Intro To Prokaryotes #3 Flashcards
what is the generation (doubling) time ?
time required for the population to double in size
how can microbial growth be measured ? (2)
by changes in number of cells in a population, or by measuring the changes in mass of population
what is turbidity ?
of a culture, often expressed as optical density at a particular wavelength (OD600nm)
cloudiness of a liquid
What are the 2 types of elements of life?
- Macroelements (macronutrients)
- Micronutrients (trace elements)
What are the micronutrients required in trace amounts?
Mn, Zn, Co, Mo, Ni, Cu (serve as enzymes cofactors)
What are the macroelements required in large amounts?
C, H, O, N, P, S (found in organic molecules)
Ca, K, Fe, Mg (cations = enzyme catalysis)
What is a prototroph?
a microorganism that requires the same nutrients as most of the naturally-occurring members of its species
What is an auxotroph?
a mutated prototroph that is no longer able to synthesise a molecule necessary for growth & reproduction, molecule needs to be supplied, unable to produce growth factors it needs
what are growth factors ?
organic compounds, essential cell components that cell can’t synthesise, supplied by env
What are the 3 classes of growth factors?
- Amino Acids
- Purines & Pyrimidines
- Vitamins
VAP = classes of growth factors
what are two types of media (classified according to chemical composition)
defined (synthetic), complex
what are 3 types of media (classified according to physical nature)
- liquid,
- semisolid,
- solid
what are 4 types of media (classified according to function)
- supportive (general purpose),
- enriched,
- selective,
- differential
what is minimal medium ?
a special kind of defined medium containing minimal nutrient requirements for growth
what are peptones ?
protein hydrolysates prepared by partial digestion of various protein sources
what are extracts ?
in terms of media
aqueous extracts, usually of beef or yeast
what is agar?
sulphated polysaccharide used to solidify liquid media; most microorganisms can’t degrade it
what is supportive (general purpose) media ?
(with examples)
support the growth of many types of microorgs
(e.g. tryptic soy agar, nutrient agar)
what is enriched media ?
(with an example)
general purpose media supplemented by blood or other special nutrients
e.g. blood agar
what is blood agar?
media categories, and what is it used for
- both an enriched & differential medium,
- used to isolate fastidious orgs & detect haemolytic activity
what are selective media ?
with an example
- favour the growth of some microorganisms and
- inhibit the growth of others
(e.g. macconkey agar)
how does macconkey agar work?
selects for gram- negative bacteria by inhibiting the growth of gram-positive bacteria
what is differential media ?
provide 2 examples with explanations
distinguish between different groups of microorganisms based on biological characteristics
e.g. blood agar (haemolytic vs non-haemolytic bacteria)
e.g. macconkey agar (see colour difference between colonies of lactose fermenters vs lactose non fermenters) = is a selective & differential medium (only grows gram-negative)
what are microaerophiles ?
requires 2-10% O2
what is the difference between facultative anaerobes & aerotolerant anaerobes?
facultative = don’t require O2 but grow better in its presence
aerotolerant = grow with or without O2, not killed by O2
what are 2 viable counting methods?
- spread technique
- pour plate technique
describe what you would do to get a viable count of a culture
- spread diluted sample over solid agar surface OR mixed with agar and poured into petri dish
- incubate
- determine number of organisms by counting the number of colonies multiplied by the dilution factor
results expressed as CFU (colony forming units)
what are 3 methods to measure cell mass?
- dry weight
- quantity of a particular cell constituent (useful if amount of substance in each cell is constant)
- turbidometric methods (light scattering by cells) = best one
