1, concept

Growth: microorganisms absorb nutrients and metabolize under suitable environmental conditions, and the cellular components of organisms grow in a coordinated and balanced manner.

Reproduction: a biological process that leads to an increase in the number of individuals.

Pure culture: offspring obtained by reproduction of a cell or a group of cells under laboratory conditions.

2, the growth law of microorganisms

The "growth" mentioned in microbiology refers to group growth.

Growth curve: Inoculate bacteria into quantitative liquid culture medium, and take samples at regular intervals to determine the number of cells. Taking the culture time as the abscissa and the number of bacteria as the ordinate, a curve reflecting the change law of the number of bacteria during the whole culture period was obtained.

The growth curve of bacteria is generally plotted with the logarithm of the number of bacteria as the ordinate.

A typical growth curve can be divided into at least four growth periods: slow period, logarithmic period, stable period and declining period.

Characteristics of lag period:

(1) Cell morphology becomes larger or grows, such as Bacillus megaterium. At the end of the lag period, the average length of cells is six times that of the cells just inoculated. Generally speaking, the bacterial cells in the lag phase have the largest volume;

(2) The content of intracellular RNA, especially r RNA, increased;

(3) The anabolism is active, the synthesis of ribosomes, enzymes and ATP is accelerated, and it is easy to produce induced enzymes;

(4) Sensitive to external unfavorable conditions.

The reason of lag period: regulating metabolism

When microorganisms are inoculated into a new environment, they temporarily lack enzymes that decompose and catalyze related substrates, or lack sufficient intermediate metabolites. In order to produce induced enzymes or synthesize intermediate metabolites, an adaptation period is needed.

Common means to shorten the lag period in production practice;

(1) Change the genetic characteristics of species through genetic methods and shorten the lag period;

(2) taking cells in logarithmic growth period as seeds;

(3) Try to make the composition of the medium used before and after inoculation little different;

(4) Appropriately expand the inoculation amount.

Factors affecting microbial generation time (generation time);

1) strain, different microorganisms and different strains of microorganisms have different generations;

2) nutrient components, and the growth time in nutrient-rich culture medium is short.

3) Nutrient concentration, within a certain range, the growth rate is directly proportional to the nutrient concentration.

4) Temperature, in a certain range, the growth rate is positively correlated with the culture temperature.

The stable growth period is also called constant period or maximum growth period, when the number of viable bacteria in the culture medium is the highest and remains stable.

Fading period:

With the depletion of nutrients and the accumulation of toxic metabolites, the mortality rate of bacteria exceeded the newborn rate, and the whole population showed negative growth.

The metabolic activity of bacteria decreases, bacteria age and autolysis occurs, producing or releasing some products, such as amino acids, invertase, exopeptidase or antibiotics. Cells show various shapes, sometimes deformed, and the cell size varies greatly, and some Gram-positive bacteria become negative.

During this period, the number of dead bacteria increased logarithmically, but in the later period of decline, the death rate of bacteria also decreased, because some bacteria developed drug resistance and some live bacteria still existed.

Endogenous respiration: when the nutrients in the environment are exhausted, microorganisms begin to use their own storage and even bacterial components as nutrients to maintain their lives. This is called endogenous metabolism or endogenous respiration.

Secondary growth phenomenon:

Different microorganisms or the same microorganism have different utilization abilities for different substances. Some substances can be directly used (such as glucose or NH+4). ); Some need to go through a certain adaptation period to gain utilization ability (such as lactose or NO3-). The former is usually called available carbon source (or nitrogen source), and the latter is called delayed carbon source (or nitrogen source). When both carbon sources (or nitrogen sources) are contained in the culture medium, microorganisms will form a secondary growth phenomenon during their growth.

3. Cultivation methods of microorganisms

(1) Batch culture: the microorganisms are placed in a certain volume of culture medium, cultured and grown, and finally harvested.

The culture medium is added at one time, and there is no need to supplement and replace it.

Batch culture cannot be maintained in logarithmic growth period.

(2) Continuous culture: a culture method in which microorganisms grow at a constant specific growth rate and continue to grow in some way during the whole culture period.

It is the basic principle to constantly supplement nutrients and remove the culture at the same speed during the culture process.

(3) semi-continuous culture

(4) fed-batch culture

(5) Synchronous culture: make the cells in the population in a relatively consistent state, and their growth and development are at the same stage, that is, most cells can grow or divide at the same time.

Synchronous growth: Population cells can be in the same growth stage through synchronous culture and can divide and grow at the same time.

Cells obtained by synchronous culture are called synchronous cells or synchronous cultures.

4. Influence of environmental factors on microbial growth

nutrient

temperature

High temperature denatures and destroys important biological macromolecules such as protein and nucleic acid, destroys lipid components on cell membrane, and leads to microbial death.

Low temperature inhibits the growth of microorganisms, but generally does not lead to microbial death.

Wet heat sterilization is better than dry heat sterilization;

Easier heat transfer;

It is easier to destroy hydrogen bonds and other structures that maintain protein stability;

Patient History

Oxygen and redox potential

Water activity and osmotic pressure

radiation

Radiation sterilization is an effective method to kill microorganisms on most substances by using electromagnetic waves generated by electromagnetic radiation.

supersonic

chemical agent

chemotherapeutant

Physical and chemical factors related to bacteriostasis or sterilization;

(1) strength or concentration of physical and chemical factors;

(2) the duration of the same concentration of physical and chemical factors;

(3) Different kinds of microorganisms;

(4) Different growth periods of the same microorganism.

disinfectant

(1) Non-selective (toxic to all cells): widely used for sterilization of some heat-sensitive articles or places that cannot be sterilized at high temperature.

A. Disinfectants

Carbonic acid, the earliest disinfectant used in clinic.

Carbonic acid coefficient:

Refers to the highest dilution that the test preparation can kill all the tested bacteria in a certain period of time.

And the highest dilution ratio of carbolic acid with the same effect. The general treatment time is 10 minute, and the bacteria detected are Salmonella typhi.

B. preservatives

(2) selectivity (more toxic to pathogenic microorganisms):

A. antimetabolic drugs

Sulfonamides are the earliest and most common chemotherapeutic drugs, which have a wide antibacterial spectrum and can treat many infectious diseases.

The bacteriostatic effect of sulfanilamide is because many bacteria need to synthesize folic acid themselves to grow.

B. antibiotics

Concept: It is a kind of secondary metabolites or derivatives synthesized or semi-synthesized by some organisms, which can inhibit or affect the life activities of other organisms at very low concentrations, such as killing microorganisms or inhibiting their growth.

Characteristics of drug-resistant strains:

(1) The permeability of plasma membrane changes, so that antibiotics do not enter cells or are actively excreted by cells after entering cells;

(2) Changes in drug targets;

(3) Synthesizing enzymes for modifying antibiotics;

(4) The genetic variation of drug-resistant strains leads to the synthesis of new polymers, replacing or partially replacing the original polymers;

Measures to avoid drug resistance of bacteria;

(1) The dosage of drugs used for the first time should be sufficient;

(2) Avoid using the same antibiotic for a period of time or for a long time;

(3) Use different antibiotics (or mix them with other drugs);

(4) Reforming the existing antibiotics;

(5) Screening new and more effective antibiotics;

C. effective components of Chinese herbal medicines

Metabolism of microorganisms

Heterotrophic microorganisms use organic substances, while autotrophic microorganisms use inorganic substances to metabolize their productivity through biological oxidation.

Matrix (substrate) level phosphorylation:

In the process of oxidation, some high-energy compound intermediates containing more free energy than ATP hydrolysis will be produced. This high-energy substance can directly give ADP bond energy to phosphorylate and generate ATP.

Electron transfer phosphorylation:

During the oxidation process, the electrons released by the substrate are transferred to the acceptor through the electron transfer chain, and the energy is gradually released during the transfer process to generate ATP.

The fundamental difference between respiration and fermentation;

The electron carrier is not an intermediate product that directly transfers electrons to the substrate, but is handed over to the electron transfer system, which gradually releases energy and then gives it to the final electron acceptor.

Pasteur effect: If facultative anaerobic microorganism has O2 in the fermentation process, it will have the effect of respiration inhibiting fermentation, which is called Pasteur effect.

light

Photophosphorylation, like oxidative phosphorylation, produces ATP through electron transfer system.

Phototrophic organisms:

Oxygen production: eukaryotes: algae and other green plants; Prokaryote: cyanobacteria

Non-oxygen producing: photosynthetic bacteria (only in prokaryotes)

P870 is the reaction center of photosynthesis that does not produce oxygen.

Chlorophyll-free or bacterial chlorophyll-free photosynthesis in halophilic bacteria.

Unique photosynthesis

The photophosphorylation of purple membrane is the simplest photophosphorylation reaction found so far.

Nutrient decomposition

Decomposition of monosaccharides:

Metabolic pathway: 1. Electromagnetic pulse path II. HMP pathway 3. ED pathway 4. 5.HK way.