Aerobic and Anaerobic Culture Methods

Microbial culture is used to multiply and study microorganisms by providing them with a controlled nutrient media and under ideal laboratory conditions. The major constituents of a culture media can be listed as follows:

• Energy source

• Carbon source
• Salts
• Nitrogen source
• pH
• Growth factors etc.

The aerobic and anaerobic culture methods are distinguished based on growth in the presence of oxygen. They are:

• Aerobes- These are organisms that can grow up to some extent in the presence of oxygen.
• Obligate Aerobes- Organisms that cannot grow in the absence of oxygen.
• Anaerobes- These are organisms that generally grow well in low oxygen content environments.
• Obligate anaerobes- Organisms that die in the presence of oxygen and grow in extreme oxygen-less environments.

Aerobic Culture Methods:

The growth media is selected based on the type of microbe to be cultured. A rich and complete media is generally used for growing a pure (containing a particular strain of the microbe) microbial line in bulk. At the same time, minimal media is essential for regulating a specific pathway in the microbe. We should also consider that these cultures need to be grown in sterile conditions. The growth phase of bacteria can be divided into four stages:

• Lag Phase-The bacteria adjust themselves to their new surroundings.
• Log Phase- This is the growth phase of the culture. The bacteria divide rapidly to multiply at an exponential rate.
• Stationary Phase-Due to nutrient utilization and waste material build-up, the growth rate slows down to become equal to the death phase.
• Death Phase- Due to unfavourable conditions, there is a steady decline in the number of cells, and the amount of death surpasses the amount of bacterial growth.

Anaerobic Culture Methods:

Anaerobic bacteria have to be cultivated in the absence of oxygen. Thus proper care has to be taken to ensure it. The culture media generally consists of brain-heart infusion, vitamin K, and amino acids. The use of culture media depends on the type of specimen of bacteria. The cultures are grown in an oxygen-free environment at 95 degrees F for 48 hours. Entirely sealed cabinets of plastic are used to produce the microbes. The interior composition of gases generally consists of 10% hydrogen, 10% carbon dioxide and 80% nitrogen.

Applications of Microbial Culture:

Once the microbe is grown using aerobic and anaerobic culture methods reaches a phase of stable growth, they can be used for a variety of purposes such as:

• Diagnosis: Culturing microbes and testing them subsequently to identify the microbe can help us identify the cause of a disease. This is of prime medical importance. The samples for such study can be extracted from wounds, blood, urine and other body fluids. 
• Drug Discovery: The vast array of antibiotics available in the market would not have been possible without the culturing and further testing of bacteria in Petri dishes. The vast library of possible antibiotic targets is tested after culturing bacteria to select potential drug candidates. This is a long and cost-intensive process.
• Studying microbial colonies: It has been observed that microbes can behave differently in colonies instead of when they are present individually. Such studies have proven that there is a constant cross-talk between neighbouring microbes. They communicate with the help of quorum sensing, sporulation, contact signalling etc. 
• Creating models: Recombinant DNA Technology has allowed us to insert certain genes and study their interactions in microbes. This allows us to understand the functional aspect of the gene using knockout studies. So the creation of such models has helped us to form a holistic understanding of the genome.

Anaerobic Bacteria Test Methods:

Anaerobic and aerobic microbes can be separated by first culturing them using aerobic and anaerobic culture methods in a test tube of thioglycollate broth. Now, based on the position of the growth of the microbe, we can classify them:

• Obligate aerobes grow at the top.
• Obligate anaerobes gather at the bottom of the tube.
• Facultative anaerobes are present everywhere but are present at a higher concentration at the top
• Microaerophiles gather at the upper part of the test tube but not at the top
• Aerotolerant organisms are distributed evenly throughout the test tube.

Thus, by following this test, we can easily distinguish our anaerobic microbe.

Conclusion:

Aerobic and anaerobic culture methods provide a powerful tool that helps us selectively grow microbes of our choice. The growth conditions are manipulated to provide the most optimal situation for growth. This ensures that we get a pure and dense culture of cells. These are further processed to generate secondary cultures for further use. It is essential to classify and separate the aerobes from the anaerobes as the diseases caused by them can vary, which helps us in early diagnosis and proper treatment. Finally, we looked at test methods to differentiate between the groups of microbes based on their demand for oxygen.