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Discovering inhibitory effects in fed-batch cultures: Why aren't your microbes growing
With the advancement of biotechnology, fed batch culture technology has gradually become a key operation in major production processes. This technology can not only effectively improve the growth of microorganisms and the production of metabolites, but also help scientists solve many challenges faced by traditional culture methods. However, faced with the inhibitory effects that occur during the cultivation of various microorganisms, researchers are still puzzled as to why some microorganisms do not grow under specific conditions.
Fed-batch culture is an operating technology that continuously supplies one or more nutrients (substrates) during the culture process and retains the product in the bioreactor until the end of the run.
The advantage of fed-batch culture technology is that it can flexibly control the concentration of substrate in the culture medium, thereby affecting the growth and metabolism of microorganisms. In some cases, this technique is superior to conventional batch cultures, particularly when nutrient concentrations affect the yield or efficiency of production of the desired metabolite. However, this seemingly ideal technology often encounters the challenge of inhibitory effects in practical applications.
Types of inhibitory effects
During feeding batch culture, there are several typical inhibitory effects:
Substrate InhibitionCertain nutrients, such as methanol, ethanol, acetic acid, and aromatic compounds, can inhibit microbial growth even at relatively low concentrations. By appropriately adding such substrates, the lag time can be shortened and the inhibition of cell growth can be significantly reduced.
High cell density
In batch cultures, achieving very high cell densities often requires the addition of high initial concentrations of nutrients to the culture medium. However, at such high concentrations, nutrients will become inhibitory. This requires adjustment through feeding techniques.
In baker's yeast production, even in the presence of adequate dissolved oxygen, excess sugar in the culture will produce ethanol, resulting in low cell yields.
Crabbitt Effect
High sugar concentrations lead to ethanol formation, which not only affects growth but also produces harmful by-products, so a fed-batch process is generally used in baker's yeast production to reduce this effect.
Metabolite Inhibition
When microorganisms are cultured aerobically at high sugar concentrations, organic acids such as lactic acid and acetic acid are produced as by-products, which inhibit cell growth and impair their metabolic activities.
Gas Suppression
In some culture processes, such as the production of penicillin, the oxygen demand of the microorganisms must be kept within certain limits. Once too much oxygen is provided, the formation of specific metabolites will be inhibited, affecting the yield of the final product.
Microbial Growth Control Strategies
Also, due to the controllable nature of fed-batch cultures, many strategies have been used to control microbial growth. For example, in high-density culture, the growth rate is maintained by continuously supplying the limiting substrate; in the case of stable feeding, the feeding rate is adjusted according to the growth situation to avoid the emission of side metabolites; in directing enzyme synthesis, the growth rate is controlled by limiting the growth rate. Substrate supply alleviates the inhibitory effect and promotes the synthesis of required substances.
ConclusionMaintaining the concentration of a specific compound at a minimum while maintaining continuous gene expression is one of the important applications of fed-batch cultures.
With the continuous advancement of science and technology, fed batch culture technology will receive more and more attention. Researchers urgently need to conduct in-depth studies on the inhibitory effects faced by various microorganisms during cultivation and explore how to overcome these challenges through different cultivation strategies. When faced with a variety of potential influencing factors, how can we readjust our microbial cultivation strategies to cope with these adverse growth environments?
