Bacterial Growth and Nutrition
•
•
•
•
Bacterial nutrition and culture media
Chemical and physical factors affecting growth
The nature of bacterial growth
Methods for measuring population size
http://diverge.hunter.cuny.edu/~weigang/Images/0611_binaryfission_1.jpg
1
Matter and energy
• 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 extract energy from matter
– Living things can’t turn energy into matter
– Living things can use energy to assemble raw materials.
– Bacteria can’t grow on nothing!
2
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.
3
Essentials of Bacterial nutrition
4
• Macronutrients: needed in larger amounts
– Needed in large quantities: CHONPS
• Carbon, hydrogen, oxygen, nitrogen,
phosphorous, and sulfur. H and O are common.
Sources of C, N, P, and S must also be provided.
– Macronutrients needed in smaller amounts:
• Mineral salts such as Ca+2, Fe+3, Mg+2, K+
• Micronutrients = trace elements;
– needed in very tiny amounts; e.g. Zn+2, Mo+2, Mn+2
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
5
Chemical form must be appropriate
• Not all bacteria can use the same things
– Some molecules cannot be transported in
– Enzymes for metabolizing it might not be present
– Chemical may be used, but more expensive
– These differences are used for identification
• Some chemicals are inert or physically
unusable
– Relatively few bacteria (and only bacteria) use N2
– Diamonds, graphite are carbon, but unusable
– P always in the form of phosphate
6
Make it, or eat it?
7
• 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.
8
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.
9
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
10
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!
http://www.kodak.com/global/images/en/health/filmImaging/thermometer.gif
11
Oxygen: friend or foe?
12
• Early atmosphere of Earth had none
– First created by cyanobacteria using photosynthesis
– Oxygen gas rusted iron in Earth’s crust, then
excess 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
13
– 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.
Fe3+ -SOD + O2- → Fe2+ -SOD + O2
Fe2+ -SOD + O2- + 2H+ → Fe 3+ -SOD + H2O2
Relation to Oxygen
14
• 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
15
• 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
16
• 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.
17
Classification of bacteria based on
temperature
18
Terms related to temperature
19
• Special cases:
– Psychrotrophs: bacteria that grow at “normal”
(mesophilic) temperatures (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
20
• 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
21
• 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 desiccation. Fungi best
– Bread, dry rot of wood
– Survival of bacterial endospores.
Miscellaneous conditions
22
• 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.