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15 C; polar regions; extremely cold


20-30C; spoilage of refrigerated foods


about 37C; most pathogens and spoilage organisms; most common microbes


compost piles, spoilage of canned goods, optimum is 80 C or higher


hydrothermal vents, hot springs; extremely hot, optimum is 80C or higher

molds and yeasts can grow

5-6 pH

most bacteria can grow

6.5-7.5 pH

osmotic pressure

a physical growth requirement; can have the effect of removing water from a cell


shrinkage of the cell's cytoplasm


necessary for structural organic molecules, energy source


necessary in amino acids, proteins, and nucleic acids; most bacteria decompose proteins (NH4+ or NH3-), N2 in nitrogen fixation


necessary in amino acids (cys, met), thiamine and biotin (vitamins); use SO4(2-) or H2S to decompose proteins


necessary in DNA, RNA, ATP, and membranes (phospholipids); PO4(3-)

trace elements

necessary inorganic elements required in small amounts usually as enzyme cofactors
EX- zinc, iron, magnesium

obligate aerobes

require O2 to grow, grow at top of tube

facultative anaerobes

grow better with O2, but can grow without it; don't have SOD (superoxide dismutase) so can't make catalase or peroxides

aerotolerant anaerobes

fermenters, don't care about O2-irrelevant; grow dispersed


need some O2; grow in the middle of tube

superoxide dismutase (SOD)

enzyme that can neutralize the superoxide free radicals (O2-) which are very toxic to the cell, without this, you can not get rid of O2-


converts hydrogen peroxide to water and oxygen (why hydrogen peroxide bubbles on a wound), human tissues contain this


enzyme that breaks down hydrogen peroxide but differs from catalase in that its reaction does not produce oxygen

chemically defined media

EXACT chemical composition is known

complex media

extracts and digests of yeasts, meat, or plants (nutrient broth, nutrient agar)

reducing media

used in the cultivation of anaerobic bacteria because otherwise, anaerobes might be killed by exposure; contain chemicals (thioglycollate or oxyrase) that chemically combine with dissolved oxygen and deplete the oxygen in the culture medium

selective media

suppresses unwanted microbes and encourages growth of desired microbes

differential media

makes it easy to distinguish colonies of different microbes from each other
EX- blood agar


complex polysaccharides used as solidifying agent for culture media
EX- Petri plates, slants, and deeps


a population of cells arising from a single cell or spore (or from a group of attached cells); often called a colony-forming unit (CFU)

binary fission

the normal reproductive method of bacteria, in which a single cell divides into two identical cells

generation time

the time it takes a cell to divide (or population to double)

lag phase

intense metabolic activity preparing for population growth, but no increase in population; "set-up"

log phase

logarithmic, or exponential, increase in population; cellular reproduction (division) most active, cells are most active metabolically

stationary phase

period of equilibrium; microbial death is balanced with the production of new cells; nutrients deplete

death phase

population is decreasing at a logarithmic rate; cell death exceeds number of new cells formed

plate count

colony counting method: perform dilutions of a sample, inoculate Petri plates from serial dilutions, and after incubation, count colonies on plates that have 25-250 colonies (CFUs)


colony counting method: bacteria are retained on the surface of a membrane filter and then transferred to a culture medium to grow and subsequently be counted

direct microscopic count

colony counting method: the microbes in a measured volume of a bacterial suspension are counted with the use of a specially designed slide


as bacteria multiply in a liquid medium, the medium becomes turbid or cloudy with cells


used to measure the turbidity by measuring the amount of light that passes through a suspension of cells; less light transmitted = the more bacterial suspension, counts both the live and dead cells

plate count formula

cells/ml= N/ D X V
N= number of colonies
D= dilution


grow in acidic environments, below a 5 pH generally

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