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Chapter 6 – Microbial Growth and Nutrition
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 Carbon is used as an energy source for most organisms
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 Nitrogen is a component in proteins and nucleotides
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 Trace elements are those elements that are required in small quantities
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Distinguish aerobes, anaerobes, aerotolerant anaerobes, facultative anaerobes, and
microaerophiles
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 Aerotolerant anaerobes do not use aerobic metabolism, but can be exposed to oxygen
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 Facultative anaerobes utilize anaerobic respiration or fermentation, in order to survive
without oxygen
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Explain how oxygen can be fatal to organisms, and how organisms protect themselves from toxic
forms of oxygen
 Oxygen can be fatal due to its reactive forms, it is a great oxidizing agent and steals
electrons
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Things like carotenoids, superoxide dismutase (aerobic enzyme)
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Describe nitrogen fixation and discuss its importance
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 Nitrogen fixation is essential for life because it provides nitrogen in a useable form for other
organisms
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Explain how extremes of temperature, pH, and osmotic and hydrostatic pressure limit microbial
growth
 Optimum growth temperature indicates when microbes are capable of growing at the
fastest rate
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 Extremes in osmotic pressure occur when cells are placed in salt water and the cell will lose
water into the surrounding salt water and cause the cells to shrink
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 Quorum sensing is a process, in which the organisms will respond if it gets feedback from a
colony nearby
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 For urinary tract, a catheter is inserted into the bladder through the urethra; in the “clean
catch” method, initial urination washes the urethra, and the specimen is midstream urine
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 Streak Plates involves an inoculating loop to spread an inoculum across the surface of a agar
Petri dish
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The stock sample is diluted
from a series of transfers, and then the final dilution is poured into warm agar
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 Complex media contains different nutrients and the chemical composition is not necessarily
known
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o For example, media high in NaCl (salt) can select for halophiles or salt-tolerant
bacteria
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 Anaerobic Media is media that contains no oxygen and contains reducing agents
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 For instance, cold enrichment allows the growth of cold-tolerant species, by providing
refrigerated conditions
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Discuss the use of animal and cell culture, and low-oxygen culture
 Animal and Cell Culture: Used in case artificial media is inadequate
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 Low-Oxygen Culture: CO2 incubator machines are used to mimic intestinal tract and
respiratory systems
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Contrast refrigeration, deep freezing, and lyophilization as methods of preserving cultures of
microorganisms
 To store living cells, cells metabolism is slowed to prevent accumulation of waste
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 Deep freezing: freezing cells between -50C to -90C for long-term storage
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 Lyophilization: Removing water from solution using vacuum for long term storage
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Cell replicates its chromosome, grows
twice its size, creates new cell wall and divides into 2 daughter cells
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Explain what is meant by the generation time of bacteria
 Time required for bacteria cell to grow and divide
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16
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Each division is typically
30 minutes
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Draw and label a bacterial growth curve
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 Lag phase
o Cells adjust to new environment making enzymes to use the
nutrients given in medium
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 Stationary phase
o Nutrients for the bacteria run out and waste adds up slowing the rate of
reproduction
o Number of dying cells equal number of reproducing cells
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o Membrane Filtration: If a colony is not very dense, a sample is poured in a
membrane filter and undergo incubation
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o Most Probable Number: Statistical estimation technique where the more bacteria
in a sample, the more dilutions are done to reduce the number to 0, then the more
viable are chosen
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Measured with a
spectrophotometer
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 Dry Weight: Organisms that are filtered, dried, and weighed
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Genetic Methods: Isolation of DNA using polymerase chain reaction and hybridization of DNA



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