What is the Difference Between Axenic and Mixed Culture

The main difference between axenic and mixed culture is that a single species, variety, or strain occurs in axenic culture while two or more organisms occur in mixed culture. 

Axenic and mixed cultures are two cultures where bacteria or unicellular eukaryotes grow.   

Key Areas Covered

1. What is Axenic Culture
– Definition, Preparation, Importance
2. What is Mixed Culture
– Definition, Facts, Advantages
3. Similarities Between Axenic and Mixed Culture
– Outline of Common Features
4. Difference Between Axenic and Mixed Culture
– Comparison of Key Differences

Key Terms 

Axenic Culture, Mixed Culture

What is Axenic Culture

The axenic culture is a state of culture in which only one species, variety, or strain of microorganisms live. Therefore, this type of culture is entirely free of other contaminating organisms that grow in the culture. Also, bacteria and other unicellular microorganisms can grow in axenic culture. Subculturing from an existing mixed culture is the preparation method of an axenic culture. It involves diluting the mixed culture to the point where the subculture only contains a single type of microorganism. An axenic culture selects the cultures that solely grow the desired organism.

Figure 1: Ascomycetes

Furthermore, the genomes of the microorganisms that grow in the axenic culture contain a relatively narrow gene pool. In the case of asexual species, the culture comprises identical organisms. Only the mutations and horizontal gene transfer introduce the degree of variability. Therefore, the characteristics of the organisms in an axenic culture are more uniform and reproducible. However, axenic cultures are essential for genome sequencing and molecular studies. Also, they are important in biomass and metabolite production. Additionally, they are necessary for the discovery of bioactive products. 

What is Mixed Culture

A mixed culture is a state of culture in which two or more microorganisms grow simultaneously. It may consist of a known species mixing with unknown species. Also, it may contain one microbial group, such as all bacteria, or a mixture of microorganisms, such as fungi, bacteria, and yeast. In contrast to the axenic culture, a mixed culture may have several advantages. Mixed cultures may have a high product yield. For example, yogurt is a product of milk fermentation by two microorganisms: Streptococcus thermophilus and Lactobacillus bulgaricus. Also, the growth rate of microorganisms is higher in mixed cultures. In mixed culture, microorganisms produce growth factors and other essential compounds for growth that are beneficial for a second organism.

Figure 2: Agar-Mixed Culture of Salmonella sp and Escherichia coli

Moreover, mixed cultures bring multistep transformations that are impossible in axenic cultures. In miso and shoyu fermentation, Aspergillus oryzae strains produce koji that produces amylases and proteases to degrade the starch in rice and proteins in soybeans, respectively. Then, lactic acid bacteria and yeast produce flavor compounds and alcohol. Additionally, microorganisms in mixed cultures are remarkably stable in the association. For example, in ragi, the mixture of fungi, bacteria, and yeast remains together even after years of subculture. 

Similarities Between Axenic and Mixed Culture

• Axenic and mixed cultures are two types of cultures used to grow microorganisms.
• Bacteria and unicellular eukaryotes are grown in these cultures.
• These cultures are essential to study symbiotic and parasitic organisms. 

Difference Between Axenic and Mixed Culture

Definition

Axenic culture contains only one species, variety, or strain of organisms. In contrast, mixed culture refers to one with more than one type of organism growing in a sterile medium, such as agar.

Structure

Axenic culture contains only one type of microorganism, while mixed culture includes more than one type of microorganism.  

Applications

Axenic culture is essential for genome sequencing and molecular studies, while mixed culture is vital to determine interactions between microorganisms. 

Conclusion

In brief, axenic and mixed cultures are two types of cultures that allow the growth of microorganisms. Axenic culture contains only one kind of microorganism growing in the culture. It is essential for molecular studies and genome sequencing. In comparison, mixed culture includes two or more types of microorganisms growing in the culture. However, it is necessary for the determination of interactions between microorganisms. Therefore, the main difference between axenic and mixed culture is the number of microorganisms that grow.  

References:

1. Wikimedia Foundation. (2021, October 23). Axenic. Wikipedia. https://en.wikipedia.org/wiki/Axenic
2. National Research Council (US) Panel on the Applications of Biotechnology to Traditional Fermented Foods. Applications of Biotechnology to Fermented Foods: Report of an Ad Hoc Panel of the Board on Science and Technology for International Development. Washington (DC): National Academies Press (US); 1992. 6, Mixed-Culture Fermentations.

Image Courtesy:

1. “Ascomycetes” By Dr. David Midgley – Own work (CC-BY SA 2.5) via Commons Wikimedia
2. “XLD Agar-mixed culture of Salmonella sp and Escherichia coli (6500349623)” By Michael R Francisco – Own Work (CC-BY 2.0) via Commons Wikimedia