Test Questions on Chapter 6 – Microbiology – Flashcards

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microbial growth
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  • referring to the increase in size of a population of microbes
  • not individual microbe size- but individual reproduction contributes to growth
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three things that all cells need for metabolism
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  • a carbon source
  • a source of energy
  • a source of electrons or hydrogen atoms
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autotrophs
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  • organisms that utilize an inorganic source of carbon (ie: CO2) as their sole source of carbon
  • these acquire electrons or hydrogen atoms from inorganic molecules=lithotrophs
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heterotrophs
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  • catabolize reduced organic molecules (ie: proteins, carbs, amino acids, and/or fatty acids) they acquire from other organisms
  • these acquire electrons from the same organic molecules that provide them carbon=organotrophs
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chemotrophs
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organisms that acquire energy from redox reactions involving inorganic and organic chemicals
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phototrophs
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organisms that use light as their energy source
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four basic groups of organisms based on their energy and carb sources:
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  • photoautotrophs- light and CO2
  • chemoautotrophs- redox rxns and CO2
  • photoheterotrophs- light and organic molecules
  • chemoheterotrophs- redox reactions and organic molecules
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limiting nutrient
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  • a chemical that is needed in order to continue metabolism
  • lack of this nutrient interrupts metabolism
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organotrophs
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(heterotrophs) acquire their electrons from the same organic molecules that provide them carbon
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lithotrops
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(autotrophs) acquire electrons or hydrogen atoms from inorganic molecules
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obligate aerobes
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  • oxygen is essential for these organisms because it serves as the final electron acceptor of electron transport chains
  • algae, most fungi and protozoa, and many prokaryotes
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obligate anaerobes
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oxygen is a "deadly poison" for these organisms
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four toxic forms of oxygen
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  • singlet oxygen: neutralized by pigments called carotenoids
  • superoxide radical: detoxified by superoxide dismutase
  • peroxide anion: detoxified by catalase or peroxidase
  • hydroxyl radical: most reactive of the toxic forms of O2
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singlet oxygen
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  • molecular oxygen with electrons that have been boosted to a higher energy state, typically during aerobic metabolism
  • very reactive oxidizing agent.
  • human WBC's use it to oxidize pathogens
  • phototrophs contain pigments called "carotenoids" that prevent toxicity by removing the excess energy of singlet oxygen
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superoxide radical
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  • formed during the incomplete reduction of O2 during electron transport in aerobes and during metabolism by anaerobes in the presence of O2
  • so reactive and toxic that aerobes must produce enzymes called "superoxide dismutases"
  • anaerobes lack superoxide dismutase, therefore susceptible to this particular O2 toxicity
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peroxide anion
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  • another highly reactive oxidant contained within hydrogen peroxide that is formed during reactions catalyzed by superoxide dismutase
  • peroxide anion is what makes hydrogen peroxide an antimicrobial
  • aerobes contain either catalase or peroxidase in order to detoxify
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hydroxyl radical
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  • most toxic form of oxygen
  • result from ionizing radiation and from the incomplete reduction of hydrogen peroxide
  • this does not accumulate in aerobic cells (because of catalase and peroxidase)
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facultative anaerobes
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  • aerobes which can maintain life via fermentation or anaerobic respiration, though their metabolic efficiency is often reduced in the absence of oxygen
  • a few yeasts and numerous prokaryotes
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aerotolerant anaerobes
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  • microorganisms which prefer anerobic conditions but can tolerate low levels of oxygen
  • they do not use aerobic metabolism
  • tolerate oxygen by having some of the enzymes that detoxify oxygen's poisonious forms
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microaerophiles
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  • organisms which require low levels of oxygen
  • ie: H. pylori requires oxygen levels of 2 -10%
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nitrogen 

(for growth requirements)

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  • essential element for growth
  • contained in many organic compounds including the amine group in amino acids and part of nucleotide bases
  • often a growth-limiting nutrient for many organisms
  • acquired from organic and inorganic compounds
  • most photosynthetic organisms can reduce nitrate to ammonia (which can then be used for biosynthesis)
  • some bacteria capable of nitrogen fixation
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nitrogen fixation
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  • process of reducing nitrogen gas (N2) to ammonia (NH3)
  • few bacteria are capable of this process, notably many cyanobacteria, as well as Rhizobium
  • essential for life on earth because nitrogen-fixers provide nitrogen in a usable form to other organisms
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phosphorus

(for growth requirements)

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component of phospholipid membranes, DNA, RNA, and some proteins
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sulfur

(for growth requirements)

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  • component of sulfur-containing amino acids
  • these bind to one another via disulfide bonds that are critical to the tertiary structure of proteins
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lithotrophic photoautotrophs
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  • microorganisms that can synthesize all of their metabolic and structural needs from inorganic nutrients
  • they have every enzyme and cofactor needed to produce all of their cellular components
  • includes: algae and photosynthetic bacteria
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growth factors
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  • note: most organisms can not synthesize all of their needed organic chemicals
  • definition: organic chemical such as a vitamin required in very small amounts for metabolism
  • recall: vitamins constitute all or part of many coenzymes
  • other examples: some amino acids, purines, pyrimidines, cholesterol, NADH, and heme
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temperature

(for growth requirements)

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  • effects the 3-D configurations of biological molecules
  • can denature proteins
  • can alter temperature-sensitive hydrogen bonds of proteins
  • can also effect lipids within membranes
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minimum growth temperature
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the lowest temperature at which an organism is able to conduct metabolism
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maximum growth temperature
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highest temperature at which an organism continues to metabolize
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optimum growth temperature
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temperature at which an organism's metabolic activities produce the highest growth rate
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psychrophiles
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microorganisms which grow best at temperatures below 15*C
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mesophiles
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  • organisms that grow best between temperatures ranging from 20*C - 40*C
  • note: body temperature is 37*C, so most human pathogens are mesophiles
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thermoduric organisms
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mesophiles that can survive brief periods at higher temperatures
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thermophiles
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organisms which grow at temperatures above 45*C in habitats such as compost piles and hot springs
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hyperthermophiles
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usually archea, grow in water above 80*C, others live at temperatures above 100*C
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pH growth requirements
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organisms are sensitive to changes in acidity because hydrogen ions and hydroxyl ions interfere with hydrogen bonding within proteins and nucleic acids
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neutrophiles
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  • these grow best in a narrow range around neutral pH, usually between 6.5-7.5
  • includes: most bacteria and protozoa, inluding pathogens
  • note: this is the pH range for most of the tissues and organs within the human body
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acidophiles
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  • organisms which grow best in an acidic habitats
  • obligate acidophiles: require an acidic environment and die if the pH approaches 7
  • acid-tolerant microbes: merely survive in acid without preferring it
  • ie: H. pylori
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alkalinophiles
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live in alkaline soils and water up to pH 11.5
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osmotic pressure
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  • the pressure exerted on a semipermeable membrane by a solution containing solutes
  • higher concentration of solutes = hypertonic
  • lower concentration of solutes = hypotonic
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crenation
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shriveling of a cell in a hypertonic environment
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obligate halophiles
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  • microorganism requiring high osmotic pressure
  • ie: Great salt lake or smaller salt ponds
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facultative halophiles
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microbes that do not require high salt concentrations but can tolerate them
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hydrostatic pressure
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  • water exerts pressure in proportion to its depth
  • for every additional 10 m of depth, water pressure increases 1 atmosphere (atm)
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barophiles
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  • organisms that live under extreme hydrostatic pressure
  • their membranes and enzymes depend on pressure to maintain their three dimensional shapes
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antagonistic relationships
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relationships in which one organism harms or kills another organism
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synergistic relationships
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individual members of an association cooperate such that each receives benefits that exceed those that would result if each lived by itself, even though each member could live separately
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symbiotic relationships
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organisms live in such close nutritional or physical contact that they became interdependent
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biofilms
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  • complex relationships among numerous microorganisms, often different species, attached to surfaces
  • they develop an extracellular matrix, composed of DNA, proteins, and primarily the tangled fibers of polysaccharides the cell's glycocalyces
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quorom sensing
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process by which bacteria respond to changes in microbial density by utilizing signal and receptor molecules
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inoculum
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  • sample of microorganisms
  • usually placed in media in order to culture
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medium
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collection of nutrients used for cultivating microorganisms
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culture
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  • can refer to either the act of cultivating organisms (verb)
  • or the microorganisms cultivated (noun)
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colonies
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cultures that are visible on the surface of solid media
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clinical specimen
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  • sample of human material, such as feces or blood, that is examined or tested for the presence of microbes
  • often transported in special transport media
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pure cultures
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  • cultures composed of cells arising from a single progenitor
  • aka "axenic"
  • the progenitor=CFU's
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CFU's
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  • colony forming units
  • a single cell or related cells that produce a colony
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defined medium
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  • aka synthetic medium
  • one in which the exact chemical composition is known
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fastidious organisms
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  • these require a relatively large number of growth factors
  • these can be used to test for presence of the specific growth factors needed by the organism (living assays)
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complex media
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  • culturing media that contains nutrients released by the partial digestion of yeast, soy, beef, or other proteins; thus the exact chemical composition is unknown
  • most chemoheterotrophs, including pathogens, are grown in this type of media
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selective media
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typically contain substances that either favor the growth of particular microorganisms or inhibit the growth of unwanted ones
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differential media
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formulated such that either the presence of visual changes of the medium or differences in the appearance of colonies help microbiologists differentiate among different kinds of bacteria growing on the medium
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MacConkey agar
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  • both selective and differential medium
  • inhibits the growth of Gram-positive bacteria
  • differentiates lactose-fermenting from non-lactose-fermenting Gram-negative bacteria
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reducing media
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  • special media that provides better anaerobic culturing conditions
  • contains compounds such as sodium thioglycollate that chemically combine with free oxygen and remove it from the medium
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transport media
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media used by hospital personnel to carry clinical specimens of feces, urine, saliva, sputum, blood, and other bodily fluids in such a way that people are not infected and the specimens are not contaminated
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animal and cell culture
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living tissue required to grow and cultivate specific types of microorganisms
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carbon dioxide incubators
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  • machines that electronically monitor and control CO2 levels
  • these provide atmospheres that mimic the environments of the intestinal tract, the respiratory tract, and other body tissues 
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candle jar
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  • smaller and less expensive alternative to CO2 incubator
  • culture plates are sealed in a jar with a lit candle, the flame consumes most of the O2 replacing it with CO2 and the candle extinguishes itself
  • creates an environment suitable for aerotolerant anaerobes, microaerophiles, and capnophiles
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capnophiles
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microorganisms that grow best with high levels of carbon dioxide in addition to low levels of oxygen
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enrichment culture
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  • technique used to enhance the growth of less abundant microorganisms by using a selective medium
  • designed to increase very small numbers of a chosen microbe to observable levels
  • method introduced by Beijernick in the late 1800's
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cold enrichment
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  • incubation of a specimen in a refrigerator to enhance the growth of cold-tolerant species
  • ie: Vibrio cholerae
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refrigeration

(for storage)

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best technique for storing cultures for short periods of time
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deep-freezing
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  • long-term storage of bacterial cultures at temperatures ranging from -50*C to -95*C
  • stores for several years
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lyophilization
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  • removal of water from a frozen culture or other substance by means of vacuum pressure
  • used for long-term storage preservation of food and cells
  • typically can be stored for decades
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binary fission
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  • reproduction process of most unicellular microorganisms
  • process in which a cell grows to twice its normal size and divides in half to produce two daughter cells of equal size
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binary fission steps
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  1. cell replicates its chromosomes and attaches to the cell membrane
  2. cell elongates and growth between attachment sites pushes the chromosomes apart
  3. the cell forms a new cytoplasmic membrane and wall (septum) across the midline
  4. when the septum is complete, the daughter cells may remain attached or may separate completely
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logarithmic growth
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  • aka exponential growth
  • increase of size of a microbial population in which the number of cells doubles in a fixed interval of time
  • to calculate the number of cells in a population, we multiply the original number of cells by 2n
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generation time
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  • the time required for a bacterial cell to grow and divide
  • the time required for a population of cells to double in number
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growth curve
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a graph that plots the number of organisms in a growing population over time
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semilogarithmic graph
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only one axis uses a log scale
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lag phase
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  • cells are adjusting to their new environment
  • most cells do not reproduce immediately, but instead actively synthesize enzymes to utilize novel nutrients in the medium
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log phase
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  • population increases logarithmically
  • reproduction rate reaches a constant as DNA and protein syntheses are maximized
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stationary phase
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  • the number of dying cells equals the number of cells being produced
  • the size of the population remains constant
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death phase
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  • cells die at a faster rate than those being produced
  • occurs as nutrients become more limited and waste products increase
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chemostat
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  • an open system in which fresh medium is continuously supplied while an equal amount of old medium (containing microbes) is removed
  • done to maintain a particular phase of microbial growth
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serial dilution
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a stepwise dilution of a liquid culture in which the dilution factor at each step is constant

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viable plate count
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  • estimation of the size of a microbial population based on the number of colonies formed when diluted samples are plated onto agar media
  • count the colonies on a plate with 25-250 colonies and multiply by the reciprocal of the dilution ratio to estimate the number of bacteria per ml of the original culture
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membrane filtration
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  • technique used if the population density is very small
  • large sample is poured through a filter small enough to trap cells
  • the number of colonies trapped on the filter is equal to the number of CFU's in the original large sample
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most probable number (MPN)
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  • statistical estimation of the size of a microbial population based upon the dilution of a sample required to eliminate microbial growth
  • based on the fact that the more bacteria there are in a sample, the more dilutions are required to reduce their number to zero
  • number of tubes showing growth in each dilution set is used to enter into an MPN table
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Petroff-Hausser counting chamber
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  • sample is placed onto a cell counter, which is a glass slide composed of an etched grid positioned beneath a glass cover slip
  • calculated by multiplying the number of bacteria per square by 1,250,000
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Coulter counter
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  • a device that directly counts cells as they interrupt an electrical current flowing across a narrow tube held in front of an electronic detector
  • flow cytometry is a variation of the Coulter counter which uses a light-sensitive detector to record changes in light transmission through the tube as cells pass
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metabolic activity
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  • indirect counting method
  • under standard temperature conditions, the rate at which a population of cells utilizes and produces wastes depends on their number
  • once the metabolic rate is established, scientists can indirectly estimate the number of cells in a culture
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dry weight
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  • abundance of filamentous microorganisms are difficult to measure by direct methods
  • instead these are filtered from their culture medium, dried and weighed
  • suitable for broth cultures
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turbidity
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  • as bacteria reproduce in a broth culture, the broth often becomes turbid (cloudy) 
  • the more bacteria within a broth, the more light will be absorbed and scattered, and less light will pass through and strike a light-sensitive detector
  • only accurate if cells are suspended uniformly (no sediment)
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genetic methods
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scientists can isolate unique DNA sequences representing unculturable prokaryotic species using genetic techniques such as polymerase chain reaction (PCR) and hybridization of DNA that codes for ribosomal RNA
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