Aerobic bacteria require oxygen for respiration purposes. Without oxygen, there's no adenosine triphosphate (ATP) production; ATP provides energy to the cellular processes in the bacteria. Bacteria vary in the amount of oxygen needed to carry out chemical reactions. Some bacteria can only survive with the level of oxygen in the air; other bacteria prefer a lower amount. There are also bacteria which prefer oxygen, but can survive without it.
Strict Aerobes
A strictly aerobic bacteria has only one way to complete their energy metabolism---through oxidative phosphorylation. In this process, oxygen accepts electrons from the proton pump and becomes water. This reaction drives the phosphorylation, the addition of a phosphate group, of adenosine diphosphate (ADP) to ATP. Cellular processes throughout the body require energy to proceed, an energy provided by the ATP molecules. Without oxygen, no ATP gets created, and the cell processes fail to advance.
Some examples of strictly aerobic bacteria include Bacillus, Nocardia, Pseudomonas aeruginosa and Mycobacterium tuberculosis.
Facultative Anaerobes
Unlike strict aerobes, facultative anaerobic microorganisms can complete their energy metabolism in at least two different ways. In the presence of oxygen, facultative anaerobes use the oxygen as a final electron acceptor similar to strict aerobes; in the absence of oxygen, these bacteria begin to ferment sugars. In sugar fermentation, the final electron acceptor for energy production is the organic sugar molecule. Bacteria have specific sugars that they can and cannot ferment, and this varies by species.
Some of the most common facultative anaerobes include E. coli, Staphylococcus spp. and Listeria spp., among many others.
Microaerophiles
Microaerophiles require oxygen at a lower concentration than the concentration in the air. According to "Scientific American," Earth's atmosphere consists of 21 percent oxygen. This high oxygen percentage can be toxic to microaerophilic bacterial cells. Depending on the species, microaerophiles can require as low as one percent oxygen for optimal growth. These bacteria tend to find a place in the water column or deep in the soil where oxygen is present at a much lower level than on the surface.
According to Ohio State University, Borrelia burgdorferi, Helicobacter pylori, Lactobacillus spp. and Treponema pallidum exhibit metabolic requirements consistent with microaerophiles.
References
- "Microbiology: 6th Edition"; Lansing Prescott, John Harley and Donald Klein; 2005
- "Scientific American": The Origin of Oxygen in Earth's Atmosphere
- Ohio State University: Non-Nutrient Factors Affecting Growth
