Due to the fragile cell walls of some microorganisms, high rotational speed may lead to their rupture:
Cell rupture: High shear forces can directly cause the rupture of microbial cell walls, releasing intracellular materials. This not only affects microbial survival but may also adversely impact subsequent fermentation or processing.
Metabolite leakage: After cell rupture, intracellular metabolites leak into the environment. These metabolites may be biologically active or toxic, posing potential risks to the environment and human health.
Reduced fermentation efficiency: If a large number of microbial cells rupture during fermentation, the cell concentration in the fermentation broth decreases, affecting fermentation efficiency and product yield.
For aerobic microorganisms, the mechanism of oxygen toxicity primarily involves the excessive generation of oxygen free radicals, which damage cellular components, and the imbalance of the antioxidant defense system. Under high oxygen concentrations or stress, aerobic microorganisms may experience oxidative stress, leading to cell structure and function disruption and cell death. Therefore, controlling appropriate oxygen concentration and pressure conditions is essential to ensure their normal growth and metabolic activities.
In an environment with excessively high oxygen concentration, microorganisms can suffer damage or even die. This damage mechanism may be related to the formation and attack of oxygen free radicals.
Control ventilation: During fermentation, ventilation should be adjusted according to microbial needs and tolerance to avoid excessively high or low oxygen concentrations.
Monitor oxygen concentration: Regularly monitor the oxygen concentration in the fermentation broth to ensure it remains within the optimal range.
Optimize fermentation conditions: In addition to ventilation, other conditions such as temperature, pH, and substrate concentration should be optimized to create the most suitable environment for microbial growth and product synthesis.
Strengthen equipment maintenance: Ensure fermentation equipment is in good condition to avoid abnormal ventilation caused by equipment failure.
High substrate concentration inhibits microbial metabolism, primarily due to the following reasons:
Increased osmotic pressure: Increased substrate concentration raises the osmotic pressure of the solution, thereby affecting microbial growth and reproduction. High osmotic pressure can disrupt the cell membrane, causing cell dehydration or excessive water absorption, which impacts normal cellular functions.
Metabolic pathway saturation: When substrate concentration reaches a certain level, the corresponding enzymes may become saturated, resulting in no further increase in reaction rate despite higher substrate concentration.
Metabolic overflow: Excessively high substrate concentration may trigger unnecessary metabolic pathways, leading to energy waste and by-product formation, which also affects the production of the target product.
In microbialmetabolism studies, controlling substrate concentration is crucial forregulating metabolic pathways and improving target product yield andefficiency.
Excessive product concentration significantly inhibits microbial growth and metabolism, slows fermentation, and may even cause fermentation failure. High product concentration can directly poison cells, impair enzyme activity and metabolic pathways, increase the osmotic pressure of the fermentation broth, and disrupt cellular homeostasis. Therefore, controlling the fermentation rate is critical. By adjusting culture conditions and adding inhibitors, the appropriate rate of product formation can be maintained to prevent over-accumulation. Simultaneously, improving product separation efficiency to achieve a coupled fermentation and separation process can effectively reduce product concentration, alleviate inhibition, ensure stable fermentation, and improve product yield and quality. The main solutions include coupled fermentation or perfusion culture.
Coupled fermentation technology, which integrates fermentation with product separation, is an advanced approach. By employing appropriate separation techniques such as membrane separation or extraction during fermentation, products are continuously removed from the fermentation broth, effectively reducing product concentration, relieving microbial inhibition, and improving fermentation efficiency and product yield. This process not only optimizes fermentation but also enhances product purity and recovery, making it a significant direction in modern bioprocessing.
Decreased mRNA stability: Under rapid growth conditions, mRNA stability may decline, accelerating the degradation of mRNA involved in protein synthesis.
Impaired ribosome function: While ribosome levels are not directly reduced by rapid growth, the resulting metabolic stress and resource allocation imbalance can indirectly impair ribosome function. For example, ribosomes may not receive sufficient energy or amino acids to support efficient protein synthesis.
Abnormal protein folding and modification: Due to the lack of Golgi apparatus and endoplasmic reticulum, rapidly growing cells may not provide an adequate environment for protein folding and modification. This can result in misfolded proteins or the absence of necessary modifications such as glycosylation and phosphorylation, affecting protein function and stability.
For prokaryotic microorganisms, controlling growth rate by adjusting medium composition, feeding strategy, and temperature helps maintain intracellular metabolic balance and gene expression stability, thereby improving protein synthesis efficiency and quality.
In microbial processes, controlled fermentation is essential for maintaining balance across all stages. By fine-tuning the fermentation rate, the distribution of biomass, nutrients, and energy can be optimized. Through segmented process design, the microbial growth cycle is comprehensively considered, ensuring optimal growth conditions and avoiding resource waste or product inhibition caused by excessively fast or slow rates. Rate-controlled fermentation is a key strategy in modern bioprocessing to maximize resource utilization and improve product quality and yield.