Acidophile

an organism that grows best at low

pH; typically below pH 5.5

Aerobe

an organism that can use oxygen (O2)

in respiration; some require O2

Aerotolerant anaerobe

a microorganism

unable to respire O2 but whose growth is

unaffected by oxygen

Alkaliphile

an organism that has a growth pH

optimum of 8 or higher

Anaerobe

an organism that cannot use O2 in

respiration and whose growth is typically

inhibited by O2

Batch culture

a closed-system microbial culture

of fixed volume

Binary fission

cell division following

enlargement of a cell to twice its minimum

size

Biofilm

an attached polysaccharide matrix containing

bacterial cells

Cardinal temperatures

the minimum, maximum,

and optimum growth temperatures for

a given organism

Chemostat

a device that allows for the continuous

culture of microorganisms with independent

control of both growth rate and cell number

Compatible solute

a molecule that is accumulated

in the cytoplasm of a cell for adjustment

of water activity but that does not inhibit biochemical

processes

Divisome

a complex of proteins that directs cell

division processes in prokaryotes

Exponential growth

growth of a microbial

population in which cell numbers double

within a specific time interval

Extreme halophile

a microorganism that

requires very large amounts of salt (NaCl),

usually greater than 10% and in some cases

near to saturation, for growth

Extremophile

an organism that grows optimally

under one or more chemical or physical

extremes, such as high or low temperature

or pH

Facultative

with respect to O2, an organism that

can grow in either its presence or absence

FtsZ

a protein that forms a ring along the midcell

division plane to initiate cell division

Generation time

the time required for a population

of microbial cells to double

Growth

an increase in cell number

Halophile

a microorganism that requires NaCl

for growth

Halotolerant

a microorganism that does not

require NaCl for growth but can grow in the

presence of NaCl, in some cases, substantial

levels of NaCl

Hyperthermophile

a prokaryote that has a

growth temperature optimum of 80 C or

greater

an organism that grows best at temperatures

between 20 and 45 C

Microaerophile

an aerobic organism that can

grow only when O2 tensions are reduced

from that present in air

Neutrophile

an organism that grows best at

neutral pH, between pH 5.5 and 8

Obligate anaerobe

an organism that cannot

grow in the presence of O2

Osmophile

an organism that grows best in the

presence of high levels of solute, typically a

sugar

pH

the negative logarithm of the hydrogen ion

(H+) concentration of a solution

Psychrophile

an organism with a growth

temperature optimum of 15 C or lower

and a maximum growth temperature below

20 C

Plate count

a viable counting method where

the number of colonies on a plate is used as a

measure of cell numbers

Psychrotolerant

capable of growing at low

temperatures but having an optimum above

20 C

Thermophile

an organism whose growth temperature

optimum lies between 45 and 80 C

formation of peptide crosslinks

between muramic acid residues in peptidoglycan

synthesis

Viable

capable of reproducing

Water activity

the ratio of the vapor pressure

of air in equilibrium with a solution to that of

pure water

Xerophile

an organism that is able to live, or

that lives best, in very dry environments