Ch.4 Flashcards
Pure Culture
- population of cells derived from a single cell
- allows study of a single species
- Organisms may behave differently than in nature
- Only about 1% of microorganisms can be cultured
- Pure culture obtained using aseptic technique: Minimizes accidental introduction of other organisms
Which technique is used to isolate bacteria from a mixed culture into a pure culture?
Streak-plate method
- Simplest, most commonly used method for isolating
- Reduces number of cells with each series of streaks
- Separated cells form distinct, isolated colonies
Which polysaccharide derived from Red Seaweed is used to solidify media for bacterial growth?
- Agar used to solidify medium
– Few microbes can degrade
– Not destroyed by high temperatures and can be sterilized
– Liquefies above 95 C
– Solidifies below 45 C
– Solid over temperature range for most microbial growth
Why is agar preferred over gelatin?
for its non-nutritive qualities, which allow for bacterial growth without being digested
In the growth curve of a bacterial population, at which phase are the bacteria rapidly increasing?
Exponential (log) phase:
- Cells divide at constant rate
– Generation time measured
– Most sensitive to antibiotics
During which phase of the bacterial growth curve does the total number of viable (live) cells decline?
Death phase:
- Total number of viable cells decreases at constant rate
- Exponential, but slower than cell growth
thermophile
- 45 C to 70 C
- love hot tempertures –> common in hot springs and compost heaps
What happens to proteins inside of bacteria that cannot survive these types of conditions?
- Proteins of thermophiles resist denaturing
- Thermostability comes from amino acid sequence
- Number and position of bonds that determine structure
obligate aerobe
organism requires O2 to grow
Facultative aerobes
use O2, but don’t require it
Obligate anaerobes
cannot use O2
Aerotolerant anaerobes
obligate fermenters (can grow in O2, but they don’t use it)
How do high concentrations of salt and sugar in food help preserve food?
- All microorganisms require water for growth
- Dissolved salts, sugars make water unavailable to cell
- Salt, sugar used to preserve food
- If solute concentration is higher outside of cell, water diffuses out (osmosis)
- Some microbes withstand or even require high salt
Which are the 6 major elements that are needed to build organic molecules and biological bodies?
Carbon
Hydrogen
Nitrogen
Oxygen
Phosphorus
Sulfur
What is the definition of “growth factors” when it comes to bacterial growth?
organic molecules that an organism cannot synthesize; must be present in the environment
- Growth factor requirements reflect biosynthetic capabilities
– Most E. coli strains synthesize all cellular components from glucose; no growth factors needed
– Neisseria species are fastidious; they require numerous growth factors, including vitamins and amino acids