One of the most widespread and deeply studied prokaryotes is Escherichia coli. It is a gram-negative, symbiotic bacterium of the human body that performs protective and synthetic functions. However, it is fair to say that most serotypes are harmless, but O157:H7 can cause poisoning in humans. Escherichia coli lives in the distal intestine of most chordate animals, helping the body synthesize vitamin K and show protective functions against pathogenic bacteria.
For example, this prokaryote protects the body against Candida and putrefactive bacteria. In other words, as a rule, E. coli should be regarded as a natural symbiont of humans. The specificity of the habitat determines the metabolic properties of E. coli: it is a strict anaerobe, and optimal growth is possible at a temperature of 37°C. In addition, the bacterium forms succinate, acetate, and lactate as a result of its life activity, which is converted into the corresponding carboxylic acids in the presence of hydrogen. Since hydrogen ions prevent E. coli from obtaining the necessary salts, it is not uncommon for the bacterium to settle together with strains that consume hydrogen (Lu & Imlay, 2021).
Interestingly, E. coli is used to determine the possibility of fecal contamination of ecosystems since the natural escape of E. coli from an animal, or human body is only possible through defecation (Tousi et al., 2021). I used this link — (E. coli, 2018) — as a most helpful website because the credit rating of the information from the WHO is very high. The site gives a good overview of E. coli as a pathogen and as a symbiont and presents extensive guidelines. I learned that there is a specific STEC toxin that poses a danger from E. coli and also looked more closely at the list of possible sources of infection.
References
E. coli. (2018). WHO. Web.
Lu, Z., & Imlay, J. A. (2021). When anaerobes encounter oxygen: mechanisms of oxygen toxicity, tolerance and defence. Nature Reviews Microbiology, 1-12.
Tousi, E. G., Duan, J. G., Gundy, P. M., Bright, K. R., & Gerba, C. P. (2021). Evaluation of E. coli in sediment for assessing irrigation water quality using machine learning. Science of The Total Environment, 799, 1-13.