Download Bacterial nutrition and growth

Bacterial nutrition and growth
Importance of Microorganisms
Assistant Prof. Dr. Karreema Amine AL-Khafajii ,Babylon University, College of
Medicine, Department of Microbiology.
Definition: Nutrition:
Nutrition is a process by which organisms acquire chemical substances(nutrients), used in
cellular activities such as metabolism and growth. Organisms differ in the use of particular
elements, their source, and chemical form.
Microbial growth
Microbial growth refers to both the increase in cell size and number of cells in a
population.
Metabolism :includes all the biochemical reactions that occur in the cell.
It consists of anabolic and catabolic reactions.
Categories of essential nutrients: Macronutrients: required in relatively large
quantities.e.g. proteins and carbohydrates.
Micronutrients or trace elements: required in small amounts .e.g. zinc and manganese.
They are important because they are involved in enzyme functions and maintains of
protein structure.
Bacteria growth
Bacteria growth by cell division; binary or transverse division. During binary fission the
parent cell enlarges, duplicates its chromosomes and forms a central transverse septum that
divides the cell into two daughter cells.
Generation or doubling time: the average generation time for bacteria is 30-60 minutes
under optimum condition. Most pathogens such as Staphylococcus aureus and E. Coli
double in 20-30 minutes. The largest generation time requires days. E.g.Mycobacterium
leprae that causes leprosy doubles in 20-30 days.
The growth curve
The growth curve is a graphic representation of closed population of bacteria overtime.
This occur in four phases; lag, log (exponential), stationary, and decline phases.
1- the lag phase: in which cells adjust to new environment. There Is no change in the
number of cells, but metabolic activity is high leading to increase in cellular components.
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2-the log or exponential phase: bacteria multiple at the fastest rate possible under the
conditions provided. Bacteria here are(1) susceptible to cell wall active antibiotics.(2)form
metabolic end product.
3-the stationary phase: there is an equilibrium between cell division and cell death caused
by: (1)decrease in nutrient. (2) increase in cell populations. (3)accumulation of metabolic
waste/ end products, e.g. antibiotics.
*sporulating cells initiate spore formation.
4-Death or decline phase: the number of death cells formed due to lack of nutrients and
accumulation of toxic waste. In clinical conditions such as abscess, the bacteria inside
reached the stationary phase of the growth curve; cant take nutrient or other substances like
antibiotics from the surrounding as the abscess is separated by wall from the surroundings.
So if we give antibiotic to the patient in this stage is of no benefit, so in order to resolve
this problem we should open the abscess surgically to get out the waste product that inhibit
the growth of bacteria and also the fresh nutrient will enter from the surroundings that help
bacteria to multiply again, and so antibiotic if given here to the patient it will be effective.
Growth of bacteria in an open environment, such as; soil, water. Or even the intestine,
generally dose not follow the growth curve shown above, in these circumstances bacterial
growth is most often continuous, so that the number of viable microorganisms fairly
continuous over long period of time. This thought is used in the laboratory to grow the
bacteria in a continuous media to get the growth exponentially in a condition of a balance
growth, and that the generation time is determined by the rate at which fresh nutrients and
other needed important factors for the growth are supplied to the culture continuously.
Continuous culture is used by genetic engineering for synthesis of important wanted things
like; insulin, vitamins, enzymes..etc. The human normal flora that live on the skin, mouth,
intestine and vagina are grow continuously be add , while balanced microbial growth may
occur to some extent in chronic disease conditions.
Factors affecting bacterial growth:
1- Nutritional requirements: *chemical; water, carbon source, nitrogen, minerals,
oxygen, growth factors.
*carbon source:
*all bacteria require carbon for growth. bacteria can be classified on the bases of their
carbon source: -Autotrophs: use carbon dioxide as the sole source of carbon.
-Hetrotrophs: use more complex organic compounds, such as ; carbohydrates and amino
acids as source of carbon.
-photoautotroph-energy need is supplied by light.
-chemoautotroph- energy is extracted from inorganic substances.
*Inorganic nutrients(ions): contains no carbon and hydrogen atoms. phosphate.
potassium, magnesium, nitrogen, sulfer, iron. And numerous trace metals.
*organic nutrient: contain carbon and hydrogen atoms, include ;carbohydrate, lipids,
amino acids, nucleic acids…etc.
*Carbohydrate : are used as the initial carbon source form any biosynthetic pathways and
as electron donors(energy source)by many bacteria.
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*Amino acids are important source of carbon and nitrogen. The nitrogen is converted to
ammonia.
*Phosphorous is present as phosphate salts. They function in energy metabolism and as
constituents of nucleic acids, phospholipids, teichoic acids,ATP.etc
*Minerals; K,Mg, Ca,Fe, are required in relatively high levels. Function as cations, they
act as buffers with in the cells.
*Vitamins; purines and pyrimidines (accessory growth factors) function as Coenzymes.
Physical factors
*Oxygen requirement: bacteria can be divided into five groups on the basis of oxygen
requirements; 1- Obligate or strict aerobes:
In which the growth of bacteria is inhibited by absence of oxygen.e.g.Pseudomonues
aerogenosa.
2-Obligate anaerobes: growth is inhibited by the presence of oxygen.e.g.Closteridium
spp. And Bacteroides spp..
3- Facultative anaerobes: are able to grow in the presence or absence of molecular
oxygen,e.g.Staphylococcus and Streptococcus.
4-Microaerophilic bacteria: are grow best under increased carbon dioxide
tension.e.g.Neisseria gonorrhea.
5-Aerotolerent bacteria: can survive (but not grow) for a short period of time in the
presence of atmospheric oxygen. Tolerance to oxygen is related to the ability of the
bacteria to detoxify superoxide and hydrogen peroxide produced as bye roducts of aerobic
bacteria.
1-Superoxide dismutase: which converts superoxide (a toxic metabolite) into hydrogen
peroxide, which is present in aerobic and aerotolerent bacteria, but not in obligate
anaerobes.
2-Catalase: which converts hydrogen peroxides into water and oxygen. It is also present in
all aerobic bacteria. But is lacking in aerotolerent organism. Strict anaerobes lack both
enzymes.
Temperature: there are three critical temperature ranges for growth:
a) Minimum temperature.
b)Maximum temperature.
C) Optimum temperature.
Psychrophiles: has optimum temperature below 15 C but capable of grow at 0 C.
Mesophiles: grow at a range of 20-40 C, this type includes most pathogenic bacteria, with
optimum temperature 37 C.
Thermophiles: microbes that has optimum temperature above 45 C, with a general range
of 45-48 C. most thermophiles form spores.
PH: optimum PH for bacteria is near PH 7.0 (PH6.5- PH 7.5).. bacteria can be classified as
a alkalinophiles, neutrophiles or acidophiles according to their degree of tolerance to PH
changes.
Osmotic pressure: when a microbial cell is in a hypertonic solution ,cellular water moves
out of the cell through the cell membrane to the hypertonic solution. This osmotic loss of
water causes shrinkage of the cell (plasmolysis).
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While in a hypotonic solution, such as in ditalled water, water will enter the cell and the
cell may be lysed by such treatment (plasmoptysis).
Halophiles: require high salt concentration for growth, some bacteria can tolerate 15%
salt.e.g. Staphylococcus aureus.
Bacteria metabolism
Metabolism consists of catabolic and anabolic reactions.
-Anabolic reactions: are energy-requiring subset of metabolic reactions, which synthesize
large molecules from smaller ones.
-Catabolic reactions: are the energy-releasing subset of metabolic reactions, which
degrade or break down large molecules into smaller ones.
Metabolism is best considered in three stages:
1-Energy metabolism
2-Respratory metabolism
3-Biosynthetic metabolism.
1-Energy metabolism is used by bacteria is primarily produced by fermentation and / or
respiratory metabolic pathway. Metabolic reactions are catalyzed by enzymes.
Anaerobic metabolism(fermentative metabolism):
A glycolytic (Embden-Meyerhof) pathway, the major glucose utilization pathway.
Glycolysis (a) is the metabolism of glucose to yield pyruvic acid and 2 ATP molecules in
the absence of oxygen, this process is commonly occur in yeast. These pyruvic acid
molecules then be utilized for ATP production through the reactions of the Kreps cycle and
electron transport to yield 36 ATP, or they may be utilized in fermentation process.
(b) enter Doudoroff pathway.
Aerobic metabolism (respiration): The kreps cycle involves the metabolism of 2-carbon
groups to carbon dioxide and water and the production of ATP.
Biosynthetic pathway: used to build small molecules with nitrogen, sulfer, and other
minerals into amino acids, purins, pyrimidins, polysaccharides and lipids.
Uses of energy:(1) for biosynthetic activities e.g. cell wall synthesis, protein synthesis,
nucleic acid synthesis…etc.
(2) membrane transport and membrane movement.e.g. active transport.
Uses of metabolic transport in the laboratory:
Metabolic end products e.g. pyruvic acid, lactic acid, mixed gases, and alcohols are used
for bacterial identification (biochemical tests), e.g.oxidase test and catalase test .
Laboratory
Culture media: is any material prepared for the growth of bacteria in the laboratory. They
can be in the form of ; broth(liquid), or solid media (contains a gelling substance such as
agar. Microbes that grow on a culture medium are known as a culture. When grow on
solid media, the growth is called colony. Growth in a liquid medium is demonstrated by
turbidity.
Define synthetic medium: contains known quantities of a specific nutrients. Contain
nutrients of reasonably well-complex medium: known composition that varies from batch
to bach.
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Enriched media(liquid media):is used to encourage the growth of a particular organism
in a mixed culture.
Enriched media( solid media): contains additional nutrients to support the growth of
fastidious organisms.e.g. blood agar, and chocolate agar. Chocolate agar contains lysed
blood. The lysis releases intracellular nutrients such as haemin (x-factor), and the
coenzyme nicotinamide adenine dinucleoide (NAD, and V-factor) into the agar for use by
fastidious microorganisms, such as Haemophilus spp. And Neisseria gonorrheae.
Selected media: contains salt, dyes, or other chemicals that inhibited the growth of
microorganisms.
Differential media: contains chemical that allow the distinction between different types of
organisms.e.g. lactose in MacConkey agar.
Preservation of bacterial cultures:
By refrigeration, lyophilization, and storage in liquid nitrogen.
Importance of Microorganisms:
Microorganisms are vital to humans and the environment, as they participate in the
Earth's element cycles such as the carbon cycle and nitrogen cycle, as well as fulfilling
other vital roles in virtually all ecosystems, such as recycling other organisms' dead
remains and waste products through decomposition. Microorganisms also have an
important place in most higher-order multicellular organisms as symbionts. Many
blame the failure of Biosphere 2 on an improper balance of microorganisms. *Use in
digestion: Some forms of bacteria that live in animals' stomachs help in their
digestion. For example, cows have a variety of different microbes in their stomachs
that aid them in their digestion of grass and hay. *Use in food preparing (depending
on Fermentation) in ; brewing, wine making, baking, pickling and other food-making
processes.*They are also used to control the fermentation process in the production of
cultured dairy products such as yogurt and cheese. The cultures also provide flavour
and aroma, and inhibit undesirable organisms. *Use in water treatment ( Sewage
treatment), The majority of all oxidative sewage treatment processes rely on a large
range of microorganisms to oxidise organic constituents which are not amenable to
sedimentation or flotation. Anaerobic microorganisms are also used to reduce sludge
solids producing methane gas (amongst other gases) and a sterile mineralised residue.
In potable water treatment, one method, the slow sand filter, employs a complex
gelatinous layer composed of a wide range of microorganisms to remove both
dissolved and particulate material from raw water. *Use in energy :Microbes are used
in fermentation to produce ethanol, and in biogas reactors to produce methane.
Scientists are researching the use of algae to produce liquid fuels, and bacteria to
convert various forms of agricultural and urban waste into usable fuels. *Use in
production of chemicals, enzymes etc .Many microbes are used for commercial and
industrial production of chemicals, enzymes and other bioactive molecules.
Examples of organic acid produced include
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Acetic acid: Produced by the bacterium Acetobacter aceti and other acetic acid
bacteria (AAB)
Butyric acid (butanoic acid): Produced by the bacterium Clostridium butyricum
Lactic acid: Lactobacillus and others commonly called as lactic acid bacteria
(LAB)
Citric acid: Produced by the fungus Aspergillus niger
*Microbes are used for preparation of bioactive molecules and enzymes.
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Streptokinase produced by the bacterium Streptococcus and modified by
genetic engineering is used as a clot buster for removing clots from the blood
vessels of patients who have undergone myocardial infarctions leading to heart
attack.
Cyclosporin A is a bioactive molecule used as an immunosuppressive agent in
organ transplantation
Statins produced by the yeast Monascus purpureus are commercialised as
blood cholesterol lowering agents which act by competitively inhibiting the
enzyme responsible for synthesis of cholesterol. *Use in science :Microbes are
also essential tools in biotechnology, biochemistry, genetics, and molecular
biology. The yeasts (Saccharomyces cerevisiae) and fission yeast
(Schizosaccharomyces pombe) are important model organisms in science, since
they are simple eukaryotes that can be grown rapidly in large numbers and are
easily manipulated. They are particularly valuable in genetics, genomics and
proteomics. Microbes can be harnessed for uses such as creating steroids and
treating skin diseases. Scientists are also considering using microbes for living
fuel cells, and as a solution for pollution.
*Use in warfare (Biological warfare):In the Middle Ages, diseased corpses
were thrown into castles during sieges using catapults or other siege engines.
Individuals near the corpses were exposed to the deadly pathogen and were
likely to spread that pathogen to others. *Importance in human health (Human
digestion ): Microorganisms (Human flora) can form an endosymbiotic
relationship with other, larger organisms. For example, the bacteria that live
within the human digestive system contribute to gut immunity, synthesis
vitamins such as folic acid and biotin, and ferment complex indigestible
carbohydrates.
Diseases caused by microbes : as bacteria is beneficial to human and animals…. ,
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