8
O
Oxygen
15.999
Essential: all life
Oxygen
Environmental and health impacts:
- Climate change is causing drop in ocean oxygen levels
-Deforestation causing decrease in atmospheric oxygen levels
Reduce:
- Many organisms (anaerobes) can live without molecular oxygen (O2), and can grow by either fermentation or anaerobic respiration. However, these cells still require atomic O as an essential element.
- Bacteria in biofilms deplete O2, and may then use phenazines and alternate terminal oxidases (2) in place of aerobic respiration.
-Switch from aerobic to anaerobic metabolism (3)
Learn More!
(1) Oxygen: Essential for All Life
Oxygen is essential for all organic molecules because it is one of the elements that makes up water, and all life is based in aqueous chemistry. Water is both the universal solvent for biochemical reactions and an active participant. Water is incorporated in molecules by both hydrolysis and hydration reactions and is generated as a product during dehydration-based syntheses.
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Molecular oxygen is needed for aerobic respiration in many species from all domains of life. O2 is the terminal electron acceptor in the electron transport chain, which is the final stage of aerobic respiration.
(2) Oxygen Limitation in Biofilms
Bacteria often live in biofilms, but as the community grows, the cells have to compete for nutrients, and oxygen often becomes limited. Some bacteria in biofilms, such as P. aeruginosa, have evolved several strategies to respond to these low oxygen conditions (Jo, et al., 2017).
1. Change the structure of the biofilm to increase the surface area-to-volume ratio, which allows more bacteria to be on the outside and more easily access oxygen.
2. Synthesize phenazines, which move electrons to the outside of the cell, where oxygen is present
3. Synthesize alternate terminal oxidases that are more efficient at utilizing or capturing oxygen. Cells in low-oxygen conditions rely on the terminal oxidase protein CcoN4 to scavenge for oxygen in order to grow.
(3) Aerobic to Anaerobic Respiration
Though elemental oxygen is rarely limiting because it is found in water, molecular oxygen is incredibly limiting for all animals that need O2 for aerobic respiration. Though oxygen is the most efficient terminal electron acceptor, many organisms have developed mechanisms to survive in low oxygen conditions. Facultative bacteria, such as Staphylococcus spp., Streptococcus spp., E. coli, Salmonella, and Listeria spp., are capable of changing their metabolism from aerobic to anaerobic respiration under oxygen limitation (Shan, et al., 2012). Certain eukaryotes also have this ability, including fungi like S. cerevisiae and some aquatic invertebrates. In animals, though the entire metabolism of the body does not change, muscle cells use anaerobic respiration during periods of intense physical activity.