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Microbial Growth
A. Microbial Reproduction
1. binary (transverse) fission
A) parent cell enlarges and
duplicates all its genetic material
B) DNA copies move to opposite
ends of parent and attach to a
section of the cell membrane as it
begins to pinch together at the
center
Microbial Growth
C) new cell wall forms between daughter
cells
D) cells separate or may remain attached
forming chains/clusters
1) Strepto – chains
2) Staphylo – clusters
3) Diplo – groups of 2
4) Tetrads – groups of 4
5) Sarcina (Packets) – cube-shaped
packets of 8
Microbial Growth
2. Generation Time
A) time necessary to complete binary
fission
B) average is 30-60 minutes
1) ranges from 5-10 min to 10-30 days
2) food-borne pathogens take 20-30
min
Microbial Growth
3. Bacterial Growth Curve
A) shows the predictable pattern of
bacterial growth
Microbial Growth
B) 5 phases
1) lag phase
a) period of slow or no growth
b) cells are producing the molecules
necessary for growth
2) log (exponential) phase
a) period of optimal growth and
reproduction
b) will continue as long as there are
sufficient nutrients and space
Microbial Growth
3) stationary phase
a) cell death balances out cell
reproduction
b) caused by:
i) decreased nutrients
ii) accumulated wastes
iii) increased cell density
Microbial Growth
4) death phase
a) cell death outpaces cell reproduction
b) caused by depletion of nutrients
c) 99% of viable cells die
5) phase of prolonged decline
a) the “fittest” cells can survive on the
nutrients released by dying cells
b) can last for months to years
Microbial Growth
4. Calculating Population Size
A) population growth is exponential
1) 2  4  8  16  32  64  128…
B) population size can be calculated
1) Nt = (No)2n
a) Nt = final number of cells
b) No = original number of cells
c) n = number of divisions
2) examples
Microbial Growth
B. Microbial Nutrition
1. all life requires 3 groups of nutrients
A) macronutrients (major elements)
– needed in large quantities
1) includes S, C, H, N, O, P
B) micronutrients (trace elements) –
needed in small quantities
1) includes Co, Zn, Cu, Mn, K, Ca,
Na, Mg, and Fe
Microbial Growth
C) essential nutrients (growth factors)
– small organic molecules that cannot
be produced by the cell
2. Nutrient Sources
A) Carbon
1) necessary for all cell products
2) obtained from organic sources or
CO2 (inorganic)
Microbial Growth
B) Nitrogen
1) necessary for the production of
DNA, RNA, ATP, and amino acids
2) most bacteria obtain N by
consuming DNA, RNA, ATP, and
amino acids
3) some obtain N from inorganic
sources
a) NO3- (nitrate), NO2- (nitrite) &
NH3 (ammonia)
Microbial Growth
4) a select few bacteria can obtain N
from air (N2)
a) they must convert it to NH3 (N
fixation) before it can be used
Microbial Growth
C) Oxygen
1) necessary for biomolecule
production and energy-releasing
reactions
2) no real limitations on sources
a) can be obtained from organic
sources, inorganic sources, or
directly from air (O2)
Microbial Growth
D) Hydrogen
1) obtained from any organic source as
well as many inorganic ones
2) necessary for:
a) maintaining pH
b) forming H bonds
c) biomolecule production
d) energy source for redox reactions
Microbial Growth
E) Phosphorous
1) necessary for the production of DNA,
RNA, ATP, and phospholipids
a) usually obtained via these sources
2) very scarce in nature
a) found primarily as PO4-3 (phosphate
ion) and H3PO4 (hydrogen phosphate)
in rocks and ocean mineral deposits
Microbial Growth
F) Sulfur
1) necessary for the production of select
amino acids and is vital for tertiary
protein structure
2) obtained by consuming sulfurcontaining organic molecules
3) also found in rock and sediment
deposits often as SO4 (sulfate)
Microbial Growth
G) Micronutrients & Growth factors
1) obtained by consuming
molecules containing them
C. Nutritional Classifications of Microbes
1. Energy Source
A) phototrophic
B) chemotrophic
Microbial Growth
2. Carbon Source
A) autotrophic
B) heterotrophic
3. Energy & Carbon Sources
A) photoautotrophic
1) photosynthetic orgs
2) considered the primary producers
3) ex. cyanobacteria
Microbial Growth
B) chemolithoautotrophic
1) very unique
2) do not require sunlight or organic
molecules
a) ex. methane-producing bacteria
(methanogens) – obtain energy by
removing electrons from inorganic
molecules and using them to bond
C&H
Microbial Growth
C) photoheterotrophic
1) also very rare
2) some can use chemicals as well as
light for energy (facultative)
3) ex. purple and green bacteria
D) chemoheterotrophic
1) majority of microbes
2) obtain C and energy from organic
sources
Microbial Growth
3) many carry out cellular (aerobic)
respiration
4) 2 categories
a) saprobic – feed on dead organic matter
i) considered free-living
b) parasitic – feed on cells/tissue of living
host
5) Saprobes
a) primary decomposers
Microbial Growth
b) some can carry out phagocytosis and
ingest dead matter
c) most cannot phagocytize
i) cell walls prevent it
ii) must release enzymes to digest matter
then absorb the digested particles
iii) 2 classifications of saprobes
(a) obligate saprobes
(b) facultative parasites
Microbial Growth
6) Parasites
a) range from viruses to worms
b) 3 types
i) ectoparasites – ex. fungal skin
infections
ii) endoparasites – ex. parasitic worms
iii) intracellular parasites – ex. viruses
c) pathogen – parasite which usually
causes disease or death
d) obligate parasite
Microbial Growth
D. Non-Nutritional Classifications of
Microbes
1. Temperature
A) all microbes have 3 critical temps
1) minimum temperature
2) maximum temperature
3) optimal temperature
B) Classifications
Microbial Growth
1) Psychrophilic
a) opt. temp between -5–15oC
b) cannot grow above 20oC
c) found in frigid ocean waters
2) Psychrotrophic
a) opt. temp from 20–30oC
b) common cause of food spoilage
c) found in cool soil and water
Microbial Growth
3) Mesophilic
a) accounts for vast majority of
medically important microbes
b) opt. temp of 25–45oC
i) human pathogens usually 35–40oC
c) found in soil, water, plants and
animals
d) some can withstand short periods of
higher temp = thermoduric
Microbial Growth
4) Thermophilic
a) opt. temps above 45oC
i) usually 45–70oC
b) some can survive up to 100oC
i) temp at which most enzymes are
destroyed
c) found in hot springs, compost heaps
and water heaters
Microbial Growth
5) Hyperthermophilic
a) opt. temp from 70–110oC
b) usually Archaea
c) found in hydrothermal vents in the
ocean floor
i) a newly discovered bacteria can
survive up to 130oC
Microbial Growth
2. Gas Requirements
A) Obligate aerobe
1) require O2 to survive
B) Facultative anaerobe
1) grow best in presence of O2 but
can survive without it
C) Obligate anaerobe
1) cannot use or survive in the
presence of O2
Microbial Growth
D) Microaerophile
1) require small amounts of O2 but
larger amounts will inhibit growth
E) Aerotolerant anaerobe
1) cannot use O2 but can survive in its
presence
F) Capnophile
1) grow best in environments with high
CO2
Microbial Growth
3. pH Requirements
A) Neutrophilic
1) prefer pH of 5–8
a) human pathogens usually 6.5–
7.5
2) don’t grow well in extremes
a) inhibits enzyme function
Microbial Growth
B) Acidophilic
1) grow best at pH below 5.5
2) ex. Helicobacter & Lactobacillus
C) Alkalophilic
1) grow best at pH above 8.5
2) found in alkaline lakes and soils
Microbial Growth
4. Osmotic Pressure (Salt Concentration)
A) most microbes prefer isotonic or
hypotonic environments
B) 2 main classifications
1) Osmotolerant
a) can survive up to 10% NaCl
2) Halophilic
a) require at least 9% NaCl but
optimal is ~25%
b) ex. Staphylococcus