Generally speaking, the relationship between human beings and microorganisms is: mutual restriction, interdependence and dynamic balance.

Because on the one hand, microorganisms will cause food spoilage, cause a lot of losses in food industry production, cause diseases of people, animals and plants, and bring great disasters to mankind; On the other hand, they can benefit mankind and are extremely beneficial to human life and production. For example, microorganisms can be used to make fertilizers, feed, food, medicines and chemical raw materials.

Microbial reproduction:

Compared with large animals, microorganisms have a very high growth and reproduction speed. Escherichia coli can reproduce 12.5-20 minutes/time. Let's calculate, 1 Escherichia coli divided by 1 times in 20 minutes, 1 hour divided by 3 times, 1 day and night divided by 24 times = 72 times, which can produce about 472,236,500 trillion (72 power of 2), which is a very huge number.

But in fact, due to various conditions, such as lack of nutrition, intensified competition, deterioration of living environment and other reasons, microorganisms can not fully achieve this exponential growth. It is known that the optimum pH range of most microorganisms is around 7.0 (6.6~7.5), and some of them are below 4.0.