation.

Main Methods:

• Utilized a trickle flow, plug flow reactor with yeast immobilized on a packing matrix.
• Monitored gas evolution rates and effluent cell density to assess productivity and growth.
• Introduced step changes in nutrient composition, including reduced nitrogen sources (ammonium sulfate, yeast extract, peptone).

Main Results:

• Stable productivity was maintained for 80 hours with only essential salts, demonstrating decoupling of growth and productivity.
• Productivity dropped by 35-65% and growth rates by 75-95% upon nutrient elimination.
• A minimum yeast extract concentration of 0.375 g/L (with or without ammonium sulfate) sustained increased productivity, a 94% reduction from standard YEP medium.

Conclusions:

• Nutritional deficiencies largely decouple growth and productivity in immobilized yeast.
• Productivity in ICRs is both growth- and non-growth-associated.
• Significant cost savings are achievable by reducing nutrient levels in feed streams for ICRs.