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68 Cards in this Set
- Front
- Back
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Reproductive strategy of Bacteria and Archaea |
Haploid only Asexual binary fission, budding, filamentous all replicate and segregate genome before division |
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Microbiologists usually study ______ rather than _____ of ________ |
population growth, growth, individual cells |
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cell cycle |
sequence of events from formation of new cell through the next cell division |
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How do bacteria divide? |
binary fission |
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Two pathways that function during cycle |
DNA replication and partition Cytokinesis |
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Beginning of cell cycle |
Replication of genetic material |
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Shape of prokaryotic chromosomes |
circular |
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Origin of replication |
Site at which replication begins, single origin of replication |
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terminus |
site at which replication is terminated |
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replisome |
group of proteins needed for DNA synthesis; parent DNA spools through the replisome as replication occurs |
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protein MreB |
-plays a role in determination of cell shape and movement of chromosomes to opposite cell poles -similar to eukaryotic actin |
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protein FtsZ |
-plays a role in Z ring formation which is essential for septation -similar to eukaryotic tubulin |
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Cytokinesis |
septation -cytoplasm is divided |
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septation |
formation of cross walls between daughter cells |
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Steps of Septation/Cytokinesis |
1) Selection of site for septum formation 2) Assembly of Z ring 3) Linkage of Z ring to plasma membrane 4) Assembly of cell wall synthesizing machinery 5) Constriction of cell and septum formation |
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batch culture |
culture incubated in a closed vessel with a single batch of medium |
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The Growth Curve |
-observed when microorganisms are cultivated in batch culture -usually plotted as logarithm of cell number versus time -usually has 4 distinct phases |
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4 phases of The Growth Curve |
Lag phase Exponential (log) phase Stationary phase Death Phase |
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Lag Phase |
No increase |
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Exponential (log) phase |
maximal rate of division and population growth |
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Stationary phase |
population growth ceases |
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Death phase |
Decline in population size |
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Lag Phase |
-Cell synthesizing new components to replenish spent materials or adapt to new medium -Can be a short phase or sometimes absent |
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Exponential (log) phase |
-rate of growth is constant -population is most uniform in terms of chemical and physical properties |
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Stationary phase |
Total number of viable cells remains constant -may occur because metabolically active cells stop reproducing -may occur because reproductive rate is balanced by death rate -usually at 10^9 cells/ml in bacteria |
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Possible reasons for entry into stationary phase |
nutrient limitation limited oxygen availability toxic waste accumulation critical population density reached |
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Starvation responses |
-morphological changed (endospore formation) -decreases in size -protoplast shrinkage (cell wall shrinkage) -nucleoid condensation -production of starvation proteins -long term survival -increased virulence |
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Death phase |
-cells dying at exponential rate -death, irreversible loss of ability to produce -death rate can slow due to accumulation of resistant cells |
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Generation (doubling) time |
time required for the population to double in size |
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Mean growth rate constant |
-number of generations per unit time -usually expressed as generations per hour |
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Direct cell counts |
-counting chambers -electronic counters -on membrane filter |
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Viable cell counts |
-plating methods -membrane filtration methods |
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Counting chambers |
-useful for counting both eukaryotes and prokaryotes -Petroff-Hausser Counting Chamber |
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Electronic counters |
-useful for large microorganisms and blood cells, but not prokaryotes -microbial suspension forced through small orifice -movement of microbe through orifice impacts electric current that flows through orifice -instances of disruption of current are counted -Coulter Counter |
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Direct counts on membrane filters |
-cells filtered through special membrane that provides dark background for observing cells -cells are stained with fluorescent dyes -useful for counting bacteria -can distinguish living from dead cells with certain dyes |
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Comparison of counting chambers and electronic counters |
-quick, easy, and inexpensive -cannot distinguish living from dead cells |
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CFU |
-Colony Forming Units
-expresses population size |
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Continuous culture system |
maintains cells in log phase at a constant biomass concentration for extended periods
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Chemostat |
rate of incoming medium = rate of removal of medium from vessel -essential nutrient is in limiting quantities |
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Turbidostat |
-regulates the flow rate of media through vessel to maintain a predetermined turbidity or cell density -no limiting nutrient -operates best at high dilution rates |
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Extremophiles |
organisms that grow under harsh conditions that would kill most other organisms |
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Water activity |
-amount of water available to organisms -reduced by interaction with solute molecules (osmotic effect) -reduced by adsorption to surfaces |
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Osmotolerant organisms |
-grow over wide ranges of water activity -use compatible solutes to increase their internal osmotic concentration -have proteins and membranes that require high solute concentrations of stability and activity |
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Halophiles |
require high levels of NaCl to grow |
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pH |
negative logarithm of the hydrogen ion concentration |
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acidophiles |
growth optimum between pH 0 and 5.5 |
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Neutrophiles |
growth optimum between 5.5 and 7 |
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alkalophiles |
growth optimum between pH 8.5 and pH 1.5 |
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acid-shock proteins |
proteins synthesized to provide protection to acidophiles |
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Ways in which microorganisms change their pH of habitat |
-producing acidic or basic waste products -most media contain buffers to prevent growth inhibition |
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3 Cardinal growth temperatures |
-Minimal -Maximal -Optimal |
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Obligate aerobe |
Need oxygen SOD + Catalase + |
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Facultative anaerobe |
Prefer oxygen SOD + Catalase + |
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Aerotolerant anaerobe |
Ignore oxygen SOD + Catalase - |
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Strict anaerobe |
Oxygen is toxic SOD - Catalase - |
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Microaerophile |
<2 -10% oxygen SOD + Catalase +/- (low levels) |
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Protective enzymes that aerobes produce |
-superoxide dismutase (SOD) -catalase |
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Barotolerant organisms |
adversely affected by increased pressure, but not as severely as nontolerant organisms |
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Barophilic organisms |
require or grow more rapidly in the presence of increased pressure |
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Ionizing radiation |
-X rays and gamma rays -mutation --> death -disrupts chemical structure of many molecules, including DNA |
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Ultraviolet (UV) radiation |
-mutations --> death -causes formation of thymine dimers in DNA -DNA damage can be repaired by two mechanisms |
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2 mechanisms in which DNA damage can be repaired |
-photo-reactivation -dark reactivation |
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photo-reactivation |
dimers split in presence of light |
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dark reactivation |
dimers excised and replaced in absence of light |
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Visible light |
-at high intensities generates singlet oxygen (powerful oxidizing agen) -carotenoid pigmnets |
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carotenoid pigments |
protect many light-exposed microorganisms from photooxidation |
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Quorum sensing |
-concentration present allows cells to access population density -microbial communication and cooperation -involves secretion and detection of chemical signals -AHL diffuses across plasma membrane and enters cell at high concentrations -once inside the cell it induces expression of target genes that regulate a variety of functions |
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Acylhomoserine lactone (AHL) |
-an autoinducer molecule produced by many gram negative organisms -concentration present allows cells to access population density -- quorum sensing |
