Microbiology Ch 6 - Microbial Growth

Microbial Growth

an increase in number of cells, not cell size

discrete colony

an aggregation of cells arising from a single parent cell


what results in growth?

nutrients: chemical and energy requirements

1) Source of Carbon, Energy, and Electrons 2) Oxygen Requirements 3) Nitrogen Requirements 4) Other chemical requirements


those using an inorganic source of carbon (Carbon dioxide)


those catabolizing reduced organic molecules (proteins, carbohydrates, amino acids, and fatty acids)


those that acquire energy from Redox reactions involving Inorganic and Organic chemicals


those that use light as their energy source

Obligate Aerobes

must have oxygen to survive

Obligate Anaerobes

poisoned by oxygen and cannot tolerate it

Singlet Oxygen

molecular oxygen with electrons boosted to higher energy state (usually during Aerobic Metabolism)


Phototrophic organisms have these to remove the excess energy of Singlet Oxygen

Superoxide free radicals

some form during incomplete reduction of Oxygen, during Electron Transport in Aerobes ,and during metabolism by Anaerobes in presence of Oxygen

Peroxide Anion

formed during reactions catalyzed by Superoxide Dismutase and other reaction

Hydroxyl radical

results from ionizing radiation and from incomplete reduction of Hydrogen Peroxide

Hydroxyl radical

The most reactive of the four toxic forms of oxygen

Hydroxyl radical

Not a threat to Aerobes due to actions of the enzymes Catalase and Peroxidase which prevent H2O2 from accumulating


undergo Aerobic Respiration


do not use Aerobic Metabolism

Facultative Anaerobes

can maintain life via Fermentation or Anaerobic Respiration or by Aerobic respiration

Aerotolerant Anaerobes

do not use Aerobic Metabolism, but do have some enzymes that detoxify oxygen's poisonous forms, so can grow in its presence


Aerobes that require Oxygen levels from 2-10% and have a limited ability to detoxify Hydrogen Peroxide and Superoxide Radicals

Trace Elements

inorganic elements required in small amounts, usually enzyme cofactors

Growth Factors

organic chemicals that cannot be synthesized by certain organisms (Vitamins, Essential Amino Acids, Purines, Pyrimidines, Cholesterol, NADH, and Heme)

Temperature, pH, Osmotic Pressure

Physical requirements for growth

effect of temperature on proteins

can denature them at high temp.

effect of low temperature on lipid-containing membranes of cells and organelles

makes them rigid and fragile

effect of high temperature on lipid-containing membranes of cells and organelles

makes them too fluid and they cannot contain the cell or organelle any longer

optimum growth temperature

that at which growth rate is highest

categories of microbes based on temperature range

psychrophiles, mesophiles, thermophiles, and hyperthermophiles


grow best at about 15 degrees celcius; can grow below 0 degrees celcius, but not much above 20 degrees celcius, cause food spoilage


those growing best between 20 degrees and 40 degrees celcius; the human pathogens are in this group


those that grow above 45 degrees celcius; occur in hot springs and compost piles


Archaea growing about 80 degrees celcius and some above 100 degrees celcius

why organisms are sensitive to changes in acidity

because H+ and OH- interfere with H bonding in proteins and nucleic acids


microbes that grow best in a narrow range around neutral pH (6.5-7.5); includes most bacteria an protozoa


those that grow best in acidic habitats; include other bacteria and fungi


microbes that live in alkaline soils and water up to pH 11.5

why microbes require water

to dissolve enzymes and nutrients require in metabolism; also because it is an important reactant in many metabolic reactions

endospores and cysts

what cease most metabolic activity in a dry environment for years?

hypotonic solutions

those with lower solute concentrations and higher water concentrations; cells placed in these solutions gain water; and if they lack a cell wall, may burst

hypertonic solutions

those with higher solute concentrations and lower water concentrations; cells placed in these solutions undergo CRENATION


shriveling of cytoplasm; this effect helps preserve some foods

obligate halophiles

those that grow in up to 30% salt, require high osmotic pressure

facultative halophiles

those that do not require, but can tolerate high salt concentrations, tolerate high osmotic pressure


organisms that live under extreme pressure


microbial communities that form slime or hydrogels; organized, coordinated, functional community

Quorum Sensing

cell to cell chemical communication


sample of a microbe that is introduced into a Medium


collection of nutrients that may be liquid (broth) or solid (usually agar)

Environmental, Clinical, Stored

the three types of specimens from which the inoculum comes


act of cultivating microorganisms, or the microorganisms that are cultivated

Pure Cultures

contains only 1 species or strain

colony forming unit

a colony (CFU)

Aseptic technique

used to prevent contamination of sterile substances or objects

Streak Plates

isolation technique using a sterile loop or needle to spread inoculum across surface of solid medium to isolate CFUs, to isolate a pure culture

Pour Plates

isolation technique using a series of serial dilutions to separate CFUs, mixed with liquid agar which then solidifies

reducing media

contain ingredients that chemically combine with O2 and are heated to kill off O2, growth of obligate anaerobes

chemically Defined Media

those in which the exact chemical composition is known

Complex Media

nutrients including extracts from yeasts, meat, or plants

Selective Media

suppress growth of unwanted bacteria and encourage growth of desired microbes

Differential Media

make it easier to distinguse colonies of desired microbes from other colonies growing on the plate.

enrichment culture

designed to increase numbers of desired microbes at detectable levels


reproduction process where a small initial outgrowth enlarges until its size approaches that of parent cell


used for short-term storage


used for long-term storage; maintaining temperatures between -50 degrees celcius and -95 degrees celcius


used for very long-term storage; freeze-drying- removing water from frozen culture using intense vacuum converting ice directly into a gas

Binary Fission

reproduction process in which a cell replicated its DNA, grows to twice its normal size, then divides in half, forming two new cells; with each division, the number of cels doubles, increasing by multiples of two

Generation time

time required for cell to grow and divide, population doubles

Growth Curve

graph of the number of organisms in growing population over time

Lag phase

time interval in which cells are very metabolically active (synthesizing enzymes), but not dividing; cell # is constant

Log Phase

time interval in which cells are rapidly growing and reproducing; population increases logarithmically; also when they're most susceptible to drugs

Stationary phase

interval when population is relatively constant, since # of new cells produced = # dying; population stabalizes, equilibrium

Death Phase

interval in which # of dying cells exceeds # of new cells formed; so there is a decline in overall # of cells

Viable Plate Counts

direct method of measuring microbial growth that determines the # of microbes in sampling by counting the # of colonies growing on the agar plate after being serially diluted and transferred to a plate either by spread method or pour plate method; count t


direct method for measuring microbial growth where the number of microbes in a liquid sample is determined by trapping organisms on a fine membrane filter; transferring it to solid culture medium, allowing colonies to grow and counting them

pH of bacteria

pH of 6.5 to 7.5

pH of molds and yeasts

pH of 5 to 6


hypertonic environment, increase in salt or sugar


use organic carbon sources


use CO2


in DNA, RNA, ATP and membranes


in amino acids


in amino acids and proteins


structural organic molecule, energy source


no living microbes


complex polysaccharide, liquifies at 100 celcius, solidifies at 40 celcius.


require high CO2 conditions

biosafety level 1

no special precautions

biosafety level 2

lab coat, gloves, eye protection

biosafety level 3

biosafety cabinets to prevent airborne transmission

biosafety level 4

sealed negative pressure, exhaust air filtered twice


a population of cells arising from a single cell or spore or from a group of attached cells

serial dilutions

original inoculum is diluted several times to ensure colony counts within range

spread plate method

inoculum spread on agar plate and spread uniformly with glass rod


as bacteria multipy within a medium, the medium becomes cloudy with cells, measure with a spectrophotometer.