Microbial growth and its control

MindMap Gallery Microbial growth and its control

Microbial growth and its control

This is a mind map about the growth and control of microorganisms, including microbial measurement, microbial growth patterns, Lactic acid fermentation and alcoholic fermentation, etc.

Edited at 2023-11-29 12:37:55

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Microbial growth and its control

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Microbial growth and control

Microbiological measurements

Dilution plate method: soil sample dilution - shaking - gradient dilution - culture (pour the culture medium and spread it - coating method; pour the bacterial liquid into the agar medium and mix it - pouring method)

Pour method: Both aerobic and anaerobic bacteria can be separated.

Coating method: Use 1 ml for coating to isolate actinomycetes.

Question: Why can’t too much bacterial solution be used in the coating method? Answer: In order to separate and count, we added too much liquid and mixed them together. We should use 0.1 ml.

The plate streaking method (three-zone streaking) requires burning and sterilizing the first streak, and then drawing again, aiming to form a single colony. A single colony is called a pure colony.

Problem: The pure bacterial colonies appear to have the same shape, but the metabolic functions of the bacteria inside are not very good. In the fermentation industry using single colonies, the metabolic characteristics will change, and the bacteria with low productivity may become dominant bacteria. How to restore high productivity in this situation? Answer: Most of the bacteria in the sample are declining bacteria, and a small number of bacteria have good metabolic functions. Use selective culture. If the samples are degraded this time and there are no good bacteria, use the mutagenesis method (the conditions of temperature, light, water and vapor: ultraviolet mutagenesis) to rejuvenate the bacteria.

Indirect separation method: measuring microorganisms, as well as physiological indicator methods and turbidimetric methods.

Question: In what situations is turbidity method better to use? Answer: Translucent (bacteria, yeast), bacteria that sink to the bottom are not easy to use. Bacteria that disperse after growth are easy to use, bacteria that die after growth are not easy to use, and bacteria that grow into agglomerates are not easy to use. If it is mold, look at the amount of mycelium, dry the mycelium and measure the weight.

The growth pattern of microorganisms

slow period Characteristics: The growth rate constant is zero, the bacteria are thick, the RNA content is increased, the metabolic activity is strong, and the resistance to adverse environments is reduced. Cause: The microorganism has just been inoculated onto the culture medium, and its metabolic system needs to adapt to the new environment and synthesize enzymes, coenzymes, and other metabolic intermediate metabolites, so the number of cells does not increase during this period.

Logarithmic period Characteristics: The fastest growth rate, vigorous metabolism, active enzyme system, the number of viable bacteria and the total number of bacteria are roughly close, and the chemical composition, morphology, and physical and chemical properties of the cells are basically the same. Cause: After the preparation of the adjustment period, sufficient material basis is provided for the growth of microorganisms during this period, and the external environment is also in the best state.

stable period Features: The number of viable bacteria remains relatively stable, the total number of bacteria reaches the highest level, the accumulation of cell metabolites reaches the highest peak, it is the harvest period of production, and Bacillus begins to form spores. Cause: The consumption of nutrients leads to imbalanced nutrient proportions, accumulation of harmful metabolites, unsuitable physical and chemical conditions such as PH value and EH value.

period of decline Characteristics: The death rate of bacteria is greater than the rate of new generation, the entire population experiences negative growth, cells begin to become deformed, and cell death occurs with autolysis. Cause: The main reason is that the external environment is becoming more and more unfavorable for continued growth, and the catabolism of cells is greater than anabolism, which in turn leads to the death of a large number of bacteria.

Lactic acid fermentation and alcoholic fermentation

Lactic acid fermentation occurs in both animal microorganisms and plant alcoholic fermentation. When we run like crazy, we produce a lot of lactic acid, and a person's lactic acid tolerance determines how fast or slow they run. Lactic acid and pyruvate are converted into each other. Northeastern sauerkraut, Korean kimchi, spicy cabbage all have lactic acid bacteria. Acid-resistant and bile-resistant lactic acid bacteria. Fungi produce lactic acid and have lactate dehydrogenase, and some cancer cells can use lactic acid. If a person's lactate dehydrogenase is not good, lactic acid will not be degraded and lactic acidosis will occur. Analysis: Lactose is converted into lactic acid using β-galactosidase. E. coli in the intestine has this enzyme. This enzyme in humans is induced. In addition to inducible enzymes, there are also housekeeping genes - constitutive enzymes.

Question: Why was a classmate able to drink milk when he was a child, but suddenly couldn’t drink it in high school? Answer: Human milk oligosaccharides will screen out beneficial bacteria. Lactose intolerance is when the body has adapted to other nutritional sources, so you can practice it every day.

Question: Why doesn’t sauerkraut rot? Answer: Lactic acid bacteria only decompose sugar and not cellulose.

Question: What are the bacterial strains on yogurt, such as Bifidobacterium, etc., what are the differences between these bacteria?

Growth curve, take an example, design an experiment, how to draw a growth curve? If you can design experiments in this way, you can become a graduate student.

The growth curve is the logarithm of the amount of bacteria, because bacteria grow exponentially. The first step is to adapt to the environment - the lag phase, and then enter the logarithmic growth phase after adaptation (the bacterial growth cycle is the same, which is very rare, and there is a certain mechanism between bacteria to inform each other). Why does it enter the stable phase after the waiting formula? After 10 vaccinations and a delay period of 1 hour, 320 were detected. How long will it take? The number of bacteria does not increase during the delay period, and is reduced by 1 in the end.

Question: If we get a strain of lactic acid bacteria that can withstand oxygen and survive in the human body for a long time, what should we do if the company asks us to get this strain of bacteria, which involves the laws of growth and reproduction? Question: The boss asked at which point in the growth curve to harvest this bacteria? Answer: The point before the stationary period and after the logarithmic period. Question: The company wants to produce drugs or enzymes? Answer: It needs to be a point after the stable period and before the decline period.

Question: If it is diluted to a certain level and the bacteria no longer grow, but microscopic examination shows that the bacteria are still there, will the bacteria still grow if the medium is replaced with a particularly good medium? Raising doubts, does it mean that if it is diluted to one cell, it will no longer grow? Answer: We underestimated the number of bacteria examined.

Question: If microorganisms are cultured, how to conduct relevant research and how to measure the number and size? How is microbial reproduction measured? Answer: direct counting (microscope, counting viable yeast with Meilan staining), indirect counting (pure species that can be cultivated can use the dilution plate method, and the sample is a mixed bacteria), gravimetric method.

Combining theory with practice: a task, detecting which soil microorganisms are related to national secrets? Answer: There are strain collection centers in the world, and trading between institutions does not involve state secrets. If you go to Xinjiang and Tibet in my country to ask for soil samples, there are no scientific research units, so it may be espionage. 99% of the microbial resources in the soil have unclear functions. If used properly, they are very large resources.