Chapter 4: Dynamics of Prokaryotic Growth. Important Point:
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Transcript of Chapter 4: Dynamics of Prokaryotic Growth. Important Point:
Eac
h S
peci
es is
Uni
que Bacteria are incredibly diverse, but...
Each bacterial species can grow in only a limited set of environments.
Each bacterial species can grow only if presented with the right nutrients/conditions.
In addition, bacteria produce characteristic by-products (e.g., waste products).
We can take advantage of these growth characteristics to identify bacteria phenotypically.
To do these identifications we first have to get organisms in Pure Culture.
Unfortunately, only about 1% of microorganisms currently can be grown in pure culture.
Pur
e-C
ultu
re B
asic
s Sterile = completely free of microbes.
Aseptic Technique = procedures that minimize unintentional introduction of microorganisms to media (cultures) or from cultures to surrounding environment.
Solid media is usually employed to obtain pure cultures.
Agar is usually employed to make solid media.
Agar melts at 95°C and solidifies below 45°C.
Colony = pile of cells descended from single cell (or clump of cells).
Petri Dish = container to which agar is added to obtain pure culture.
Agar Plate (plate) = agar-containing petri dish.
Sto
ring
Pur
e C
ultu
res
Stored pure cultures are often called “Stock Cultures”
Stock cultures often are stored as/using: Frozen in glycerol solution Lyophilized = freeze drying On agar slants As stabs
Bin
ary
Fis
sion
This is how most bacteria undergo cell division (how they replicate).
The interval, division to division,
is called the Generation or
Doubling Time.
Note that not all daughter cells fully
separate after division, e.g.
streptococci, etc.
Tem
pera
ture
Ran
ges
Max due to enzyme
denaturation.
Min due to enzyme & membrane
fluidity problems.
Mes
ophi
les
Most human pathogens are mesophiles.
I.e., organisms adapted to growth at body
temperature.
The
rmop
hile
sImportant source of
heat-stable enzymes (e.g., Taq polymerase or
laundry detergent enzymes).
Oxygen Requirements: The Shake Tube
Note maximum growth nearer to surface (where oxygen is
plentiful; this is not shown well in image).
Don’t worry about enzyme names. Just recall “O2 (product)
detoxification”.
Aerotolerant Anaerobe!
Medically Important Examples
Pseudomonas spp. are obligate aerobes.
Enterics such as Escherichia coli are facultative anaerobes
E.g., Clostridium spp. such as C. botulinum.
Ter
ms
for
Nut
rient
Nee
ds Heterotrophs = require organic carbon (e.g.,
glucose).
Autotrophs convert CO2 to organic carbon.
Carbon fixation = conversion of CO2 to organic carbon.
Nitrogen fixation = conversion of N2 to non-gaseous form (i.e., ammonia).
Growth factors = small organic molecules (e.g., vitamins, amino acids) that must be provided for growth (some bacteria require no “exogenous” “growth factors”).
E.g., Neisseria spp. can require 40 growth factors to grow. We would describe such a bacterium as fastidious.
E. coli requires no growth factors. We would describe such a bacterium as non-fastidious.
Energy & Carbon Source Types
“Chemoautotroph” is good enough for
now.“Chemoheterotroph” is good enough for now.
Chemoheterotrophs differ in the number (and types) of organic compounds they can use. Some Pseudomonas species can utilize 80 different compounds. Other bacteria are limited to as little as only a single organic compound type.
Culture Media Types
Note that, confusingly, many media are both selective and differential, e.g., MacConkey agar.
Enrichment Culture
Means of isolating rare organisms with specific
characteristics from heterogeneous
populations.
Direct Microscopic Count
Requires relatively high bacterial densities.
Usually can’t distinguish living cells from dead cells.
Via
ble
Cou
nts:
Pla
te C
ount
sQuantifies number of
cells (CFUs) capable of replicating.
Note the enumeration
of colony-forming units
(CFUs).
Most Probable Number (MPN)
These are gas-filled tubes, an indication of bacterial growth
(fermentation).
Looking for sufficient dilution
that ~half of tubes show growth.
Reciprocal of that dilution
bacterial density.
Most Probable Number (MPN)
Useful particularly when enumerating
organisms that won’t grow on/in
agar media.
Durham tube.
Growth Curve
Time of gearing up for division following change
in culture conditions.
Division at constant rate (exponential).
Death rate = Birth rate.
Constant per-capita death rate (exponential).
Con
tinuo
us C
ultu
re, C
hem
osta
t
Chemostats are a means of keeping
a culture in log phase indefinitely.
Bio
film
s Biofilms are polysaccharide-encased bacterial
communities attached to environmental surfaces.
Biofilms include slippery rocks (in aquatic environments), slime coating sink drains, yuck yucking up what was once your clean toilet bowl, tarter on your teeth, etc.
“It is estimated that 65% of human bacterial infections involve biofilms.”
“Biofilms are particularly troublesome because they protect organisms against harmful chemicals such as disinfectants” and antibiotics.
They can accumulate on non-sterile medical devices kept in contact with patients over relatively long periods, e.g., on catheters.
Cha
pter
6 N
otes
Don’t worry too much about the details of Glycolysis, Cellular Respiration, or Photosynthesis onward.
These topics are covered on pp. 144-151 and pp. 156-163.
Note, however, that we will cover Glycolysis and Cellular Respiration in class at least from the perspectives of the importance of NAD+ regeneration.