Why is it necessary to adjust the pH to 7 4 7 6 before aliquoting the medium?

The preparation you are using is the commonly used beef paste peptone medium, in general, the preparation of the conditioning medium is based on the characteristics of the things you want to cultivate, and it is not static, if you want to cultivate a variety well, you can only slowly explore and gradually adjust the medium in order to achieve the best culture state.

As for the classic medium, like this recipe you mentioned, it's suitable for growing a lot of common bacteria, and it's often used in biology experiments, so you're required to know that it's in this range of pH.

And why it's in this range, it's because it's in this range, and it's suitable for growing a lot of common bacteria, and if you need to, you can go beyond that range and adjust your pH, for example, if you need certain substances that some bacteria produce when your pH doesn't adapt.

You're talking about peptone medium, which is mainly used to culture bacteria. pH to is only an approximate range and is suitable for most bacterial cultures. However, there are exceptions, such as acidophilus bacteria with extremely low pH.

In general, the adjusted pH is slightly higher than the optimal pH of the culture when preparing the medium. Because at the time of high sterilization, the pH value decreases. Some cultures have strict pH requirements, so they need to add buffers, which act like H2CO3 NAHCO3 in the human body, the front is acidic, and the back is alkaline.

Since the energy-supplying substances in our human body, such as sugar, are acidic after decomposition, such as pyruvate, this mechanism is described in high school biology textbooks. Buffers in the medium include PBS, Tris-Cl, etc.

A lot of the media is empirical, and many of the specific mechanisms are not very clear. Hope you understand.

It is very simple, it should be suitable for the growth of the cultivated microorganisms, but this pH is not fixed, and the optimal pH of different microorganisms is different.

pH is commonly used to indicate pH, and different types of edible fungi have their own pH range that can grow. Generally speaking, wood-rotting fungi are suitable for growing in acidic environments, while saprophytes prefer to grow in alkaline substrates. For example, Hericium erinaceus is pH3 4, shiitake mushroom and white fungus are pH5 6, fungus is ph4, and enoki mushroom can grow in the range of pH4 8, and the most suitable is pH6.

In the saprophytic mushroom of dung grass saprophyte, the mushroom is.

In order to make the prepared medium in the appropriate pH range, it should be considered: the nature and ratio of the culture material, the pH will be reduced after high temperature sterilization, the edible fungus will produce some organic acids in the growth process to reduce the pH, and the microbial activities of some culture materials in the process of composting and fermentation will also change the pH of the culture material. Therefore, if the culture material needs to be sterilized at high temperature, its pH should be slightly increased first.

In addition, in order to maintain the pH of the medium within the appropriate range during the culture process, a certain buffer is often added to the medium. Commonly used inorganic salts such as potassium dihydrogen phosphate (KH2PO4) and potassium hydrogen phosphate (K2HPO4) can not only provide edible fungi with phosphorus, potassium and other mineral nutrients, but also play a buffering role in pH changes. Calcium (Ca) not only neutralizes acidity, but also enhances the acid resistance of mycelium.

Because the pH of the environment required by different microorganisms is different, and the pH of the medium will also change due to the decomposition of nutrients and the accumulation of metabolites during the growth process of microorganisms, the pH of the medium needs to be adjusted during the configuration of the medium and in the process of microbial culture.

It should be noted that the biggest one is that the concentration of the bacteria will have a greater impact on the pH system, if the pH buffer used is slightly better, but it is still necessary to control the concentration of the bacteria, strictly speaking, in order to get very accurate results, the concentration of the bacteria needs to be controlled below 10 to the 6th power CFU ml, but it is difficult to achieve such a low concentration.

In general, NaOH is used for pH adjustment, and ammonia is not used very much, unless there is a special need. The specific scheme to use depends on the experimental protocol, and the effect of pH on the expression of genetically engineered bacteria should be studied with a buffer system, not just a simple adjustment of the initial pH.

1.Generally, the pH of the medium is measured with pH precision test strips

Cut a small piece of pH test paper with scissors, dip the medium to be measured with a glass rod, and measure the pH of the medium with a color palette at the same time. If the medium is acidic or alkaline, 1mol L NaOH or 1mol L HCl solution can be added slowly drop by drop, stirring while adding, and tested with pH test paper at any time until the desired pH is reached.

2.Precautions.

1) The medium must be cooled to room temperature before the pH can be adjusted

2) When adding acid or alkali solution, add a small amount slowly and stir more to prevent local over-acidity or alkali from destroying the nutrients in the medium.

3) Do not overadjust the pH, it is best to adjust it successfully at one time, otherwise it will affect the osmotic pressure of the medium.

4) When preparing the agar medium with low pH, if the pH is pre-adjusted and sterilized under high-pressure steam, the agar cannot be coagulated due to hydrolysis. Therefore, the components of the medium and the agar should be sterilized separately and then mixed, or sterilized at a neutral pH and then adjusted to pH.

5) Some microorganisms require more accurate pH, and the pH of the medium can be adjusted with an acidity meter

It is normal for the pH of the medium to change after sterilization and usually decreases, so you need to increase the pH slightly before sterilization. Of course, the change of pH after sterilization is different for different composition of the medium.

As for the reasons for the change in pH, it is more complicated, and there are many factors that can affect it. For example, the hydrolysis of which bond is the content of sugar, and the pH change of the medium with different sugar content. For example, when the medium contains a single component and when the medium contains high or high concentrations of substances, the pH value after autoclaving can change to more than 2 pH units.

The iron in the medium catalyzes the hydrolysis of sucrose when autoclaved, which can hydrolyze 15 -25 sucrose into glucose and fructose, which also affects the pH value, as well as the pressure effect. Etcetera.

Therefore, when adjusting the pH of the medium before sterilization, you need to budget and adjust the pH of the medium based on the experience of the pH changes of the medium that you have observed on a regular basis, because there is no empirical value that can be used for all media.

Summary. Determine 1 ml of medium to the sodium hydroxide used, + correct a total of 500 ml of medium, and use 300 ml of 1 20 n sodium hydroxide.

Measure 1 ml of medium to the sodium hydroxide used, + correct a total of 500 ml of medium, and use more.

Determine 1 ml of medium to the sodium hydroxide used, + correct a total of 500 ml of medium, and use 300 ml of 1 20 n sodium hydroxide.

Determine 1 ml of medium to the sodium hydroxide used, + correct a total of 500 ml of medium, and use 300 ml of 1 20 n sodium hydroxide.

To prepare the solution, add a part of the required amount of water to the container, weigh various raw materials according to the recipe of the medium, add them in turn to dissolve, and finally replenish the required water. For peptone, meat paste and other substances, it is necessary to heat and dissolve, and the water evaporated during the heating process should be supplemented with water after all the raw materials are dissolved. When preparing the solid medium, first boil the liquid medium that has been prepared above, then add the weighed agar, and continue to heat until it is completely melted.

And stir constantly so that the bottom of the agar paste does not burn. 2. Adjust the pH value with pH test paper (or pH potentiometer, hydrogen ion concentration colorimeter) to test the pH value of Jane Medium Medium, if it does not meet the needs, you can use 10% HCl or 10% NaOH to adjust until it is adjusted to the pH value required by the formula. 3. Filter filter paper, gauze or cotton while hot to filter the prepared medium.

When filtering with gauze, it is best to fold it into six layers, and when filtering with filter paper, the filter paper can be folded into a tile prismatic shape and spread on the funnel for filtration. 4. The filtered medium bench should be sub-packed. If you want to make bevel media, the medium must be aliquoted in test tubes.

If you want to make plate media or liquid, semi-solid media, the medium must be aliquoted in Erlenmeyer flasks. When dispensing, pinch and loosen the spring clip with one hand to let the medium flow out, and hold several test tubes or Erlenmeyer flasks with the other hand to pick up the medium in turn. When dispensing, be careful not to make the medium adhere to the mouth of the tube or the mouth of the bottle, so as not to soak the tampon and cause contamination by miscellaneous bacteria.

The amount of medium to be loaded into the tube, depending on the size and needs of the tube and Erlenmeyer flask.

During the culture process, the change curve of pH is related to the growth curve of microorganisms, from the beginning of culture, with the increase of microbial reproduction, the accumulation of metabolites accelerates, and the pH in the medium also shows a rapid change, whether it becomes acid or alkaline, which is related to specific microbial metabolites. Until the bacterial growth curve enters the decay period, the bacterial metabolism tends to stagnate, and the metabolites and nutrients in the medium no longer change due to the metabolism of microorganisms, and then the pH change decreases, and finally no longer changes.

The change of pH has a great impact on the culture of microorganisms, in practice, it is necessary to constantly monitor the change of pH, and use various means such as the addition of buffer system or aeration (oxygen or carbon dioxide or others) to stabilize the pH of the culture system in the good pH range, so as to achieve the purpose of microbial culture.

Before sterilization, it was adjusted with acid and alkali and tested with pH test paper. It will generally be higher than required, and autoclaving will make it drop a little. If it is filtered and sterilized, it can be adjusted directly to the specified value.

After all the components are configured, the pH is adjusted to the required level with NaOH and HCl, and the pH meter is used. Stir well.

Add acid and alkali.

Detected with a pH meter, which is usually higher than the pH needed, autoclaving will lower the pH