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Microbial Nutrition and Growth (Nutrients (Essential Nutrient (Growth…
Microbial Nutrition and Growth
Microbial growth
involves an increase in the number of cells rather than in the size of individual cells
binary fission
simple and rapid
steps
1.parent cell enlarges
2.Chromosome duplicates and move to opposite sides
Protein band forms in center of cell
Septum forms
5.cell wall eventually forms a complete central septum
Growth of industrial and biotech organisms
Vitamin D by Saccharomyces
Vitamin B12 by Streptomyces
Vitamin C produced by Gluconobacter
Control of microbial growth is important for
Infection control
antimicrobials
antibacterial,
antifungal
Nutrients
a process by which chemical substances (nutrients) are acquired from the environment and used in cellular activities
requires elements (Carbon, Hydrogen, Oxygen)
Macronutrients- Elements required in large amounts
Essential Nutrient
any substances that must be provided to an organism
Growth factor
An organic compound such as an amino acid, nitrogenous base, or vitamin that cannot be synthesized by an organism and must be provided as a nutrient
many cells cannot synthesize all 20 amino acids so they must obtain them from food
The more growth factors required, the more fastidious the organism
Difficult to grow, complex nutritional requirement
Haemophilus influenza
Micronutrients - Elements required in trace amounts
Nutrients are processed and transformed into the chemicals of the cell after absorption
Nutritional categories
Based on carbon content
Organic nutrients
Contain carbon and hydrogen, usually the products of living things
Carbon is the backbone of all organic components present in a cell
H and O are also important as they are found in organic molecules
Heterotroph
an organism that must obtain its carbon in an organic form (nutritionally dependent on other living things).
Can be photo or chemo troph
Chemotroph
microbes that gain energy from chemical compounds
process these molecules through respiration or fermentation
types
Saprobes
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Parasites
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Phototroph: microbes that photosynthesize for energy = sunlight as energy source
Can not make their own energy
Inorganic nutrients
A combination of atoms other than carbon and hydrogen
Autotroph
an organism that uses inorganic CO2 as its carbon source.
Can be photo or chemo troph
has the capacity to convert CO2 into organic compounds
Not dependent on other living things- FREE LIVING
Can make their own energy
May use light or chemical as their energy source
Based on Energy sources
Energy is required for the biosynthesis of macromolecules, such as proteins
generation time
the time required for a complete fission cycle, from parent cell to two daughter cells
as long as the environment remains favorable, the doubling effect can continue at a constant rate
The length of the generation time- a measure of the growth rate of an organism
average generation time is 30 – 60 minutes
shortest generation times can be 10 minutes
This growth pattern is termed exponential
Stages in the Normal Growth Curve
Exponential growth (logarithmic or log) phase
Cells reach the maximum rate of cell division
will continue as long as cells have adequate nutrients and the environment is favorable
growth increases geometrically
Microbes in this phase of growth are more vulnerable to conditions that disrupt cell metabolism and binary fission
Stationary growth phase
caused by depleted nutrients and oxygen
cell division rate is slowing down
cell birth and cell death rates are equal
Caused by excretion of waste products (organic acids and biochemical pollutants) into the growth medium
lag phase
cells are not yet multiplying at their maximum rate
population of cells is so sparse or dilute that sampling misses them
newly inoculated cells requiring a period of adjustment, enlargement, and synthesis
Length of lag period varies from one population to another
Death phase
cells begin to die at an exponential rate due to the buildup of wastes
speed with which death occurs depends on the resistance of the species and how toxic the conditions are
Analyzing population size without culturing
Turbidity/turbidometry
Can be measured by a turbidimeter
This method of analysis cannot distinguish live from dead
the greater the turbidity, the larger the population size
Low turbidity
% of light transmitted is high
low growth
a clear nutrient solution becomes turbid or cloudy as microbes grow in it
High turbidity
% of light transmitted is low
high growth
Counting
Coulter counter
electronically scans a fluid as it passes through a tiny pipette
flow cytometer
measure cell size and differentiate between live and dead cells
direct cell count
measured microscopically
Viable Count
dilute sample and plate; detects only live cells
Steps
Plate dilutions of a bacterial sample
Incubate to allow cells deposited on the agar to grow into colonies
3.Count the plate with between 20 and 200 colonies
4.Multiply by dilution counts on live (viable) bacteria
Automated counting
coulter counter
electronically scans a culture as it passes through a tiny pipette
Cannot tell live from dead
Flow cytometer also measures cell size
The Population Growth Curve
Steps
Sampling the broth at regular intervals during incubation
Plating each sample onto solid media
Incubate this culture over a period of several hours
Counting the number of colonies present after incubation
Place a tiny number of cells in a sterile liquid medium
One colony on the plate represents one cell or colony forming unit (CFU) from the original sample
environmental conditions
temperature
Lower temperatures slow down biochemical reaction, reduce energy, and growth while high temperatures denature and inactivate enzymes
Psychrophiles
grow between -20o to 15oC
grow slowly in cold but have an optimum temperature above 20°C
True psychrophiles have optimum below 15oC
Pseudomonas
Less extreme Psychrotrophs have optimum between 15o and 30oC
Staphylococcus aureus and Listeria monocytogenes grow in refrigerated
Mesophile
An organism that grows at intermediate temperatures
Optimum growth temperature of most: 20°C to 40°C
Most human pathogens have optima between 30°C and 40°C
Group includes thermoduric microbes
Survive short exposure to high temperatures
Contaminants of heated or pasteurized products
Giardia, Bacillus and Clostridium
Thermophile
Vary in heat requirements
General range of growth of 45°C to 80°C
Fecal organisms
Isolation of strict thermophiles requires autoclave
A microbe that grows optimally at temperatures greater than 45°C
pH and salt
pH is the degree of acidity or alkalinity (basicity) of a solution
Majority of organisms live or grow in habitats between pH 6 and 8
A few organisms live in pH extremes
Obligate acidophiles
Like lower pH – acidic conditions
examples
Lactobacillus
Helicobacter
Molds and yeasts tolerate low pH and are most common spoilage agent of pickled foods!
Alkalinophiles
Hot pools and soils with high levels of basic minerals
Examples include urine decomposing bacteria
osmotic pressure
Transport Mechanisms
Transport of necessary nutrients occurs across the cell membrane, even in organisms with cell walls
The driving force of transport is atomic and molecular movement and uses the diffusion process
Diffusion
When atoms or molecules move in a gradient from an area of higher density or concentration to an area of lower density or concentration
Evenly distributes the molecules
determined by the concentration gradient and permeability of the substance
Simple or passive diffusion is limited to small nonpolar molecules or lipid soluble molecules
No energy (ATP) required
Other nutrients move by facilitated diffusion, active transport
Osmosis
the net passage of water through a selectively permeable membrane driven by a difference in solute concentrations on the two sides of the membrane
A selectively permeable membrane is one that allows unrestricted passage of water, but block certain other dissolved molecules
this process will continue until the concentration of water is equalized on both sides of the membrane
water flows from the solution with the lower solute concentration into the solution with higher solute concentration
Osmotic Relationships
determined by the relative concentrations of the solutions on either side of the cell membrane
Hypotonic
Net direction of osmosis is from the hypotonic solution into the cell
Cells without cell walls swell and can burst
The solute concentration of the external environment is lower than that of the cell’s internal environment
A slightly hypotonic environment can be favorable to bacteria cells
Isotonic
No net change in cell volume
Generally the most stable environment for cells
The environment is equal in solute concentration to the cell’s internal environment (0.85% Aqueous Solution)
Hypertonic
Will force water to diffuse out of a cell
high osmotic pressure
The environment has a higher solute concentration than the cytoplasm
hypertonic solutions such as concentrated salt and sugar solutions act as preservatives for food
Adaptations to Osmotic Variations
In fresh pond water- hypotonic conditions
Amoeba
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Bacteria
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In high-salt environment- hypertonic conditions
Halobacteria living in the Great Salt Lake-
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Cells must take nutrients in and transport waste out
gas
Some species need oxygen while others require higher than usual concentrations of carbon dioxide
O2 has the greatest impact on microbial growth
O2 enters into cellular reactions, it is transformed into several toxic products
Most cells have developed enzymes that scavenge and neutralize these chemicals
Superoxide dismutase
Catalase
Three catagories
those that can neither use oxygen nor detoxify it
those that do not use oxygen but can detoxify it
those that use oxygen and detoxify it
productus of Oxygen
superoxide ion (O2-)
highly reactive
hydrogen peroxide (H2O2)
toxic to cells and used as a disinfectant
singlet oxygen (O):
an extremely reactive molecule that can damage and destroy a cell by the oxidation of membrane lipids
hydroxyl radicals (OH-)
highly reactive
Categories of Oxygen Requirements
Strict or obligate aerobe
can use gaseous oxygen in its metabolism and possesses the enzymes needed to process toxic oxygen products
cannot grow without oxygen
Facultative anaerobe
an aerobe that does not require oxygen for its metabolism and is capable of growth in the absence of it
Microaerophile
does not grow at normal atmospheric concentrations of oxygen but requires a small amount of it in metabolism
Strict or obligate anaerobes
lack the enzymes for processing toxic oxygen and cannot tolerate any free oxygen in the immediate environment and will die if exposed to it.
Aerotolerant anaerobes
do not utilize oxygen but can survive and grow to a limited extent in its presence
Associations Between Organisms
Symbiotic
Organisms live in close nutritional relationships;
required by one or both members
Mutualism
Obligatory, dependent
both members benefit.
Commensalism
The commensal benefits, other member not
harmed.
example
Staphylococcus aureus and Haemophilus in a "Staph streak" culture
Parasitism
Parasite is dependent and benefits; host harmed
Non symbiotic
Organisms are free-living; relationships not required
for survival.
Antagonism
some members are inhibited or destoryed by others
Synergism
members cooperate and share nutrients