A: Obligate aerobic (need oxygen) bacteria mainly grow in the upper part of the tube in order to absorb the maximum amount of oxygen (excluding mycobacteria: grows like a film on the surface). B: obligate anaerobic bacteria grow in the bottom of the tube, to avoid oxygen (in the presence of oxygen they cannot grow). C: Facultative aerobic and anaerobic bacteria grow over the entire area of ​​the tube, but collect mainly at the top (oxidative-phosphorylation is more beneficial than glycolysis). They are able to switch metabolism from breathing to fermentation. D: Aerotolerant anaerobes do not depend on oxygen concentration, and are evenly distributed throughout the tube. E: Microaerophiles grow at the top of the tube, but their optimum is low oxygen concentration. In the last lecture we spoke about
The physiology of microorganisms. Bacterial metabolism
The basis of the vital activity of microorganisms, as well as all living beings, is the exchange of substances with the environment –metabolism (consumption of substances from the environment, splitting, synthesis, release
into the environment).
For microorganisms inhabiting the human body, the environment is the skin and mucous membranes of the human body (the main habitats of the human microbiome).
Peculiarities of bacterial metabolism:
-high intensity of metabolic processes;
-catabolic processes prevail over anabolic processes bacteria are able to assimilate a variety of inorganic and organic substances (substrates)
-bacteria have a very large set of different enzymes.
In biochemistry, a substrate is a substance that is converted into one
or more final products as a result of interaction with an enzyme
(For example: glucose is converted into pyruvic acid by a complex of enzymes)
Constitutive enzymes
Inducible enzymes
Exoenzymes
Endoenzymes
Oxidoreductases
Ligases
Lyases
Isomerases Transferases
Hydrolases
Enzymes of microorganisms
а) digestive enzymes б) protective enzymes; c) aggression enzymes Methods for detecting the saccharolytic properties of bacteria.
To determine the saccharolytic properties the following media are used: dense Endo, Levin and Ploskirev media, as well as liquid and semi-liquid Giss media.
Methods for detecting proteolytic properties of bacteria.
The proteolytic properties of bacteria study:
according to the ability to dilute gelatin: different types of bacteria have different forms b) according to the final products of protein breakdown after inoculation for meat-peptone broth (MPB). Transport of substances into the bacterial cell
Substances can enter the cell in the following ways:
Passive diffusion Active transport. Symport Antiport
Transport of substances from a bacterial cell
An one-stage system - a single pore (channel)
A two-stage transport system - proteins pass through the inner and outer membranes in separate stages. The energy received by the cell during respiration or fermentation
is used for the growth and reproduction of bacteria.
Growth is an increase of the mass of a single cell, it is a result of synthetic processes. During growth the cell size is getting bigger. Having reached a certain size, the cell stops growing and begins to divide (reproduce itself).
Bacterial growth and reproduction
Under favorable conditions most microorganisms divide every 20-30 minutes. At this rate of division 1024 specimens are formed from one microorganism in 5 hours.
The reproduction of bacteria is carried out on nutrient media
containing the necessary components, under optimal temperature conditions, with a certain oxygen saturation
of the medium.
Reproduction is characterized by:
1 - generation time – the time interval during which the number of cells doubles;
2 - the concentration of bacteria - the number of cells in 1 milliliter.
Lecture 4
The physiology of microorganisms. Reproduction. Growth (cultivation).
Asexual reproduction of bacteria – the ability of bacteria to reproduce themselves (increase the number of specimens). The majority of bacteria
are characterized by binary transverse division, leading to the formation of two identical daughter cells.
The division of a bacterial cell begins when the replication of the bacterial
nucleoid (chromosome) is complete. Then a transverse septum is formed in the middle part of the cell, which divides the cytoplasm of the mother cell into two daughter cells. At the same time a cell wall is synthesized, forming a full-fledged septum between two daughter cells.
Some microorganisms reproduce themselves by budding. This method is a characteristic of yeast.
Bacterial cells dividing
yeast
Mechanisms of transmission of genetic material
In addition to the main mechanism of gene transfer — by inheritance (vertically),
bacteria can exchange genetic material horizontally, that is between single specimens in a population of cells.
Bacteria have several mechanisms of transmission of genetic material
: transformation, transduction, transfection, conjugation.
1.Transformation is the process of changing the properties of some microorganisms under the influence of the DNA of other microorganisms. Transformation is the ability of a bacterial cell to absorb DNA molecules from the extracellular (surrounding) environment. The transformation process was discovered in 1928 (nineteen twenty-eight) on the culture Streptococcus pneumonia. It turned out that when the killed virulent pathogens met live non-virulent streptococcal cells, the living ones acquire the ability to cause the disease. The recipient cell is able to perceive other DNA if it is in a certain physiological state of "competence". Competent cells have a reduced level of metabolism, changed cell surface, they become more sensitive to the osmotic shock. Not only chromosomal, but also plasmid and phage DNA can transform cells. Interspecific transformation is also possible.
Transformation can be spontaneous or induced. Induced (artificially obtained) transformation occurs when purified DNA is added to the bacterial culture. This purified DNA is obtained from the cultures of those bacteria that tend to transfer genetic characteristics to the study culture. Spontaneous transformation occurs under natural conditions.
2. Transfection is a variant of transformation of bacterial cells deprived of a cell wall. It is carried out by the nucleic acid of the virus (bacteriophage). With the help of transfection, the DNA of the virus enters the bacterial cell (without a cell wall). Transfection can also be performed with other (non-bacterial) cells.
4.Transduction (from Latin transductio-moving) is a transfer of genetic material from a donor cell to a recipient cell with the help of bacteriophages. It leads to a change in the hereditary properties of recipient cells. Phages accidentally capture a fragment of a nucleoid (1-2% one-two percent of the bacterial genome) during cell lysis and the formation of mature phage particles. This is a non-specific transduction — the random transfer of DNA fragments from one bacterial cell to another.
Specific transduction is carried out only by carried phages that have the ability to be included in strictly defined sections of the bacterial cell chromosome and to transduce certain genes.
Electron microscopic image of the conjugation in Escherichia coli; elongated cell - donor,
round - recipient 4.Conjugation — (from Latin conjugatio — connection), is the process of exchanging genetic material (chromosomal and plasmid), carried out by direct contact of the donor and recipient cells. The transfer is carried out with the help of pili.
Reproduction and growth of microorganisms during cultivation on an industrial scale
Reproduction of bacteria is studied during cultivation in liquid
or dense nutrient media. In a liquid nutrient medium cultivation can be continuous or periodic. For the production of bacterial biomass,
when obtaining vaccines, antibiotics, and medicine for
normal flora, cultivation is used in cultivator devices. There are continuous and periodic cultivation.
During continuous cultivation an open system is used, that is,
it is possible to supply / add fresh nutrient medium and
to remove accumulated biomass or metabolites from the
cultivator (fermentor) machine.
During periodic cultivation nutrients are not introduced
into the system additionally, and metabolic products are
not removed. In this case, the reproduction of bacteria
in a liquid nutrient medium is characterized by a change of phases or stages:
The reproduction of bacteria in a liquid nutrient medium is
characterized by a change of phases or stages
1.lag phase is the initial stage of bacteria adaptation to the nutrient medium. During this phase the synthesis of adaptive enzymes is observed. The lag phase is the period from the moment of importation (inoculation) of bacteria into the nutrient medium to their growth. During this phase the number of living bacteria does not increase, and may even decrease. The duration of this phase is from two till four hours;
2. log phase (exponential, logarithmic) is the phase of an intense increase of the bacteria number and an increase of the microbial cells number exponentially at the end of the first generation (first division), two cells are formed from one cell, at the end of the second – four cells, and so on. During this period the rate of cell reproduction and the increase of the bacterial population are maximum. The generation period is the period of time between two consecutive divisions of bacteria, which is permanent for this type of microorganisms. The duration of this phase is 5-6 hours;
3.stationary phase is the phase of maximum cell accumulation and development of balance between cell reproduction and death. The number of new bacteria is almost equal to the number of dead ones, that is, there is a balance between the dead cells and the newly formed cells. There is no increase in the number of microorganisms at this stage. The duration of this phase is 2 hours;
4.death phase is a decrease in the population due to a decrease in nutrients and changes in cultivation conditions (changes in pH, ion concentration, etc.). The duration of this phase is about 5 hours. The living cells that remain are in a state of rest.
Yeast budding
Nutrient media
In microbiology a nutrient medium is a medium containing various combinations
of complex or simple composition, which are used for the reproduction of
microorganisms in laboratory or industrial conditions. The needs of microorganisms for nutrients are diverse and are determined by the
peculiarities of their metabolism. The nutrient medium have to meet the following requirements:
the nutrient medium should include an energy source available to the cell (for phototrophs it is light, for chemoorganotrophs it is an organic or inorganic substrate).
2. the nutrient medium should have all the necessary components for biosynthetic processes
in the cell:
it have to contain nutrients in an easily digestible form; have optimal humidity, pH,
viscosity,
buffer capacity and, if possible, should be transparent.
2 Classification of nutrient media
The choice of a nutrient medium depends a lot on the purposes of the experiment, and the existing classification of nutrient media
takes into account the characteristics of their following features.
Media are divided into natural, semi-synthetic and synthetic with an indefinite and definite composition.
2.According to the role of the medium, it is divided into basal, elective and differential diagnostic.
3. According to the consistency
1. Natural media consist of products of plant or animal origin and have an indefinite chemical composition. Products of plant or animal origin are treated with enzymes (trypsin, pancreatin, papain), this leads to incomplete hydrolysis of proteins and the formation of peptones. As a rule, microorganisms grow better on peptone nutrient media than on nutrient media prepared from mixtures of amino acids. During enzymatic hydrolysis growth factors are probably preserved. For example: a mixture of proteins after hydrolysis of meat, fish, etc. Vegetable media: potato agar, tomato agar, corn extract, decoctions of cereals, yeast, beer wort, hay infusions, etc.
Semi-synthetic media of indefinite composition: Into semi-synthetic
media identified combinations (amino acids, vitamins, etc.) are imported
as necessary combinations, and a small amount of natural medium
is also added.
Synthetic media are media of a certain composition, represented by
pure chemical combinations taken in precisely specified concentrations and ratios of single elements. Obligatory components of such media are inorganic salts and carbon-and nitrogen-containing substances (for example:
glucose and ammonium sulfate-(NH4) 2SO4). These media are necessary for studying the physiology and metabolism of microorganisms, etc.
2.According to the role media are divided into basal, elective and differential diagnostic.
Basal media. They are used for growing many bacteria. For example, these are hydrolysates
of fish or meat (casein protein), from which a liquid medium (nutrient broth) and a
dense one (nutrient agar) are prepared. These include meat-peptone agar (MPA), which is used for the cultivation of mesophilic aerobic and facultative anaerobic
microorganisms, and malt agar (MA)-used for the cultivation of yeast and mold fungi.
Such media are a basis for the preparation of more complex nutrient media. Sometimes synthetic nutrient media are used as the basal ones, amino acids, vitamins, peptone, yeast extract, etc. are added to these media.
Elective media. The media contain substances that inhibit the growth of some bacteria,
but do not affect the growth of other bacteria.They are used for growing one or a whole physiological group of microorganisms.
Selective media contain not only substances that inhibit the growth of some types of bacteria, but also stimulators of the growth of other bacteria.
For example:
for the predominant growth of gram - negative bacteria - enterobacteria - triphenylmethane
dyes (crystalline purple, malachite green, etc.) are added to the nutrient medium.
2. to export staphylococci, sodium chloride is added to the medium at a concentration
of 7.5 % . At this level of concentration the growth of other bacteria
is suppressed. Yolk Salt Agar contains not only an elective factor
(sodium chloride), but also a differentiating agent (yolk). This allows you to determine the presence of the enzyme lecitovitellase in staphylococci.
Elective media are used at the first stage of export of a pure bacterial culture,
that is when obtaining a cumulative culture.
For example, Levin's medium contains eosin and methylene blue as indicators,
and is initially colored black and blue. Cells that carry out fermentation form colonies
that are colored black with a metallic luster, and colonies that do not have this property are colorless.
This medium allows to distinguish bacteria of the genus Escherichia from bacteria of the genus Proteus. For the same purpose the Endo media is often used in practice.
The Endo media Salmonella and Shigella
Levin's medium Salt Egg Yolk Agar Base
staphylococci
Differential diagnostic media. They are used in clinical bacteriology for fast identification and determination of species, as well as closely related species of microorganisms. The principle of constructing such media is based on the fact that different types of bacteria differ in their biochemical
activity and have an unequal set of enzymes that break down the substrates being included to the nutrient medium.
The composition of the differential diagnostic medium includes:
a) the main nutrient medium that ensures the reproduction of bacteria;
b) a certain chemical substrate, the relation to which is a diagnostic sign for this microorganism; c) a color indicator, its color change indicates a biochemical reaction and the presence of the enzyme system in
the studied microorganism.
Levine EMB Agar, Levin media
For example, Levin's medium contains eosin and methylene blue as indicators, and is initially colored black and blue. Cells that carry out fermentation form colonies
that are colored black with a metallic luster, and colonies that do not have this property
are colorless.This medium allows to distinguish bacteria of the genus Escherichia from bacteria
of the genus Proteus. For the same purpose the Endo media is often used in practice.
Escherichia Coli E.coli Cultured with Eosin Methylene Blue EMB Agar
Escherichia coli on EMB agar with metallic sheen
MacConkey agar: differential and selective medium
Escherichia coli on Endo agar
Ploskirev medium
Elective media
Differential diagnostic media. 3. According to the consistency media can be liquid,
semi-solid, solid, loose.
Liquid nutrient media is obtained by dissolving a certain necessary
set of nutrients, macro – and microelements in water.
According to the composition they can be both natural and synthetic.
Solid media in the form of dense gels have been used in
bacteriology since the time of Robert Koch. The main advantage of solid media is that it is possible to grow microorganisms on them in the form of colonies that are the offspring of a single cell.
To prepare solid nutrient media you need to add solidifying agents to liquid media. Agar, gelatin, silica gel, carragheenan are used as solidifying agents.
Semi-solid media contain a gel-forming substance in a low (0.3–0.7% zero point three, zero point seven percent) concentration and have a soft jelly-like consistency. Such media are suitable for studying the mobility and chemotaxis of cells, the cultivation of microaerophiles.
Loose media are a mass of more or less crushed and moistened raw materials (often
vegetable materials). Their main purpose is to be used in the food industry (obtaining soy sauce), agriculture (silage of feed, mushroom cultivation), etc. Determination of the nutrient medium composition assumes that such biophysical factors as the pH of the medium, temperature, supply and removal of molecular oxygen, which are critical for the growth of any bacterial culture, will also be taken into account.
Agar. The most common solidifying agent is agar - a polysaccharide exported from red seaweed and consisting of two polysaccharides – agarose (70 %) and agaropectin. It has
a number of useful properties, in particular:
1) it is able to form gels in water;
2) it melts at a temperature of 100 °C and hardens at 45 °C;
3) it is not broken down under the influence of enzymes of many types of microorganisms;
4) thermolabile substances and living microorganisms are not destroyed being added to molten agar heated to 45 °C, if the mixture is immediately cooled;
5) agar gels have a high degree of transparency;
6) the most commonly used concentrations of 1.5-2.0 % are relatively low and their use is relatively economical.
To prepare solid nutrient media you need to add solidifying agents to liquid media. Agar, gelatin, silica gel, carragheenan are used as solidifying agents.
Structural features of agar
Gelatin Hydrolysis Test
Silica gel
Carragheenan
Gelatin is a protein product of denaturation of collagen protein. Gelatin is obtained by boiling bones, cartilage and hooves of animals. The " solidifying " concentration of gelatin is 17-20 %. It is used for special purposes, because the gel formed by it melts at temperature of about 30 °C and solidifies at 23°C . In addition gelatin is liquefied by proteolytic enzymes of many microorganisms.
Silica gel is silicon dioxide (SiO2). Media based on silica gel (1.5-2.0 %) is used to obtain cultures of autotrophic bacteria, because there are no organic substances in the medium. With the help of silica gel media it is also possible to determine the needs of bacteria for vitamins.
Carragheenan ("vegetable gelatin" – is extracted from certain types of red seaweed.
Carrageenan is cheaper than agar, it is used in a concentration of 2 %, it is not destroyed by most types of bacteria. However, the prepared media should be poured at a high temperature – 55-60 °C.
Variety of media for the cultivation of microorganisms
A thermostat-shaker
Cultivation of microorganisms
Methods of cultivation of aerobic and anaerobic microorganisms
The cultivation of microorganisms, in addition to the
composition of the nutrient medium, strongly depends on physical and chemical factors (temperature, acidity, aeration, light, etc.). At the same time,
the quantitative indicators of each of them
are not the same and are determined by the peculiarities
of the metabolism of each group of bacteria.
Methods of cultivation of aerobic and anaerobic microorganisms
The cultivation of aerobic microorganisms
is carried out on the surface of dense media
or on a thin layer of liquid media, when
microorganisms receive oxygen directly from the air;
– in liquid media, during deep cultivation, microorganisms
use oxygen dissolved in the medium or constant aeration is
necessary for the growth of aerobic bacteria inside the medium.
The simplest and most widely used method of deep cultivation in laboratory is growing
in shakers that provide shaking of flasks or test tubes at a speed of 100-200 rpm or more.
While working it is convenient to use a thermostat-shaker (with a swinging platform). In addition to mixing, it is possible to aerate the culture of microorganisms by blowing under pressure through the sterile air medium.
Cultivation of anaerobic microorganisms.
1. Aerotolerant bacteria grow well on the surface of agar and cups at a low oxygen concentration.
2. Obligatory anaerobes.
Although bacteria are usually considered to be obligatory anaerobes, which
growth is impossible in the presence of dissolved oxygen,
in practice, anaerobic bacteria are those that do not grow on the surface
of a solid or semi-solid medium in air at atmospheric pressure.
To remove oxygen and create appropriate cultivation conditions, the
following methods are recommended:
Cultivation in an anaerobic jar, for example, anaerobic jar AЭ-01 is
a machine for growing microorganisms, where air is replaced by a gas
mixture. The most commonly used mixture has the following
composition: nitrogen with five percent of carbon dioxide CO2
and ten percent of hydrogen 10 % H2.
2. The use of chemicals that absorb molecular oxygen. In laboratory
practice an alkaline solution of pyrogallol, sodium dithionite (Na2S2O4),
metallic iron, monovalent copper chloride and some other reagents are used as absorbers of molecular oxygen. The absorbers are placed in a container (a flask, etc.) and tightly closed.
With this method of creating anaerobic conditions, it is necessary to take into account the absorption capacity of reagents and the volume of the enclosed space where bacteria are grown.
Anaerobic jar for the
cultivation of anaerobes
sodium dithionite pyrogallol
Anaerobic jar for the cultivation of anaerobes
BD GasPak
BD GasPa
3.The use of reducing agents that reduce the redox potential of the medium: cysteine, ascorbic acid, etc. The removal of oxygen from the medium as a result of fast heating
and boiling of the medium, followed by rapid cooling. If anaerobic microorganisms are
inoculated in such a media and a mixture (1:1 one to one) of oil and paraffin is layered, then in such conditions the growth of non-strict anaerobes will be observed.
4. It is possible to co-grow with aerobic or facultative anaerobic bacteria. In a liquid medium,
cultivation of E. coli is carried out, which leads to the removal of residual oxygen from the medium. Before inoculation of anaerobes, E. coli cells are killed by heating.
There is also a modification of the joint cultivation of microorganisms on a solid medium. On half of the Petri dish, some aerobic microorganism is inoculated, on the other – an anaerobe. The edges of the dish are filled with paraffin. The growth of the anaerobic microorganism will begin after the full use of oxygen by the aerobic organism.
to co-grow with aerobic or facultative anaerobic bacteria
5. Other methods of cultivation of anaerobic bacteria that restrict air access to the growing culture:
- growing on a high layer of medium; - growing on a dense medium;
- cultivation in viscous media, where the diffusion of molecular oxygen into the medium decreases with an increase in its density; - filling the medium with an inoculation with a high layer of sterile vaseline oil or paraffin;
- cultivation in a carbon dioxide (CO2) thermostat-incubator is the most
modern and effective method of working with anaerobic bacteria or using
an anaerobic workstation.
CO -incubators
An Anaerobic workstation
BD GasPak™ EZ Container Systems To differentiate pathogenic anaerobes such media are used as: - Zeissler blood agar (contains meat-peptone agar, glucose and blood);
-sugar meat-peptone agar;
the Willis-Hobbs medium contains, in addition to nutrient agar, lactose, an indicator, egg yolk and skimmed milk. Clostridia change the color of the indicator
to red (lactose fermentation) and form zones (halos) around the colonies (lecithinase activity).
Colonies of C. perfringens are colored in the color of the indicator and have a halo of opalescence;
iron-sulfite agar (Wilson-Blair medium) contains sodium sulphate and iron chloride, anaerobic bacteria form black colonies;
the Kitta-Tarozzi medium is a liquid medium consisting of a meat-peptone broth enriched
with animal liver products and contains pieces of boiled liver as a free oxygen absorber.
Zeissler blood agar
Kitta-Tarozzi medium
Willis Hobbs Agar
Wilson-Blair medium
Studying of the cultural characteristics of microorganisms Peculiarities of the growth of microorganisms on dense and liquid
nutrient media refer to cultural, or macromorphological properties.
Growth on dense nutrient media.
On the surface of dense nutrient media, microorganisms can
grow in the form of a colony, a stroke or a continuous lawn.
A colony is an isolated cluster of cells that are the offspring of a single cell.
Depending on where the cells were developing (on the surface
of a dense nutrient medium, inside it or at the bottom of the vessel), surface, subsurface and bottom colonies are distinguished. Colonies that have grown on the surface of a dense medium are very diverse.
When describing colonies, the following features are taken into account:
color, form, size, surface, light transmission,
colony profile, colony edge, structure, consistency,
degree of immersion in the medium, luminescence.
colony color – colorless (dirty-white colonies refer to a colorless one)
or pigmented – white, yellow, red, black, etc. The release of pigment into the air
and the substrate is also important.
– the shape of the colony: rounded, amoeboid, irregular, rhizoid, etc.;
– the size (diameter) of the colony is measured in millimeters. If the size of the colony does not
exceed 1 millimeter, then they are called pointed colonies;
the surface of the colony is smooth, rough, furrowed, folded, wrinkled, with concentric
circles or radially striated;
– Colony profile: 1-curved; 2-crater-shaped; 3-bumpy; 4-growing into the substrate;
5-flat; 6-convex; 7-teardrop-shaped; 8-cone-shaped
Variety of colonies of microorganisms
Variety of colonies of microorganisms
Variety of colonies of microorganisms
The shape of the colonies : round (a), round with a scalloped edge (б), round with a roller along the edge (в), rhizoid (г,д), with a rhizoid edge (е), amoeba (ж), filamentous (з), folded (и), irregular (k), concentric (л), complex (м). Colony profile
The shape of the colony edge: 1-smooth (S-shape),
2-wavy, 3-scalloped, 4-lobed, 5-irregular, 6-ciliated,
7-filamentous, 8-villous, 9-branched
– gloss and transparency of the colony - shiny, dull, powdery, transparent;
– the shape of the colony edge – smooth, wavy, scalloped, fringed, etc.;
– the structure of the colony – homogeneous, close and coarse-grained,
wavy, etc.; the shape of the edge and the structure of
the colony is determined with a magnifying glass or under low magnification of a microscope. To do this, the cup is placed on the table with the lid up.
the consistency of the colony is determined by touching its surface with a loop. The colony can be easily removed from the agar, be dense, soft or growing into the agar,
slimy (sticks to the loop), viscous, it can have a veil which is removed entirely, brittle (easily breaks when touched by the loop).
S, R, M and D colonies
Colonies of the same species growing from a pure culture can be smooth (S) and rough (R). There are 4 types of colonies.
1.Smooth, or S-colonies are convex, shiny, have smooth edges, smooth surface. S-forms of microorganisms are more virulent (pathogenic). This type of colonies
has hydrophilic polysaccharides in the outer shell of microorganisms. When growing
in the broth, they are turbid; they are biochemically active. They are released more often during the acute period of the disease.
2. Rough, or R-colonies - flat, turbid, have an uneven edge and a rough (striated) surface.
The R-forms of microorganisms are often avirulent. This type of colonies is associated with
the hydrophobicity of the outer shells of bacteria. They grow in broth in the form of sediment.
Biochemical properties are poorly intensed; most bacteria are less pathogenic; they are usually released during the chronic form of the disease.
More often pathogenic bacteria have the S-form. The exceptions are the causative agents of tuberculosis - mycobacteria, plague - yersinia pestis, anthrax - bacilli, in which the R-form is pathogenic.
3.Mucous, or mucoid M-colonies are found in klebsiella, they have an intense
polysaccharide microcapsule.
4. D colonies - dwarf colonies
Phenazine production modulates colony morphology in P. aeruginosa PA14.
Classification of bacteria according to sensitivity to pH, temperature, salts
The intensity of the growth of microorganisms is influenced by physical and chemical factors.
According to the sensitivity of bacteria to pH, they are divided into:
Alkalophilic bacteria (late latin alkali, alcali, from Arabic. alqali -vegetable ash + Greek. philos loving) reproduce themselves well in an alkaline media at pH 8.0 ; alkalophiles include, for example, cholera vibrions.
Acidophilic bacteria – reproduce themselves well in an acidic
media at pH from 3.0 till 4.0 ; acidophiles include, for example, lactic acid bacteria.
Cholera vibrions
Lactic acid bacteria
2. According to the sensitivity to temperature, there are:
Psychrophilic bacteria (synonym - psychrophiles) — their temperature optimum of growth is in the range from eight degrees Celsius below the zero to ten degrees Celsius above the zero.
Mesophilic bacteria (synonym- mesophiles) — their the temperature optimum of growth is in the range from +20° - +40°; most pathogenic bacteria belong to mesophiles.
Thermophilic bacteria (synonym - thermophiles) — the temperature optimum of growth is in the range from 50-75° above the zero.
Psychrophilic bacteria Thermophilic bacteria 3. According to the sensitivity of bacteria to salts, they are:
Halophilic microorganisms (from Greek. hals - salt and phileo - love) are bacteria, yeast or mold fungi capable of growing in the presence of high concentrations of sodium chloride (NaCI). Halophiles are divided into :
Slight halophiles is up to 5%
Moderate halophiles is up to 15-16% Exremal gallophiles is above 16 %
Halophilic microorganisms are resistant to high osmotic pressure and to the specific action of sodium chloride NaCI. Some halophilic microorganisms can be developed in liquid nutrient media containing 25% of sodium chloride NaCI and do not grow in its absence. Halophilic microorganisms live in oceans, seas, salt lakes, salt marshes, etc. Many types of halophilic microorganisms form orange or red pigments (carotenoids). The development of such halophilic microorganisms on salted fish or salted animal skins is accompanied by the appearance of red spots.
Halotolerant microorganisms do not die from salt but do not need it, for example, Staphylococcus aureus.