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Bacteria nutrition, metabolism
and growth.
Dr. Edet E. Udo PhD
Department of MicrobiologyFaculty of Medicine, Kuwait University.
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1. Gram- positive bacteria contain a thick layer of peptidoglycan (T/F)
2. The periplasmic space is present in both Gram-positive and Gram-negative bacteria ( T/F)
3. Bacterial LPS has both antigenic and virulent properties (T/F)
4. Staphylococcus is Gram-positive cocci in clusters (T/F)
5. A bacterial spore germinates into two daughter cells ( T/ F).
Match the following
1. Gram- positive cell wall contains____________ 2. Gram positive cocci in chains __________________
3. Has no cell wall ________________
4. A primary pathogen __________________________
5. An opportunistic pathogen _________________________
E.coli, Klebsiella spp, Streptococcus, Haemophilus influenzae,Teichoic acid, Vibro cholerae, Mycoplasma,
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Bacteria nutrition, metabolism and growth.
Objectives Define nutrition, explain the nutritional
requirements of bacteria.
Define bacterial growth.
Discuss the phases of microbial growth andtheir relationship to generation time
Define metabolism and the fundamental
differences between anabolism and catabolism Describe cultivation of bacteria in the
laboratory
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Bacterial nutrition
Definition: Nutrition
Nutrition is a process by which organisms acquire
chemical substances (Nutrients) used in cellularactivities 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 cellsize and number of cells in a population
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Metabolismincludes 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, carbohydrates Micronutrients or trace elements: required
in smaller amounts.
E.g. zinc, manganese.
Are involved in enzyme functions andmaintenance of protein structure.
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Bacterial growth
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.
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Cell division
Generation or doubling time:The average generation time forbacteria is 30-60 minutes underoptimum conditions.
Most pathogens such as Staphylococcusaureus and Escherichiacoli double in 20 30 minutes.
The longest generation time requiresdays. E.g. Mycobacterium leprae thatcauses leprosy doubles in 20 to 30days.
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Planes of division
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The growth curve
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The growth curve The growth curve is a graphic representation of
closed population of bacteria overtime This occurs in four phases, lag, log, stationary and
decline phases.
1.The lag phase, Cells adjust to new environment. There is no change in the number of cells but
metabolic activity is high leading to increase incellular components.
2. The log or exponential phase, Bacteria multiply at the fastest rate possible under
the conditions provided. Are susceptible to cell wall active antibiotics Form metabolic end products
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3. The stationary phase
there is an equilibrium between cell divisionand cell death caused by : decrease in nutrient,
increase in cell population and accumulation of
metabolic waste / end products e.g antibiotics. Sporulating cells initiate spore formation
4. Death or Decline phase
The number of death cells exceeds the number
of new cells formed due to lack of nutrientsand accumulation of toxic waste
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Factors affecting bacterial
growth Nutritional requirements Chemical: water, carbon source, nitrogen, minerals, oxygen,growth factors
Carbon Source: All bacteria require carbon for growth.
Bacteria can been classified on the basis of theircarbon source. Autotrophs: use carbon dioxide as the sole
source of carbon Heterotrophs: use more complex organic
compounds such as carbohydrates and aminoacids as source of carbon Photoautotroph- energy need is supplied by
light Chemoautotroph - energy is extracted from
inorganic substances
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Inorganic nutrients (ions):
Contain no carbon and hydrogen atoms :
phosphates, potassium, magnesium, nitrogen,sulfur, iron and numerous trace metals.
Organic nutrients:
contain carbon and hydrogen atoms. Includecarbohydrates, lipids amino acids, Nucleic acids etc.
Carbohydrates:
are used as the initial carbon source for manybiosynthetic 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.
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Nutritional factors Phosphorus is present as phosphates salts.
They function in energy metabolism and asconstituents of nucleic acids, phospholipids,
teichoic acids, ATP, etc Minerals:
K, Mg, Ca, Fe are required in relatively highlevels.
Function as cofactors in enzyme reactions and ascations they act as buffers within the cells
Vitamins,
purines and pyrimidines ( accessory growth
factors) function as coenzymes
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Physical factors
Oxygen requirement:
Bacteria can be divided into five groups on thebasis of their oxygen requirements
1. Obligate or strict aerobes:
The growth of bacteria is inhibited by absenceof oxygen An example of a strict or obligateaerobe is Pseudomonas aeruginosa
2. Obligate anaerobes:
Growth is inhibited by the presence of oxygen. Examples of obligate anaerobe are Clostridium spp
and Bacteriodes spp.
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3. Facultative anaerobes are able to grow in the presence or absence
of molecular oxygen. E.g. includestaphylococci, streptococci, Enteococci, etc. 4. Microaerophilic bacteria: grow best under increased carbon dioxide
tension. Examples include Neisseria
gonorrhoeae, Haemophilus influenzae 5.Aerotolerant bacteria: can survive (but not grow) for a short period
of time in the presence of atmosphericoxygen
Tolerance to oxygen is related to the abilityof the bacterium to detoxify superoxide andhydrogen peroxide produced as bye productsof aerobic respiration.
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1. Superoxide dismutase,
which converts superoxide ( a toxic metabolite)
into hydrogen peroxide is present in aerobic andaerotolerant bacteria but not in obligate anaerobes.
2. Catalase,
which converts hydrogen peroxide into water and
oxygen is also present in all aerobic bacteria but islacking in aerotolerant organisms. Strict anaerobeslack both enzymes.
O2
- + O2
- -superoxide dismutase H2
O2
(Hydrogen
peroxide) + O2-
H2O2 + H2O2 Catalase-------2H2O +O2
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Temperature: There are three critical temperature ranges for
growth:
(a) Minimum temperature- (b). Maximum temperature: . Optimum temperature: Psychrophiles: Has optimum temperature below 15 C but
capable of growth at 0 C Mesophiles:
grow at a range of 20 40 C. Include mostbacterial pathogens with optimum temp. at 37C
Thermophiles: microbes that has optimum temperature above
45 C with a general range of 45-80 C Most thermophiles form spores e.g. Bacillus
steareothermophilus
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pH:
Optimum pH for most bacteria is near pH 7.0(pH 6.5- pH 7.5)
Bacteria can be classified as alkalinophiles,neutrophiles or acidophiles according to theirdegree of tolerance to pH changes
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Osmotic pressure:
When a microbial cell is in ahypertonic solution cellular watermoves out of the cell through the cellmembrane to the hypertonic solution.
This osmotic loss of water causesshrinkage of the cell PLASMOLYSIS
In a hypotonic solution such as indistilled water, water will enter thecell and the cell may be lysed by suchtreatment (PLASMOPTYSIS).
Halophiles
require high salt concentrations for
growth. Some bacteria can tolerate15% salt. E.g. S. aureus
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Bacterial metabolism
Metabolism consists of catabolic and anabolicreactions.
Anabolic reactions are energy-requiring subset ofmetabolic reactions, which synthesize largemolecules from smaller ones.
Catabolic reactions are the energy releasingsubset of metabolic reactions, which degrade orbreakdown large molecules into smaller ones.
Metabolism is best considered in three stages
1. Energy metabolism 2. Respiratory metabolism
3. Biosynthetic pathways
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1. Energy metabolism
Energy used by bacteria is primarily produced by
fermentative and/ or respiratory metabolic pathways. Metabolic reactions are catalyzed by enzymes
Anaerobic metabolism (fermentative metabolism
A. Glycolytic ( Embden-Meyerhof ) pathway
The major glucose utilization pathway.
Glycolysis- the metabolism of glucose to yield pyruvicacid and 2 ATP molecules
B. Entner-Doudoroff pathway
Aerobic metabolism ( respiration)
The Krebs cycle
Involves the the metabolism of 2-carbon groups to carbondioxide and water and the production of ATP.
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Biosynthetic pathways Used to build small molecules with nitrogen,
sulphur and other minerals into aminoacids, purines, pyrimidines, polysaccharidesand lipids
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Bacterial metabolism
Uses of energy
For biosynthetic activities e.g. cell wall synthesis,protein synthesis, nucleic acid synthesis etc
Membrane transport and movement e.g active
transportation. Uses of metabolic products in the laboratory
Metabolic end products e.g. pyruvic acid, lactic acid,mixed gases, alcohols, are used for bacterialidentification. (Biochemical tests) e.g. oxidase tests,
catalase tests.
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Cultivation of bacteria in the
laboratory Culture media: Any material prepared for the
growth of bacteria in thelaboratory.
They can be broth (liquid) or solid media ( contains a gelling
substance such as agar)
Microbes that grow on a culturemedium are known as a culture.
When grown on solid media, thegrowth is calledcolony .
Growth in a liquid medium isdemonstrated by turbidity.
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Types of Culture media:
Defined synthetic medium: contains known quantities of specific nutrients
contain nutrients of reasonably well-
Complex medium:
known composition that varies from batch tobatch
Enrichment medium: (liquid medium)
is used to encourage the growth of aparticular organism in a mixed culture
Enriched media: (Solid medium,)
contain additional nutrients to support thegrowth of fastidious organisms. E.g bloodagar and chocolate agar
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Chocolate agar contains lysed blood.
The lysis releases intracellular nutrients such as haemin (X factor) and
the coenzyme nicotinamide adenine dinucleotide (NAD or V factor)into the agar for use by fastidious microorganisms such as
Haemophilus species andNeisseria gonorrhoeae.
Selective media:
contains salts, dyes or other chemicals that inhibit the growth
unwanted microorganisms.
Differential media:
contain chemicals that allow the distinction between different types of
organisms e.g. Lactose in MacConkey agar.
Preservation of bacterial cultures:
By refrigeration,, lyophilization, storage in liquid nitrogen
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Culture media