Pure cultures are the key dogma of microbiology in the 20th century. To understand the essence of this concept, it is worth remembering that bacteria are very small and morphologically difficult to distinguish. But they differ in biochemical processes, and this is precisely their main species feature. But in a normal environment, we are not dealing with one type of bacteria, but with a whole biome - a community that influences each other, and it is impossible to single out the role of one microorganism. And this is where we need a pure culture or strain of a particular species.
Microbe Hunters and agar-agar
The ingenious idea of isolating pure cultures of microbes belongs to the medical microbiologist Heinrich Hermann Robert Koch (1843-1910). The one who discovered the causative agent of anthrax, cholera and tuberculosis and is deservedly considered the founder of bacteriology and epidemiology.
He's the oneinvented the method of pure cultures, when a diluted culture of microbes is applied to a nutrient medium based on agar-agar polysaccharide and a colony of completely identical organisms grows from one cell. It is clearly visible to the naked eye and is specific to each species.
His invention gave impetus to the development of microbiology and taxonomy of microorganisms. After all, it was possible to cultivate any microbe in its pure form and examine one hundred million cells as one.
Without diminishing Koch's accomplishments
It is worth noting that Koch's associates and students contributed to this invention. So, the idea of using agar-agar belongs to Fanny Angelina Hesse, the wife of Koch's assistant, W. Hesse.
Another assistant to Koch, the bacteriologist Julius Richard Petri (1852-1921), suggested growing colonies of bacteria in flat glass dishes. Today, even schoolchildren know about Petri dishes.
Dogma of microbiology
Pure (ascenic) culture - a set (population or strain) of microorganisms that have identical morphological and biochemical properties and are descendants of one cell.
Isolation of a pure culture involves the implementation of three stages:
- Obtaining and accumulating the culture of microorganisms.
- Isolation of pure culture.
- Determination and verification of culture purity.
Pure culture isolation methods
In microbiology, the following methods are used to obtain axenic cultureorganisms:
- Mechanical methods (inoculation on Petri dishes with a spatula or loop, inoculation by agar dilution - plate spreads, separation method based on microorganism motility).
- Biological - a method in which laboratory animals susceptible to a pathogen are infected. This is how pure cultures of bacteria are isolated from the body of mice (for example, pneumococci and tularemia bacilli).
- Methods based on the selective resistance of microorganisms to certain factors. When heated, for example, all spore-forming bacteria will die, while non-spore-forming bacteria will remain in pure culture. When exposed to acids, bacteria that are sensitive to them die, while acid-resistant ones (for example, tuberculosis bacilli) survive. The impact of antibiotics leaves on the medium a pure culture of microorganisms that are not sensitive to it. Creating an oxygen-free environment will separate aerobes from anaerobes.
What is it for
Pure cultures apply:
- In scientific taxonomy when classifying (determining the phylogenetic place in the system) microorganisms.
- In the study of heredity and variability of organisms.
- In infectious diagnostics and detection of pathogens.
- When isolating a pure culture of bacteria that lead to food spoilage.
- In the production of vitamins, enzymes, antibiotics, serums and vaccines.
- In the food industry (production of bread, wine,kvass and beer (acetic bacteria and unicellular fungi yeast), lactic acid products (lactobacilli and lactic acid bacteria)).
- In biotechnology and in the study of viruses.
In nature, everything is completely different
In the 90s of the last century, everything suddenly changed with respect to pure cultures. It turned out that when microorganisms of two pure strains are combined in one test tube, they behave quite differently than they do alone. The biochemical processes of their vital activity influence (suppress or stimulate) each other. This is exactly what happens in natural biomes.
The conclusion is simple: the properties of pure culture in the laboratory cannot be extrapolated to natural biomes.
Genomic Revolution
Another blow has been de alt by the genomic identification of microorganisms. Initially, for the genomic analysis of microorganisms, molecular geneticists chose a region of ribosomal RNA common to all bacteria. In accordance with the differences in the nucleotide sequence in this nucleic acid, all bacteria were distributed on the basis of phylogenetic relationship.
That's when it turned out that cultured strains and those bacteria that we studied make up about 5% of all bacteria inhabiting our planet. And, unlike cultural strains, we know nothing about their properties and biochemistry.
Having found the corresponding sequence in the genome of a natural strain, we can only place it on the phylogenetic tree andassume that in nature it has the same properties as the closest related strain of a pure line.
And what's next?
Sequencing of the bacterial genome from a single cell is still in the future. Today, while it is expensive and very difficult. And so pure lines remain the "golden reserve" of microbiology.
Though the difficulties remain. For example, the bacteria of "black smokers" located at the bottom of the ocean have recently been studied. The microorganism was described and its genome sequenced without isolating a pure culture.
A similar situation exists with bacteria living in the depths of gold mines. It turned out that this is a pure line of microorganisms - the descendants of one bacterium.
However, these organisms do not grow on nutrient media, and so far no one has succeeded in growing a colony of a pure strain.
Biotechnology News
Mankind faces many questions in the development of this branch of applied knowledge. And not only biological, but also ethical. To what extent can a person change the world around him and not harm it? The question remains open.
But today biotechnology is being introduced into our lives. So, strains of bacteria that are able to feed on plastic and decompose it have already been bred. As long as they do it slowly. But scientists are working on their genome. No one is surprised that all human insulin is "made" by genetically modified E. coli bacteria.
A artificial biosynthesisalready today supplies us with biogas and biofuels in the form of high-molecular carbohydrates of natural origin (the waste products of bacteria, protozoan fungi that process the biomass of our waste into fuel, energy, chemicals).
Arable land and fresh water are today the most important component of limited natural resources. New biotechnologies (bioremediation) offer the possibility of using microorganisms to restore their potential and remove pollutants.
And that's it - the future is already here.
