lecture 8-10 Flashcards
Chemoautotrophs / Chemolithotrophs
energy from inorganic compounds
(litho = rocks)
Chemoheterotrophs / Chemoorganotrophs
energy from organic compounds
microbes are classified based on their…
carbon and energy acquisition
Autotrophs
– Photoautotrophs
– Chemoautotrophs (chemolithotrophs)
Heterotrophs
– Photoheterotrophs
– Chemoheterotrophs (or chemoorganotrophs)
Nitrogen fixers (called ______) have
______________; converts inorganic N2 to
ammonium ions (NH4+)
diazotrophs, nitrogenase enzyme
Most bacteria divide by
binary fission
Liquid media or broth:
cells are in suspension
Solid media:
usually gelled/solidified with agar
Cell grows as Colony Forming Units (CFU); a colony =
a visible group of microbial cells that developed from
the same mother cell
Complex/rich media:
nutrient rich; exact composition is poorly defined
Minimal defined media:
contain only those nutrients that are essential for growth of a given microbe
Enriched media:
complex media to which specific factors are added; the microbe is not capable of making them but needs them to grow
Selective media:
favour the growth of one organism over another.
Differential media:
exploit biochemical/physiological differences between two species that grow equally well (in the medium)
pure cultures isolated by two techniques:
Dilution streaking and Spread plating
Lag phase
- Bacteria adapt themselves to growth conditions
- Bacteria are maturing and not yet
able to divide - Synthesis of RNA, enzymes and
other molecules occurs
four phases of growth:
◦ lag, exponential/logarithmic (log), stationary, death
Exponential/Logarithmic (log) phase
- Characterized by cell doubling
- Log growth cannot continue
indefinitely as medium is depleted of
nutrients and enriched with wastes in
batch cultures
Exponential/Logarithmic (log) phase can be split into two phases:
early and late
Early exponential phase:
cells growing at the maximum rate (physiologically) possible based on conditions available
Late exponential phase:
slowing of growth rate due to cell density, competition for nutrients, accumulating
waste products, etc. (decrease in slope)
Stationary phase:
- overall population growth plateaus
- Due to a growth-limiting factor such as the depletion of essential nutrient(s), and/or formation of an inhibitory product
- horizontal linear part of the curve
Death phase:
Without any new nutrients (and/or production of toxic byproducts by dying cells), all cells will eventually die off
4. Death phase
The chemostat ensures…
continuous logarithmic growth by constantly adding and removing equal amounts of
culture medium
