Effect of aeration on growth of bacteria

 Aim

To study the effect of aeration on growth of bacteria

Principle

Microorganisms are classified into categories such as aerobic, facultative anaerobic, and anaerobic bacteria depending on their metabolic strategies influenced by the availability of oxygen. Aerobic bacteria or obligate aerobes, require oxygen for their growth and survival as they utilize oxygen as the final electron acceptor in their electron transport chain that yields a large amount of ATP. In contrast, anaerobic bacteria or obligate anaerobes do not require oxygen for growth and they rely on anaerobic respiration or fermentation, metabolic pathways that generate energy without oxygen by using alternative electron acceptors such as nitrate, sulfate, carbon dioxide or by relying solely on substrate-level phosphorylation. Facultative anaerobic bacteria possess metabolic flexibility to grow both in the presence or absence of oxygen.

Aeration is a critical factor in microbial growth, particularly for aerobic and facultative anaerobic microorganisms, as it directly impacts the availability of dissolved oxygen (DO) in the culture medium. Oxygen is essential for respiration and other metabolic processes in aerobic organisms, serving as the final electron acceptor in the electron transport chain.  For facultative anaerobic bacteria, even though they can survive and grow both with or without oxygen, aeration plays a significant role in their growth.  When oxygen is available, they preferentially switch to aerobic respiration since it is metabolically much more efficient. As a result, in well-aerated conditions, aerobes and facultative anaerobes will exhibit faster growth rates, reach higher cell densities, and utilize their carbon sources more completely than in unaerated conditions.

Materials required

1. Culture of E coli and Bacillus spp.

2. Sterile Nutrient broth flasks, Shaker incubator, other routine microbiological facilities

 

Procedure

1. Nutrient broth flasks were labelled with the organism to be inoculated, E coli and Bacillus spp.

2. One set of inoculated flasks was placed on an orbital shaker incubator set to 37°C with a shaking speed of 150-250 rpm. A second set of inoculated flasks was placed in a static incubator at 37°C. Both were incubated for 24-48 hours.

3. The flasks were observed, after incubation and the optical density at 600 nm was recorded

 

Observation and result

The bacterial species were found to have different growth patterns under aerated and static conditions.  For both organisms, maximum growth was observed under aerated conditions.

 

  

Effect of aeration on bacterial growth (left hand side)

Microorganism	OD at 600 nm
	Under static conditions	At shaker incubator 150 rpm
E coli	0.24	0.90
Bacillus sp	0.11	0.58