Facultative Anaerobes

What is Facultative Anaerobe?

Anaerobes are microorganisms that can survive in the lack of free oxygen; obligatory, also known as stringent microbes are anaerobes that can only survive in the anaerobic environment. Some species, known as facultative anaerobes, can support the growth both in the presence or absence of free oxygen. Microaerophiles, on the other hand, are organisms that thrive in low oxygen environments. Let us see the facultative anaerobe definition that will help us in understanding the concept of the facultative anaerobe and facultative anaerobic process. 

Facultative anaerobe definition in biology, a microbe that can produce energy via aerobic respiration but then shift to anaerobic respiration based on the quantity of oxygen and fermentable content present in the environment. The facultative anaerobes examples include E. Coli and yeast. The article focuses on the discussion of the facultative anaerobe definition, facultative anaerobes examples. Ecological Importance of Facultative Anaerobes and a comparative study between the obligate anaerobes vs facultative anaerobe is also mentioned in the article.


What is Aerobic and Anaerobic Respiration?

Let us briefly understand what is aerobic and anaerobic respiration to develop the understanding of facultative anaerobic bacteria. Aerobic respiration is the process of breaking down glucose in the presence of oxygen in order to generate energy in the form of compounds like ATP. The cascade of reactions is catalyzed by enzymes can be defined as aerobic respiration. 

The method entails the movement of electrons between compounds that serve as a source of the substrate, such as glucose, to oxygen, which serves as the terminal electron acceptor. Aerobic respiration is the most important mechanism for generating energy. Finally, this strategy offers ATP and metabolic intermediates for a variety of additional cell pathways, including carbohydrate, lipids, and protein synthesis.

The chemical equation mentioned below will help in better understanding the concept.

C6H12O6 + 6O2 → Energy + 6H2O + 6CO2                          

Anaerobic respiration is differentiated from that of aerobic respiration with respect to the requirement of oxygen while converting the given substrate such as glucose into energy. 

The breakdown of glucose in the absence of oxygen to produce energy is called anaerobic respiration. Some bacteria have evolved a system that uses oxygen-containing salts as an electron acceptor rather than free oxygen. The energy produced by anaerobic respiration is useful when there is a high demand for energy. However, when compared to aerobic respiration, it is produced in much smaller amounts.

The chemical reaction mentioned below will help in understanding the concept of anaerobic respiration. 

C6H12O6 + 6O2 → 2C3H6O3 + Energy


Facultative Anaerobic Bacteria

The facultative anaerobic bacteria are those bacteria that can survive and grow in both aerobic and anaerobic conditions. One of the common facultative anaerobes examples in the bacterial category is E.coli. Enterobacteriaceae, Vibrionaceae, and Pasteurellaceae are the three major families of facultative anaerobic bacteria.

Since the facultative anaerobic bacteria can perform respiration in both conditions there are three cellular pathways for energy production of these microbes, they are aerobic respiration, anaerobic respiration, and fermentation. As we have already discussed the anaerobic and aerobic respiration, let us understand fermentation. 

Fermentation is the process by which large and complex organic acids and sugar molecules are broken down into a simpler form that can be utilized to generate chemical energy. Chemical energy, usually in the form of ATP, is crucial because it powers a variety of biological functions. Fermentation is seen in obligate anaerobes and facultative anaerobe because it does not consume oxygen. Another key aspect to remember is that the electrons are not passed through the electron transport chain system to the ultimate electron acceptor. An organic compound, such as pyruvate in lactic acid fermentation or acetaldehyde in alcohol fermentation, serves as the final electron acceptor.


(Image will be uploaded soon)


Image illustrating the flowchart of the fermentation process.


Facultative Anaerobes Examples

As we have seen the facultative anaerobe definition and the basis n which these classifications are made let us look into some examples. Enterobacteriaceae, Vibrionaceae, and Pasteurellaceae constitute the major families of facultative anaerobic bacteria. 

Facultative anaerobes examples from the Enterobacteriaceae family

  • E.coli

  • Klebsiella pneumoniae

  • Proteus mirabilis

  • Shigella

  • Salmonella

  • Yersinia pestis  

Facultative anaerobes examples from the Vibrionaceae family

  • Vibrio

  • Aeromonas

  • Photobacterium 

Facultative anaerobes examples from the Pasteurellaceae

  • Pasteurella and Haemophilus


Obligate Anaerobes vs Facultative Anaerobe

Since we have understood the facultative anaerobe, let us have a comparative study about the obligate anaerobes vs facultative anaerobe.


Difference Between Obligate Anaerobes vs Facultative Anaerobe

Facultative Anaerobe

Obligate Anaerobes

Can survive in both anaerobic and aerobic mediums.

Can survive only in the anaerobic condition

Energy production efficiency is high.

Energy production efficiency is low.

They do not die in presence of oxygen.

They die in presence of oxygen.

Obtain energy by aerobic respiration, anaerobic respiration, or fermentation.

Obtain energy either by anaerobic respiration or fermentation.

In a culture medium, they are spread throughout the test tube.

In a culture medium, obligate anaerobes are found at the bottom.

Examples include Staphylococcus spp,  Streptococcus spp,

Escherichia coli, Salmonella, Listeria,

Corynebacterium and Shewanella oneidensis.

Examples include Actinomyces, Bacteroides, Clostridium, 

Fusobacterium, Peptostreptococcus,

Porphyromonas, Prevotella, Propionibacterium, and Veillonella.


Ecological Importance of Facultative Anaerobes

Facultative anaerobes have played a critical role in the preservation and continuation of the global reserve of life's key elements, namely carbon, nitrogen, and sulphur, as well as the breakdown of complex molecules. Because facultative anaerobes can survive in a variety of environments, including those with and without oxygen. Alternative substrates for metabolism are used by these creatures, such as nitrogen, sulphur, and iron, which have all been part of various biogeochemical cycles on the planet that have led to the evolution of life, thus helping in the preservation of global resources. The facultative anaerobes are used as an alternative to producing biofuels, these organisms are also used in the process of water purification in the wastewater treatment process.  

In conclusion of the article, we have learned about facultative anaerobes, their definition example, and the mode of respiration. We have also learned about the difference between obligate anaerobes vs facultative anaerobe.

FAQs (Frequently Asked Questions)

Q.1 Is Enterococcus Faecalis Facultative Anaerobe?

Yes, Enterococcus faecalis is a facultative anaerobe. Enterococcus faecalis is a Gram-positive bacteria residing in the human gastrointestinal system in its normal state. Healthy humans have E. faecalis, which can be utilized as a probiotic. This organism belongs to the lactic acid bacteria (LAB) group, which can grow in a wide range of temperatures and have a low G+C concentration.

Q.2 Is Lactic Acid Bacteria Facultative Anaerobe?

Yes, lactic acid bacteria is a facultative anaerobe. The characteristic feature of these bacterias is to use a fermentative pathway for energy production. The pyruvate produced from glycolysis is converted into lactic acid, the net energy gain in this process is 2 ATP from a single molecule of glucose.


Q.3 What are the Key Characteristics of Aerobes?

The use of oxygen for survival is the key characteristic of aerobes. Aerobic bacteria or organisms undergo aerobic respiration that is they undergo oxidation of glucose in presence of oxygen to produce ATP. ATP acts as an energy currency that is required for cellular metabolism.

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