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
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
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
3. Bacterial Growth Curve
A) shows the predictable pattern of bacterial 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
3) stationary phase
a) cell death balances out cell reproduction
b) caused by:
i) decreased nutrients
ii) accumulated wastes
iii) increased cell density
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
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
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
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)
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)
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
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)
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
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
F) Sulfur
1) necessary for the production of select amino acids and is vital for tertiary protein
structrue
2) obtained by consuming sulfur-containing organic molecules
3) also found in rock and sediment deposits often as SO4 (sulfate)
G) Micronutrients & Growth factors
1) obtained by consuming molecules containing them
C. Nutritional Classifications of Microbes
1. Energy Source
A) phototrophic
B) chemotrophic
2. Carbon Source
A) autotrophic
B) heterotrophic
3. Energy & Carbon Sources
A) photoautotrophic
1) photosynthetic orgs
2) considered the primary producers
3) ex. cyanobacteria
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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