What are the types of fed-batch culture?

The four types of fed-batch culture include: Fixed-volume fed-batch culture, repeated or cyclic fed-batch culture, single-fed batch culture process and variable-volume fed-batch culture. 

1. In fixed-volume fed-batch culture, the limiting substrate is continuously added to the reactor in a highly concentrated form, ensuring that the volume of the culture remains relatively constant. This approach is often used for organisms that thrive in specific environmental conditions, like hyperthermophilic Archaebacteria. 
2. In single fed batch-process, a feeding solution is added during the fermentation, but spent broth is not removed. 
3. The repeated or cyclic fed-batch culture involves periodically removing spent broth from the fermenter and replacing it with fresh nutrient medium. This cycle helps maintain optimal conditions for growth by replenishing nutrients and removing inhibitory by-products. It's commonly used for optimizing conditions in processes like penicillin G biosynthesis. 
4. In variable-volume fed-batch culture, the volume of the culture changes over time as substrate feed is added. This flexibility allows for adjustments based on procedure requirements. The feeding strategy can vary, such as adding only the limiting substrate or gradually adding concentrated substrate to prevent excessive dilution of the culture.