question

Microbial Growth

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Increase in number of cells, not cell size
Populations
Colonies

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Physical Requirements for Growth

answer

Temperature
pH
Osmotic pressure

question

Chemical requirements for growth

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carbon
nitrogen, sulfur, and phosphorus
trace elements
Oxygen
Organic growth factor

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Teperature requirements

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minimum growth temperature
optimum growth temperature
maximum growth temperature

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Psychotrophs

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Grow between 0^o C and 20-30^o C
cause food spoilage

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pH requirements

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Most bacteria grow between pH 6.5 and 7.5
Molds and yeasts grow between pH 5 and 6

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Acidophiles

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grow in acidic environments

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Osmotic pressure

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hypertonic environments, or an increase in salt or sugar, cause plasmolysis
Extreme or obligate halophiles require high osmotic pressure
Facultative halophiles tolerate high osmotic pressure

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Carbon requirements

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structural organic molecules, energy source
chemoheterotrophs use organic carbon sources
autotrophs use CO₂

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Nitrogen requirements

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in amino acids and proteins
most bacteria decompose proteins
some bacteria use NH₄⁺or NO₃^-
a few bacteria use N₂ in nitrogen fixation

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Sulfur requirements

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in amino acids, thiamine, and biotin
most bacteria decompose proteins
some bacteria use SO₄^2-or H₂S

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Phosphorus requirements

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in DNA, RNA, ATP, and membranes
a source of phosphours is PO₄^3-

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Trace element requirements

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inorganic elements required in small amounts
usually as enzyme cofactors

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Toxic Oxygen

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Singlet Oxygen: ¹O₂^-boosted to a higher-energy state
Superoxide free radicals: O₂^-
Peroxid anion: O₂^2-
Hydroxyl radical (OH)

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Organic Growth Factors

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Organic compounds obtained from the environment
Vitamins, amino acids, purines, and pyrimidines

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Characteristics of Biofilms

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Microbial communities
Form slime or hydrogels
Bacteria attracted by chemicals via quorum sensing
Share nutrients
Sheltered from harmful factors

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Medical cases involving biofilms

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Patients with indwelling catheters received contaminated heparin
Bacterial numbers in contaminated heparin were too low to cause infection
84-421 days after exposure, patients developed infections

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Culture medium

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Nutrients prepared for microbial growth

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Sterile

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No living microbes

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Inoculum

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Introduction of microbes into medium

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Culture

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Microbes growing in/on culture medium

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Agar

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Complex polysaccharide
Used as solidigying agent for culture media in Petri plates, slants, and deeps
Generally not metabolized by microbes
Liquefies at 100^oC
Solidifies at 40^oC

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Chemically defined media

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exact chemical composition is known

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Complex media

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Extracts and digests of yeasts, meat, or plants
Nutrient broth
Nutrient agar

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Reducing media

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Contain chemicals (thioglycolate or oxyrase) that combine O₂
Heated to drive off O₂

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Capnophiles

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Microbes that require high CO₂conditions
CO₂packet
Candle jar

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Biosafety levels

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BSL-1: no special precautions
BSL-2: lab coat, gloves, eye protection
BSL-3: biosafety cabinets to prevent airborne transmission
BSL-4: sealed, negative pressure
Exhaust air is filtered twice

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Differential Media

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Make it easy to distinguish colonies of different microbes

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Selective Media

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Suppress unwanted microbes and encourage desired microbes

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Enrichment Culture

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Encourages growth of desired microbe
Assume a soil sample contains a few phenol-degrading bacteria and thousands of other bacteria
Inoculate phenol-containing culture medium with the soil, and incubate
Transfer 1 ml to another flask of the phenol medium, and incubate
Transfer 1 ml to another flask of the phenol medium, and incubate
Only phenol-metabolizing bacteria will be growing

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Pure Cultures

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A culture containing only one species or strain

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Colony

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A population of cells arising from a single cell or spore or from a group of attached cells

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Colony-forming unit

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Also called CFU
Another name for a colony of bacteria

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Streak plate method

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A method used to isolate pure cultures

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Preserving Bacterial Cultures

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Deep-freezing: -50^oto -95^oC
Lyophilization (freeze-drying): frozen (-54^oto -72^oC) and dehydrated in a vacuum.

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Reproduction in Prokaryotes

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Binary Fission
Budding
Conidiospores (actinomycetes)
Fragmentation of filaments

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Binary fission in bacteria

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Cell elongates and DNA is replicated
Cell wall and plasma membrane begin to constrict
Cross-wall forms, completely seperating the two DNA copies
Cells seperate

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Phases of Bacterial Growth Curve

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Lag Phase
Log Phase
Stationary Phase
Death Phase

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Lag Phase

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First phase in bacterial growth
Intense activity preparing for population growth, but no increase in population

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Log Phase

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Second phase in bacterial growth
Logarithmic, or exponential, increase in population.

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Stationary Phase

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Third stage of bacterial growth
Period of equilibrium; microbial deaths balance production of new cells

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Death Phase

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Fourth and final stage in bacterial growth
Population is decreasing at a logarithmic rate

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Plate Counts

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After incubation, count colonies on plates that have 25-250 colonies

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Most Probable Number

answer

Multiple tube MPN test
Count positive tubes

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Direct Methods of Measuring Microbial Growth

answer

Plate counts
Filtration
MPN
Direct microscopic count

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Indirect Methods of Measuring Microbial Growth

answer

Turbidity
Metabolic activity
Dry weight

Micro: Chapter 6 – Flashcards

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