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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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
1
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, 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
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• Siderophores and hemolysins
– For collecting iron. (e.g. electron transport systems)
• Extracellular enzymes: leave cell, go out into medium,
break down polymers, release LMW compounds.
• Genetic regulation: cell uses other nutrient sources.
• Semi-starvation state: slower metabolism, smaller
size.
• Sporulation: cells form environmentally resistant
resting state. Endospores form within cells; others
become spores.
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.
Culture Medium
• 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.
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Defined Medium for Cytophagas/Flexibacters
Component
K2HPO4
0.10
KH2PO4
0.05
MgCl2
0.36
NaHCO3
0.05
{CaCl2
1 ml*
{BaCl2.2H2O
Na acetate
0.01
FeCl.7H2O
ml*
RNA
0.10
alanine
0.15
arginine
0.20
aspartic acid
glutamic acid
grams
0.2
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 require wide ranges of
conditions
– Optimal conditions implied by “-phile”
meaning “love”
• Some bacteria prefer other
conditions, but can tolerate extremes
– Suffix “-tolerant”
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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
• Aerobes: use oxygen in metabolism; obligate.
• Anaerobes: grow without oxygen
• Microaerophiles: require oxygen, but in small
amounts.
• Capnophiles: require larger amounts of carbon
dioxide.
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Oxygen and microbes continued
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• Classifications vary, but our definitions:
– Obligate anaerobes: killed or inhibited by oxygen.
– Aerotolerant anaerobes: do not use oxygen, but not
killed by it.
– Facultative anaerobes: can 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.