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32 Cards in this Set
- Front
- Back
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What is a biofilm and what advantages do they provide? |
layer of bacterial growth (can be multiple species) that secrete sugars that stick to a surface, making them hard to removeProvides resistance to antimicrobialsCan escape to other sites |
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How do most Bacteria reproduce? |
Binary fissionCell elongates as new material is synthesizedReplicates chromosomeSeparates newly formed DNA so there is one chromosome in each halfSeptum forms, dividing into two progency cells, each with own chromosome + complement of other cellular constituents |
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What are some other ways that Microorganisms reproduce? |
Some form by budding, where bacteria undergo multiple fission and held within the cell wall of the parent cell until releasedForm multinucleoid filaments that eventually divide to form uninucleoid spores that are dispersed like fungi |
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What are the steps in cell division? |
Three phasesPeriod of growth after cell is born (like G1) Chromosome replication and partitioning periodLike S and M phaseCytokinesis, where septum is formedNo G2 phase |
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How is a chromosome replicated? |
Circular chromosomeSingle site where replication starts called originEnds at terminusEarly in cell cycle, origin and terminus move to midcell and group of proteins assembleReplisome = dna synthesizing machinery, where DNA replication proceeds in both directions from the originTakes about 40 minutes to replicate DNA |
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How is new cell wall formed? |
Peptidoglycan synthesis starts in cytoplasm w UDP attaching to NAGUDP-NAG convert to UDP-NAMNAM is transferred from UDP to bactoprenol = carrier embedded in plasma membraneNAG is attached to bactoprenol-NAM → bactoprenol-NAM-NAG (aka lipid II)Dividsome protein FtsW lips lipid II across PM so that NAM-NAG is available for insertionAutolysins located at divisome degrade bonds in existing peptidoglycans, allowing insertion of new NAM-NAG unitsPreexisting peptidoglycan needs to be severed to allow newly synthesized peptidoglycan to form |
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Know what makes a bacillus cell rodlike. And why Cocci are spheres. |
Cell wall constrains turgor pressure preventing cell from swelling and burstingTurgor pressure = force pushing against cell wall, determined by osmolarity of cytoplasmic contentsCocciNew peptidoglycan forms only at the central septumWhen dividing, the daughter cells have one old half of cell wall, one newBacillus Prior to division and during growth, new cell wall is made along the side of the cell but not at the poles → elongation (using MreB)FtsZ polymerization forms Z ring and new cell wall growth is confined to midcellRod-shaped daughter cells are formed with one new pole and one old pole |
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Know what makes a vibrio cell crescent shaped? |
MreB + FtsZ are used to produce cytoskeletal protein called crescentinLocalizes to one side of cell, where it slows the insertion of new peptidoglycan units into peptidoglycan sacculus |
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Know the different kinds of media covered in lecture. |
Blood agar - for hemolytic vs nonhemolytic bacteriaEMB agar - inhibit growth of gram-positive bacteraMacConkey (MAC) agar - inhibits growth of gram-positive bacteriaMannitol salt agar - selects for staphylococci |
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Streak plate - |
cells transferred to edge of agar plate; After first sector is streaked, the inoculating loop is sterilized and an inoculum for second sector is obtained from first sectorBasically, = dilution |
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Spread plate - |
small volume of diluted mixture containing around 25-250 cells is transferred to center and spread evenlyDevelop into isolated coloniesDilutions prepared by serial dilutions |
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Pour plate - |
Original sample is serially diluted to reduce microbial population sufficiently to obtain separate colonies when platingMixed with liquid agar; cells become fixed when agar hardens |
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Know what is meant by a pure culture. |
Single strand of cells arising from a single ancestor |
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Why is it important that we study pure cultures? |
Enables study of single organism in mixed cultureAll cells genetically identical |
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Know the different phases of growth in a batch culture. |
Lag, exponential, stationary then deathPlotted as log of cell number vs timeDeath - nutrient limitation, toxic waste accumulation, critical population density reached |
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Understand the mathematics behind cell growth. |
Population calculation = initial number * 2n, where n = number of divisions |
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Microscopic counts |
Microbial populations must be relatively large and evenly dispersed to determine size accuratelyOnly small volume is sampledMovingHuman errorCannot distinguish between live and dead cells without stainsDebris |
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Automatic cell counts - |
flow cytometer; uses laser beams + dyes + electronicsMore expensiveMachine also has trouble discerning between live + dead |
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Viable counts |
Serial dilutions; count only cells that are able to reproduce when culturedBiased sample portionsHuman error If clumps of cells are not broken up and microorganisms well-dispersed, then inaccurate countsMay kill cells by plating, so that plate counts will be artificially lowLeads to great plate count anomaly: Number of cells observed by microscopy is often much higher than the population size determined by plate countsB.c microscopic methods count dead cells; viable methods do not |
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Turbidimetric methods |
SpectrophotometryAbsorbance is linearly related to cell concentration at absorbance levels less than about 0.5 |
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Know the different classes of extremophiles. |
Halophiles - salt tolerantOsmophiles - organisms that live in environments high in sugarXerophiles - very dry conditionsAcidophileNeutrophileAlkaliphilePsychrophile - cold temperaturesPsychotolerant Mesophile - warmThermophilesHyperthermophilesPiezophiles - high pressures |
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Know what is meant by water activity. |
Vapor pressure of air in equilibrium Equivalent to ratio of solution’s vapor pressure to that of pure water1.000 = pure water, 0.700 = theoretical limit for life |
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Know what is meant by, hypertonic, hypotonic, isotonic. |
Hypotonic - concentration is higher inside cellHypertonic - concentration is higher outside cellCells in distilled water → swell + burstCells in concentrate → shrink + shrivel |
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How do cells adapt to high salinity? Acid? Base? High temperature? Low temperature? |
Salinity - can increase internal solute concentration by Pumping inorganic ions from environment into cellSynthesis or concentration of organic solutes |
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Be able to identify the different oxygen requirements of a cell. |
Aerobes - require oxygenAnaerobes - killed by exposure to oxygenFacultative organisms - can live with or without oxygenAerotolerant anaerobes - can tolerate oxygen but don’t use itMicroaerophiles - use oxygen at only low levels |
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What is a reactive oxygen species (toxic form of oxygen) and how do cells protect themselves? |
Superoxide, hydrogen peroxides and hydroxyl radicalsSuperoxide reductase, catalase, superoxide dismutase, peroxidase |
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What are two ways we define a microbial species? |
More accepted: > 97% 16S rRNA sequence identity70% DNA hybridization |
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Why is it hard to define a microbial species? |
Millions upon millions of different “species” Most never isolated/culturedHuge genetic diversity within microbial “species” |
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What is the most commonly used definition of a microbial species? |
>97% 16S rRNA sequence identity |
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What is an OTU? |
Operational taxonomic unit - used instead of the word species |
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What is lateral gene transfer? |
The transfer of genetic material from one organism to another that is not its offspringInitiated by phage infection, conjugation and transformationTransfered genes can be integrated directly into chromosome/plasmid |
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How does Speciation Occur? |
Temporary reproductive isolation/limited gene flowThis enables the accumulation of genetic diversityResults in permanent reproductive isolation/no gene flow |
