Microbes seem to thrive in anaerobic conditions rather than aerobic ones

The notion that microbes thrive more in anaerobic conditions than in aerobic ones is not entirely accurate and requires a nuanced examination based on the diversity of microbial oxygen requirements. Microbes, particularly bacteria, exhibit a wide range of adaptations to different oxygen levels, and their ability to thrive depends on their specific metabolic needs and environmental conditions.

• Diversity of Oxygen Requirements: Bacteria display significant variation in their response to oxygen. Obligate aerobes, such as Bacillus subtilis and Pseudomonas aeruginosa, require oxygen for growth, using it as the final electron acceptor in aerobic respiration to produce energy efficiently123. In contrast, obligate anaerobes, like Clostridium species, cannot survive in the presence of oxygen, as it can poison their metabolic processes; they rely on fermentation or anaerobic respiration for energy142. This shows that neither condition is universally preferred—success depends on the microbe's physiology.

• Facultative and Tolerant Variants: Many microbes are not strictly bound to one condition. Facultative anaerobes, such as Escherichia coli and Staphylococcus aureus, can switch between aerobic respiration (more efficient for energy production) and fermentation or anaerobic respiration depending on oxygen availability, often growing better with oxygen present142. Aerotolerant anaerobes, like certain lactobacilli, do not use oxygen but can tolerate its presence without harm, while microaerophiles, such as Campylobacter jejuni, require low oxygen levels (1-10%) and are harmed by atmospheric concentrations (21%)23. This adaptability suggests that thriving is context-dependent rather than skewed toward anaerobic conditions.

• Environmental Distribution: Anaerobic microbes are often found in oxygen-deprived environments like deep soil, digestive tracts, marshes, and the sea floor near hydrothermal vents, where they generate energy through processes like fermentation or chemosynthesis425. Aerobic microbes, however, dominate in oxygen-rich settings such as surfaces and water bodies4. The presence of anaerobes in specific niches does not indicate a general preference for anaerobic conditions but rather reflects specialized adaptations to those environments.

• Metabolic Efficiency and Toxicity: Aerobic respiration typically yields more energy (ATP) than anaerobic processes like fermentation, which is why facultative anaerobes often grow better with oxygen42. However, oxygen can produce toxic by-products such as superoxide and hydrogen peroxide, which aerobic organisms counteract with enzymes like catalase and superoxide dismutase. Many anaerobes lack these enzymes or have limited capacity, making oxygen harmful to them12. This toxicity might give the impression that anaerobic conditions are more favorable, but it is specific to certain microbes rather than a universal trend.

• Experimental Observations: In thioglycolate tube cultures, which test oxygen requirements, obligate aerobes grow at the top (high oxygen), obligate anaerobes at the bottom (no oxygen), and facultative anaerobes mostly at the top but throughout, indicating a preference for oxygen when available. Microaerophiles cluster in a middle zone with just the right oxygen level, and aerotolerant anaerobes are evenly distributed, unaffected by oxygen presence23. These patterns demonstrate that microbial growth is highly variable and not predominantly anaerobic.

In conclusion, microbes do not universally thrive more in anaerobic conditions. Their success is determined by their specific oxygen requirements and the environments they inhabit. While anaerobic microbes are well-adapted to oxygen-free zones, many others depend on or prefer oxygen for efficient energy production. The perception that anaerobic conditions are more favorable may stem from the prevalence of anaerobes in certain extreme or niche environments, but across the microbial world, both aerobic and anaerobic conditions support thriving populations based on individual adaptations.

1. https://www.britannica.com/science/bacteria/Physical-requirements
2. https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(OpenStax)/09:_Microbial_Growth/9.02:_Oxygen_Requirements_for_Microbial_Growth
3. https://jackwestin.com/resources/mcat-content/growth-and-physiology-of-prokaryotic-cells/existence-of-anaerobic-and-aerobic-variants
4. https://www.cd-genomics.com/microbioseq/what-is-the-difference-between-aerobes-and-anaerobes.html
5. https://en.wikipedia.org/wiki/Anaerobic_organism
6. https://www.ncbi.nlm.nih.gov/books/NBK482349/
7. https://study.com/learn/lesson/aerobic-vs-anaerobic-bacteria-overview-differences-functions.html
8. https://medlineplus.gov/ency/article/002230.htm
9. https://www.sciencedirect.com/topics/engineering/anaerobic-condition
10. https://en.wikipedia.org/wiki/Anaerobic_infection