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Mother cell divides into
two daughter cells
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Microbial growth
the increase in the number of cells, which occurs by cell division
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Binary fission
a cell duplicates its components and divides into two cells
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Budding
cell division in yeast and a few bacteria where a small, new cell develops from the surface of an existing cell and subsequently separates from the parent cell
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Medium
mixture of substances on or in which microorganisms grow
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a. The organisms do not increase significantly in number, but they are metabolically active – growing in size, synthesizing enzymes, and incorporating various molecules from the medium
b. Increase in size and produce large quantities of ATP
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The Log Phase
- a. Population growth occurs at an exponential, or logarithmic (log) rate
- b. Organisms divide at their most rapid rate
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Generation time
regular, genetically determined interval
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Synchronous growth
stair-step pattern
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Nonsynchronous growth
1/20 of cells dividing every minute
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Limiting factor
the rate at which energy can be produced in the form of ATP
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The Stationary Phase
When cell division decreases to the point that new cells are produced at the same rate as old cells die
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The Decline (death) Phase
- a. As conditions in the medium become less and less supportive of cell division, many cells lose their ability to divide, and thus the cells die
- b. Decreases at a logarithmic rate
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Involution
cells assume a variety of unusual shapes, which makes them difficult to identify
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Colony
all the descendants of an original cell
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Agar plate
a Petri dish containing a nutrient medium solidified with agar (a complex polysaccharide extracted from certain marine algae)
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Countable number of colonies
is 30 – 300 per plate
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Direct Microscopic Counts
Uses a specially calibrated, etched glass slide called a Petroff-Hausser counting chamber (hemocytometer)
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1. When samples contain too few organisms to give reliable measures of population size (food and water sanitation studies)
2. Dilute to where some test tubes contain 1 organisms and some none (testing water purity)
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Filtration
A known volume of water or air is drawn through a filter with holes too small to allow passage of bacteria
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Turbidity
indicates presence of organisms
- a. Spectrophotometer
- b. Subject to error when cultures contain fewer than 1 million cells per milliliter
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For almost any substance, there is some microbe that can metabolize it as a nutrient; for almost any environmental change, there is some microbe that can survive the change
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Physical Factors
Include pH, temperature, oxygen concentration, moisture, hydrostatic pressure, osmotic pressure, and radiation
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optimum pH
the pH at which microbes grow best
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acidophiles
grow best at a pH of 0.1 to 5.4 (Lactobacillus)
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neutrophiles
exist from pH 5.4 to 8.0
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alkaliphiles
exist from pH 7.0 to 11.5 (Vibrio cholera grows best at pH 9.0)
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Obligate
the organism must have the specified environmental condition
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Facultative
the organism is able to adjust to and tolerate the environmental condition, but it can also live in other conditions
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Psychrophiles
(cold-loving organisms) grow best at temperatures of 15* to 20*C, although some live quite well at 0*C
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Obligate psychrophiles
(Bacillus globisporus) cannot grow above 20*C
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Faciltative psychrophiles
(Xanthomonas pharmicola) grows best below 20*C but can grow above that temperature
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Mesophiles
grow best at temperatures between 25* and 40*C.
Human pathogens
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Thermoduric organisms
ordinarily live as mesophiles but can withstand short periods of exposure to high temperatures
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Thermophiles
(heat-loving organisms) grow best from 50* to 60*C
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Obligate thermophiles
can grow only at temperatures above 37*C
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Facultative thermophiles
can grow both above and below 37*C
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Minimum growth temperature
the lowest temperature at which cells can divide
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Maximum growth temperature
the highest temperature at which cells can divide
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Optimum growth temperature
the temperature at which cells divide most rapidly
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Obligate aerobes
(Pseudomonas) must have free oxygen for aerobic respiration
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Obligate anerobes
(Clostridium botulinum, C. tetani, and Bacteroides) are killed by free oxygen
a. Killed by superoxide
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Microaerophiles
appear to grow best in the presence of a small amount of free oxygen
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Capnophiles
carbon dioxide-loving organisms
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Facultative anaerobes
ordinarily carry on aerobic metabolism when oxygen is present, but they shift to anaerobic metabolism when oxygen is absent (Staphylococcus and E. Coli)
Have the most complex enzyme systems
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Aerotolerant anaerobes
can survive in the presence of oxygen but do not use it in their metabolism
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Hydrostatic Pressure
Pressure exerted by standing water, in proportion to its depth
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Barophiles
bacteria that lice at high pressures, but die in atmospheric pressure
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Plasmolysis
shrinking of the cell
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Halophiles
salt-loving organisms
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Bacteria which can withstand high levels of radiation may be valuable for use in cleaning up contaminated sites
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Fastidious
microbes that have special nutritional needs that can be difficult to meet in the laboratory
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Photoautotrophic organism reduce carbon dioxide to
glucose and other organic molecules
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Some microbes reduce nitrate ions to
amino groups
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Some organisms synthesize sulfur-containing amino acids and they use phosphorus to
synthesize ATP, phospholipids, and nucleic acids
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Vitamin
an organic substance that an organism requires in small amounts and that is typically used as a coenzyme
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Nutritional Complexity
The number of nutrients it must obtain to grow
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Extracellular enzymes
usually produces by Gram-positive rods, which act in the medium around the organism
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Periplasmic enzymes
usually produced by Gram-negative organisms, which act in the periplasmic space
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Many organisms adjust the rate at which _____________ and the rate at which _____________ to fit the availability of the lease plentiful nutrient
they metabolize nutrients
they synthesize molecules required for growth
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The formation of endospores occurs in _______ .
Bacillus, Clostridium, and a few other Gram-positive genera.
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Bacteria that form endospores generally do so during the __________ in response to environmental, metabolic, and cell cycle signals
stationary phase
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Sporulation
Protective or survival mechanism, not a means of reproduction
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Core
living part of the endospore
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Endospore septum
consisting of a cell membrane but lacking a cell wall, grows around the core, enclosing it in a double thickness of cell membrane (synthesizes peptidoglycan)
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Cortex
protects the core against changes in osmotic pressure (drying)
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Spore coat
is laid down around the cortex by the mother cell
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Exosporium
a lipid-protein membrane
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Germination
a spore returns to its vegetative state
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Germination Activation
usually requires some traumatic agent such as low pH or heat, which damages the coat
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Germination proper
requires water and a germination agent that penetrates the damaged coat
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Germination Outgrowth
occurs in a medium with adequate nutrients. Proteins and RNA are synthesized, and in about an hour, DNA synthesis begins
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Cysts
spherical, thick-walled cells, that resemble endospores
Metabolically inactive and resist drying
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Conidia
chains of aerial spores with thick outer walls
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Pure culture
a culture that contains only a single species of organism
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1. Makes use of serial dilutions
- a. A series of dilutions are made such that the final dilution contains about 1,000 organisms
- b. It is particularly useful for growing microaerophiles that cannot tolerate exposure to oxygen in the air at the surface of the medium
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Synthetic medium
a medium prepared in the laboratory from materials of precise or reasonable well-defined composition
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Defined synthetic medium
one that contains known specific kinds and amounts of chemical substances
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Complex medium (chemically nondefined medium)
contains reasonable familiar materials but varies slightly in chemical composition from batch to batch
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Peptone
a product of enzyme digestion of proteins, common ingredient of complex medium
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Casein hydrolysate
made from mil protein, contains many amino acids and is used to enrich certain media
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Selective medium
one that encourages the growth of some organisms but suppresses the growth of others (SPS agar)
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Differential medium
has a constituent that causes an observable change ( a color change or a change in pH) in the medium when a particular biochemical reaction occurs
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Enrichment medium
contains special nutrients that allow growth of a particular organism that might not otherwise be present in sufficient numbers to allow it to be isolated and identified
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Stock culture
one an organism has been isolated, it can be maintained indefinitely in a pure culture
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Aseptic techniques
minimize the chances that cultures will be contaminated by organisms from the environment or that organism, especially pathogens, will escape into the environment
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Preserved Cultures
A culture in which organisms are maintained in a dormant state
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Lyophilization
freeze-drying
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Reference culture
a preserved culture that maintains the organisms with the characteristics as originally defined
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