Transcript Bacterial Growth and Nutrition

Bacterial Growth and Nutrition
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Bacterial nutrition and culture media
Chemical and physical factors affecting growth
The nature of bacterial growth
Methods for measuring population size
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The First Law of Thermodynamics
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• Energy cannot be created or destroyed.
– It is interchangeable with matter.
– Einstein’s famous equation: E = mc2
• In order to grow, bacteria need a source of raw
materials and energy
– Source can be the same (e.g. glucose) or different
(e.g. carbon dioxide and sunlight).
– Living things can’t turn energy in raw materials, only
use it to assemble raw materials.
– Bacteria can’t grow on nothing!
Where do raw materials come from?
• Bacteria acquire energy from oxidation of organic or
inorganic molecules, or from sunlight.
• Growth requires raw materials: some form of carbon.
• Autotrophs vs. heterotrophs
– Auto=self; hetero=other; troph=feeding.
– Autotrophs use carbon dioxide
– Heterotrophs use pre-formed organic compounds
(molecules made by other living things).
– Humans and medically important bacteria are
heterotrophs.
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Essentials of Bacterial nutrition
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• Six elements needed in large quantities by all living
things: CHONPS
– Carbon, hydrogen, oxygen, nitrogen, phosphorous,
and sulfur. H and O are common. Sources of C, N,
P, and S must also be provided.
• Other macronutrients: not as much needed:
– Mineral salts such as Ca+2, Fe+3, Mg+2, K+
• Micronutrients = trace elements; needed in very tiny
amounts: things like Zn+2, Mo+2, Mn+2
• Elements must be in the correct chemical form!
– Diamonds, graphite no good. N2 used by very few
bacteria.
Element
% dry wgt
Source
Carbon
50
organic compounds or CO2
Oxygen
20
H2O, organic compounds, CO2, and O2
Nitrogen
14
NH3, NO3, organic compounds, N2
Hydrogen
8
H2O, organic compounds, H2
Phosphorus
3
inorganic phosphates (PO4)
Sulfur
1
SO4, H2S, So, organic sulfur
compounds
Potassium
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Potassium salts
Magnesium
0.5
Magnesium salts
Calcium
0.5
Calcium salts
Iron
0.2
Iron salts
http://textbookofbacteriology.net/nutgro.html
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Make it, or eat it?
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• Some bacteria are remarkable, being able to
make all the organic compounds needed from a
single C source like glucose.
• For others:
– Vitamins, amino acids, blood, etc. added to a
culture medium are called growth factors.
– Bacteria that require a medium with various growth
factors or other components and are hard to grow
are referred to as fastidious.
Feast or famine: normal is what’s normal for
you:
Oligotrophs vs. copiotrophs
• Oligo means few; oligotrophs are adapted to life in
environments where nutrients are scarce
– For example, rivers, other clean water systems.
• Copio means abundant, as in “copious”
– The more nutrients, the better.
– Medically important bacteria are copiotrophs.
– Grow rapidly and easily in the lab.
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Responses of microbes to nutritional
deficiency
• Siderophores, hemolysins, and extracellular enzymes
– Collect iron, other nutrients.
• Semi-starvation state: slower metabolism, smaller
size.
• Sporulation and “resting cells”:
– cells have very low metabolic rate
– Some cells change shape, develop thick coat
– Endospores form within cells; very resistant.
– Bacteria form spores for survival
• Fungi form spores for reproduction
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Endospore formation
http://www.microbe.org/art/endospore_cycle.jpg
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Responses of microbes to other
environmental stresses
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• Compatible solutes: small neutral molecules
accumulated in cytoplasm when external environment
is hypertonic.
• Heat shock proteins and other stress proteins
– Bacteria express additional genes that code for
protective proteins.
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Culture Medium
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• Defined vs. Complex
– Defined has known amounts of known chemicals.
– Complex: hydrolysates, extracts, etc.
• Exact chemical composition is not known.
• Selective and differential
– Selective media limits the growth of unwanted
microbes or allows growth of desired ones.
– Differential media enables “differentiation” between
different microbes.
– A medium can be both.
Defined Medium for Cytophagas/Flexibacters
Component
K2HPO4
KH2PO4
MgCl2
NaHCO3
{CaCl2
{BaCl2.2H2O
Na acetate
FeCl.7H2O
RNA
alanine
arginine
aspartic acid
glutamic acid
grams
0.10
0.05
0.36
0.05
1 ml*
0.01
0.2 ml*
0.10
0.15
0.20
0.30
0.55
glycine
histidine
isoleucine
leucine
lysine
phenylalanine
proline
serine
threonine
valine
0.02
0.20
0.30
0.20
0.40
0.30
0.50
0.30
0.50
0.30
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Physical requirements for growth
• Prefixes and suffixes:
• Bacteria are highly diverse in the
types of conditions they can grow in.
– Optimal or required conditions implied by
“-phile” meaning “love”
• Some bacteria prefer other
conditions, but can tolerate extremes
– Suffix “-tolerant”
• Note the difference!
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Oxygen: friend or foe?
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• Early atmosphere of Earth had none
– First created by cyanobacteria using photosynthesis
– Iron everywhere rusted, then collected in
atmosphere
• Strong oxidizing agent
• Reacts with certain organic molecules,
produces free radicals and strong oxidizers :
– Singlet oxygen, H2O2(peroxide), O3- (superoxide),
and hydroxyl (OH-) radical.
Protections of bacteria against oxygen
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– Bacteria possess protective enzymes, catalase and
superoxide dismutase.
– Catalase breaks down hydrogen peroxide into
water and oxygen gas.
– Superoxide dismutase breaks superoxide down into
peroxide and oxygen gas.
– Anaerobes missing one or both; slow or no growth
in the presence of oxygen.
Relation to Oxygen
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• Aerobes: use oxygen in
metabolism; obligate.
A: aerobe
B: microaerophile
• Microaerophiles: require oxygen
(also obligate), but in small
amounts.
• Anaerobes: grow without
oxygen; SEE NEXT
•Capnophiles: require larger amounts of carbon dioxide
than are found normally in air.
Anaerobes grow without O2
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• Classifications vary, but our
definitions:
– Obligate (strict) anaerobes:
killed or inhibited by
oxygen.
– Aerotolerant anaerobes: do
not use oxygen, but not
killed by it.
C: could be facultative
– Facultative anaerobes: can or aerotolerant.
D: strict anaerobe
grow with or without
oxygen
Effect of temperature
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• Low temperature
– Enzymatic reactions too slow; enzymes too stiff
– Lipid membranes no longer fluid
• High temperature
– Enzymes denature, lose shape and stop functioning
– Lipid membranes get too fluid, leak
– DNA denatures
• As temperature increases, reactions and growth
rate speed up; at max, critical enzymes
denature.
Bacteria and temperature
• Bacteria have temperature ranges (grow between 2
temperature extremes), and an optimal growth
temperature. Both are used to classify bacteria.
• As temperature increases, so do metabolic rates.
• At high end of range, critical enzymes begin to
denature, work slower. Growth rate drops off rapidly
with small increase in temperature.
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Classification of bacteria based on
temperature
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Terms related to temperature
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• Special cases:
– Psychrotrophs: bacteria that grow at “normal”
temperature ranges (e.g. room temperature” but
can also grow in the refrigerator; responsible for
food spoilage.
– Thermoduric: more to do with survival than growth;
bacteria that can withstand brief heat treatments.
pH Effects
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• pH = -log[H+]
• Lowest = 0 (very acid); highest = 14 (very
basic) Neutral is pH 7.
• Acidophiles/acidotolerant grow at low pH
• Alkalophiles/alkalotolerant grow at high pH
• Most bacteria prefer a neutral pH
– What is pH of human blood?
• Some bacteria create their preferred conditions
– Lactobacillus creates low pH environment in vagina
Low water activity:
halophiles, osmophiles, and xerotolerant
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• Water is critical for life; remove some, and things can’t
grow. (food preservation: jerky, etc.)
• Halophiles/halotolerant: relationship to high salt.
– Marine bacteria; archaea and really high salt.
• Osmophiles: can stand hypertonic environments
whether salt, sugar, or other dissolved solutes
– Fungi very good at this; grandma’s wax over jelly.
• Xerotolerant: dry. Subject to dessication. Fungi best
– Bread, dry rot of wood
– Survival of bacterial endospores.
Miscellaneous conditions
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• Radiation (solar, UV, gamma)
– Can all damage cells; bacteria have pigments to
absorb energy and protect themselves.
– Endospores are radiation resistant.
– Deinococcus radiodurans: extremely radiation
resistant
• Extremely efficient DNA repair, protection against
dessication damage to DNA.
• Barophiles/barotolerant: microbes from deep sea
– Baro- means pressure. Actually require high
pressure as found in their environment.