Through the combined effects of constant temperature and oscillation, a constant-temperature shaker influences the shape, size, and edge regularity of microbial colonies. Appropriate shaker conditions can promote a more uniform distribution of colonies across the culture dish, thereby preventing colony overlap and cross-contamination.
I. The Impact of Shaker Amplitude on Samples
1. Both the amplitude and rotational speed of the shaker affect the Oxygen Transfer Rate (OTR) within the culture medium; a higher OTR value indicates higher oxygen transfer efficiency. The better the mixing effect, the higher the oxygen transfer rate (OTR). Generally speaking, a larger amplitude and a faster rotational speed result in higher OTR and greater dissolved oxygen efficiency. The specific levels of rotational speed and amplitude have a particularly pronounced impact on microorganisms with high oxygen consumption requirements, as well as on strains that are highly sensitive to dissolved oxygen levels. For instance, in experiments involving processes with high oxygen demand—such as citric acid fermentation—a rotational speed that is too low can lead to a significant reduction in the number of viable cells.
2. In cell culture applications conducted at very low rotational speeds (e.g., 100 rpm), variations in amplitude have almost no discernible effect on oxygen transfer. However, excessively high rotational speeds can generate excessive shear forces; certain microorganisms that are sensitive to shear stress may perish as a result of such high-speed agitation.
II. The Impact of Shaker Temperature on Samples
1. Temperature exerts a highly significant influence on both the number of spores produced during fermentation and the total count of viable cells. Generally, the optimal survival temperature for microorganisms falls within the range of 20°C to 35°C; temperatures that are either too high or too low can lead to microbial inactivation or even death. From the perspective of enzyme reaction kinetics, an increase in temperature accelerates reaction rates, boosts metabolic activity, and hastens the production of target products. However, as temperature rises, the rate of enzyme inactivation also increases, causing microbial cells to age prematurely and ultimately compromising product yield.
2. Furthermore, the optimal temperature required for the growth of a specific microorganism may differ from the optimal temperature required for the accumulation of its metabolic products. For instance, the optimal temperature for the growth of penicillin-producing microorganisms is 30°C, whereas the optimal temperature for actual penicillin production is 25°C. Similarly, *Aspergillus niger* grows optimally at 37°C, yet the production of glucoamylase and citric acid occurs most efficiently within the range of 32°C to 34°C. Consequently, it is necessary to adjust the temperature based on the specific product being manufactured and to set distinct temperature parameters for the various stages of the production process.
3. Temperature also influences the composition of enzyme systems and the specific characteristics of individual enzymes. For example, enzymes produced during cultivation at 55°C retain 88% to 99% of their residual activity after being held at 90°C for 60 minutes; in contrast, enzymes produced during cultivation at 35°C, when subjected to the same treatment conditions, retain only 6% to 10% of their residual activity.
4. Varying temperatures also exert distinct effects on the metabolic products generated by microorganisms. For instance, when utilizing *Streptomyces aureofaciens* strain NRRL B-1287 for tetracycline fermentation, maintaining the fermentation temperature below 30°C leads to an increased synthesis of chlortetracycline. Conversely, raising the fermentation temperature favors the synthesis of tetracycline. At 35°C, *S. aureofaciens* produces exclusively tetracycline, while the synthesis of chlortetracycline virtually ceases.
5. Furthermore, temperature affects the physical properties of the fermentation broth—such as its viscosity, as well as the solubility and mass transfer rates of substrates and oxygen within the liquid medium, and the decomposition and uptake rates of specific substrates. By influencing these aforementioned conditions, fermentation temperature ultimately impacts the kinetic characteristics of the fermentation process and the biosynthesis of the target product.