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

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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.

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.

*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).

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.

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

• 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.

• 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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