Microbial Growth

A. Microbial Reproduction1. 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 GrowthC) new cell wall forms between daughter

cellsD) cells separate or may remain attached

forming chains/clusters1) Strepto – chains2) Staphylo – clusters3) Diplo – groups of 24) Tetrads – groups of 45) Sarcina (Packets) – cube-shaped

packets of 8

Microbial Growth

2. Generation TimeA) time necessary to complete binary

fissionB) average is 30-60 minutes

1) ranges from 5-10 min to 10-30 days2) food-borne pathogens take 20-30

min

Microbial Growth

3. Bacterial Growth CurveA) shows the predictable pattern of

bacterial growth

Microbial Growth

B) 5 phases1) lag phase

a) period of slow or no growthb) cells are producing the molecules

necessary for growth2) 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 phasea) cell death balances out cell

reproductionb) caused by:

i) decreased nutrientsii) accumulated wastesiii) increased cell density

Microbial Growth

4) death phasea) cell death outpaces cell reproductionb) caused by depletion of nutrientsc) 99% of viable cells die

5) phase of prolonged declinea) the “fittest” cells can survive on the

nutrients released by dying cellsb) can last for months to years

Microbial Growth

4. Calculating Population SizeA) 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 divisions2) examples

Microbial Growth

B. Microbial Nutrition1. all life requires 3 groups of nutrients

A) macronutrients (major elements) – needed in large quantities1) 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 SourcesA) Carbon

1) necessary for all cell products2) obtained from organic sources or CO2 (inorganic)

Microbial Growth

B) Nitrogen1) 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 sourcesa) 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) Oxygen1) necessary for biomolecule

production and energy-releasing reactions

2) no real limitations on sourcesa) can be obtained from organic sources, inorganic sources, or directly from air (O2)

Microbial Growth

D) Hydrogen1) obtained from any organic source as

well as many inorganic ones2) necessary for:

a) maintaining pHb) forming H bondsc) biomolecule productiond) energy source for redox reactions

Microbial Growth

E) Phosphorous1) necessary for the production of DNA,

RNA, ATP, and phospholipidsa) usually obtained via these sources

2) very scarce in naturea) found primarily as PO4

-3 (phosphate ion) and H3PO4 (hydrogen phosphate) in rocks and ocean mineral deposits

Microbial Growth

F) Sulfur1) necessary for the production of select

amino acids and is vital for tertiary protein structure

2) obtained by consuming sulfur-containing organic molecules

3) also found in rock and sediment deposits often as SO4 (sulfate)

Microbial Growth

G) Micronutrients & Growth factors1) obtained by consuming molecules containing them

C. Nutritional Classifications of Microbes1. Energy Source

A) phototrophicB) chemotrophic

Microbial Growth

2. Carbon SourceA) autotrophicB) heterotrophic

3. Energy & Carbon SourcesA) photoautotrophic

1) photosynthetic orgs2) considered the primary producers3) ex. cyanobacteria

Microbial Growth

B) chemolithoautotrophic1) very unique2) do not require sunlight or organic

moleculesa) ex. methane-producing bacteria (methanogens) – obtain energy by removing electrons from inorganic molecules and using them to bond C & H

Microbial Growth

C) photoheterotrophic1) also very rare2) some can use chemicals as well as light

for energy (facultative)3) ex. purple and green bacteria

D) chemoheterotrophic1) majority of microbes2) obtain C and energy from organic

sources

Microbial Growth3) many carry out cellular (aerobic)

respiration4) 2 categories

a) saprobic – feed on dead organic matteri) considered free-living

b) parasitic – feed on cells/tissue of living host

5) Saprobesa) primary decomposers

Microbial Growth

b) some can carry out phagocytosis and ingest dead matter

c) most cannot phagocytizei) cell walls prevent itii) must release enzymes to digest matter

then absorb the digested particlesiii) 2 classifications of saprobes

(a) obligate saprobes(b) facultative parasites

Microbial Growth6) Parasites

a) range from viruses to wormsb) 3 types

i) ectoparasites – ex. fungal skin infections

ii) endoparasites – ex. parasitic wormsiii) intracellular parasites – ex. viruses

c) pathogen – parasite which usually causes disease or death

d) obligate parasite

Microbial Growth

D. Non-Nutritional Classifications of Microbes1. Temperature

A) all microbes have 3 critical temps1) minimum temperature2) maximum temperature3) optimal temperature

B) Classifications

Microbial Growth

1) Psychrophilica) opt. temp between -5–15oCb) cannot grow above 20oCc) found in frigid ocean waters

2) Psychrotrophica) opt. temp from 20–30oCb) common cause of food spoilagec) found in cool soil and water

Microbial Growth3) Mesophilic

a) accounts for vast majority of medically important microbes

b) opt. temp of 25–45oCi) 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) Thermophilica) opt. temps above 45oC

i) usually 45–70oCb) 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) Hyperthermophilica) opt. temp from 70–110oCb) usually Archaeac) found in hydrothermal vents in the

ocean floori) a newly discovered bacteria can survive up to 130oC

Microbial Growth

2. Gas RequirementsA) Obligate aerobe

1) require O2 to survive

B) Facultative anaerobe1) grow best in presence of O2 but can survive without it

C) Obligate anaerobe1) cannot use or survive in the presence of O2

Microbial Growth

D) Microaerophile1) require small amounts of O2 but

larger amounts will inhibit growthE) Aerotolerant anaerobe

1) cannot use O2 but can survive in its presence

F) Capnophile1) grow best in environments with high

CO2

Microbial Growth

3. pH RequirementsA) Neutrophilic

1) prefer pH of 5–8a) human pathogens usually 6.5–7.5

2) don’t grow well in extremesa) inhibits enzyme function

Microbial Growth

B) Acidophilic1) grow best at pH below 5.52) ex. Helicobacter & Lactobacillus

C) Alkalophilic1) grow best at pH above 8.52) found in alkaline lakes and soils

Microbial Growth4. Osmotic Pressure (Salt Concentration)

A) most microbes prefer isotonic or hypotonic environments

B) 2 main classifications1) Osmotolerant

a) can survive up to 10% NaCl2) Halophilic

a) require at least 9% NaCl but optimal is ~25%

b) ex. Staphylococcus