Effect of Environmental Factors on Growth
1. Water
Availability
2. pH
3. Temperature
4. Oxygen
level
1. Water Availability
Water availability depends on
ï
water content of an environment
ï the concentration
of solutes in the environment
measured as water
activity, aw
ratio:
vapor pressure of air in equilibrium with
a solute
vapor pressure of air in equilibrium with
pure water
Pure water = 1.
osmotic effects
High salt/high sugar solutions are analogous to
a dry environment.
A halophile
can tolerate some salt.
A halotolerant
organism tolerates a range of conditions
An extreme
halophile can grow in extremely salty conditions:
An osmophile can grow in high sugar.
2. pH
Acidophiles- pH
between 0 and 5.5
Neutrophiles- pH
between 5.5 and 8
Alkalophiles- pH
between 8.5 and 11.5 (Extreme,
> 10)
Internal pH is kept pretty neutral!
Changes in pH: disrupt membranes, also
denature enzymes.
3. Temperature
A microorganism's temperature varies with the
temperature of the environment
enzyme
reaction rates (low)
denaturing
of enzymes and nucleic acids (high)
Psychrophiles: optimal growth temperature <15ƒ C
Psychrotolerant: 20-40ƒ
C, tolerate broad range including low temperatures
Mesophiles: optima
around 20-40ƒ
Thermophiles (> 40ƒ
C) and hyperthermophiles (>80ƒC)
No eukaryotic hyperthermophiles... (none
above 60ƒ)
Archaea: often adapted to extreme
habitats, and extreme combinations- e.g. acid or alkaline hot springs
Biotechnological applications of
extremophiles:
ï living organisms are the most efficient way
to synthesize complex compounds such as enzymes, and perform most chemical
reactions!!
ï enzymes of thermophiles especially useful:
more stable than enzymes from mesophiles, and also many industrial and
biotechnological processes will run more efficiently at high temperatures.
Aerobes vs. anaerobes: Can/can't
grow in the presence of atmospheric O2.
Aerobes: oxygen serves as the terminal electron acceptor in
aerobic respiration.
Obligate: required.
Obligate
aerobe, obligate anaerobe
Facultative: can grow that way (but better the other way)
E.
coli is a facultative anaerobe. Note some texts define this word the
opposite way! E. coli is a
facultative aerobe
Aerotolerant anaerobe: ignores
the air.
Strict or obligate: required.
Bacteroides is an obligate anaerobe.
Oxygen produces poisonous compounds-
Evolution of life: life evolved in an anoxic atmosphere (~4 billion years
ago). Evolution of microorganisms that could extract oxygen from water in a
light-driven reaction for the reduction of carbon dioxide!
Photosynthesis: a sharp rise in atmospheric
oxygen, 2 to 1.8 billion years ago
Result: a need to for cells to protect
themselves from oxygen.
Two strategies: hide, or use enzymes to break
down the toxic products of oxygen:
superoxide
dismutase
catalase
Control of Microorganisms by Physical and Chemical Means
Sterilization:
kill or remove all
living cells, spores, viruses on an object of habitat.
Disinfection:
kill, inhibit, or
remove disease-causing microorganisms.
Sanitization:
reduce
the microbial population to safe levels.
Antisepsis:
prevent infection
or sepsis, with an antiseptic
germicide
bactericide
fungicide
algaecide
viricide.......
When is a microbe dead?
If it doesn't grow when you put it into a good culture
medium...
Microbial death is usually exponential or
logarithmic.
Not all the microbes are killed at once!
What affects the efficiency
of an antimicrobial agent?
1. population size
2. composition of the population
(species, endospores)
3. concentration of the agent
4. duration of exposure
5. temperature
6. local environment (for example, acidity;
organic matter)
HEAT
ï boiling
doesn't
kill endospores
TDP = thermal death point, the lowest
temperature at which a microorganism is killed in 10 minutes
TDT = thermal death time, shortest time
needed to kill a microorganism under specified conditions
D = decimal reduction time, the time needed
to kill 90% of the microorganisms or spores under specified heat
AUTOCLAVING
ï combines heat, moisture and pressure
PASTEURIZATION
Controlled heating, kills certain
microorganisms.
DRY HEAT (BAKING)
useful for equipment, glassware, etc.
FILTRATION
get rid of the microbes directly! good for
heat-sensitive things, like antibiotics, pharmaceuticals. Air (safety hoods)!
RADIATION
UV (260 nm- doesn't penetrate, so surfaces
only),
ionizing- gamma. Used for cold sterilization
- plasticware
CHEMICAL AGENTS
Phenolics
used in hospitals- Lysol types
Alcohols
don't kill spores. Thermometers
Halogens
chlorine in water systems
Heavy Metals
silver
nitrate in babies' eyes; mercury. Toxic!
Detergents
(quaternary ammonium compounds)
skin
Aldehydes
formaldehyde, glutaraldehyde
Gases
ethylene oxide gas- used for plasticware Petri dishes,
penetrates!
ANTIBIOTICS AND GROWTH FACTOR ANALOGS
Agents that can be used inside the body:
"Chemotherapeutic agents"
Required by an
organism, because the organism canít synthesize them.
Growth factor
analogs: chemically related to
(mimic) growth factors, and block uptake or utilization of growth factors. They
are not naturally-produced substances.
ï Antibiotics are naturally produced by
bacteria and fungi.
ï Naturally-produced antibiotics have been
used as the basis for the design of novel, "semisynthetic"
antibiotics.
ï Over 10,000 have been discovered, but only
~100 in commercial production
ï Actinomycetes (division of the G+ bacteria)
ï Range of action:
Broad
spectrum: Targets Gram+, Gram-. Or may target Mycobacteria and G-, or G+ and
intracellular (parasitic) bacteria
Examples:
Cephalosporins (G+ and G-), Tetracycline (G+, G-, intracellular bacteria)
Note
that no antibiotics target viruses.
Narrow
spectrum: target a specific group, such as G+, or even one species. Examples
Polymyxins (G+)
ï Major modes of action:
50S:
Erythromycin, chloramphenicol
30S:
Tetracyclines, streptomycin
EXAMPLES OF IMPORTANT ANTIBIOTIC GROUPS:
Mechanisms of action:
Bacterial cell walls: glycan-linked peptide
chains, linked by the transpeptidation reaction, carried out by transpeptidase enzymes. Transpeptidase enzymes also bind antibiotics
with the b-Lactam ring, and when bound, can no longer catalyze
the transpeptidase reaction. Result: weakened, eventually degraded cell walls.
Penicillin G is active against G+ bacteria
Tetracyclines
ï Produced by bacteria
ï First broad-spectrum antibiotics
Mode of Action:
Protein synthesis inhibitor- interferes with
30S ribosomal subunit function