Microbiology Chapter 6 Terms

Front 1

nutrient

Back 1

any chemical required for growth of microbial populations. The most important of these are compounds containing carbon, oxygen, nitrogen, and/or hydrogen.

Front 2

colony

Back 2

an aggregation of cells arising from a single parent cell.

Front 3

All cells require three things to conduct metabolism:

Back 3

a carbon source, a source of energy, and a source of electrons or hydrogen atoms.

Front 4

Organisms can be categorized into one of four groups based on their source of carbon and their use of either chemicals or light as a source of energy. They are:

Back 4

Photoautotrophs, Chemoautotrophs,
Photoheterotrophs,
Chemoheterotrophs

Front 5

Photoautotrophs

Back 5

use carbon dioxide as a carbon source and light energy from the environment to make their own food.

Front 6

Chemoautotrophs

Back 6

use carbon dioxide as a carbon source but catabolize organic molecules for energy.

Front 7

Photoheterotrophs

Back 7

are photosynthetic organisms that acquire energy from light and acquire nutrients via catabolism of organic compounds.

Front 8

Chemoheterotrophs

Back 8

use organic compounds for both energy and carbon.

Front 9

organotrophs

Back 9

acquire electrons from organic sources

Front 10

lithotrophs

Back 10

acquire electrons from inorganic sources

Front 11

Obligate aerobes

Back 11

require oxygen as the final electron acceptor of the electron transport chain

Front 12

obligate anaerobes

Back 12

cannot tolerate oxygen and use an electron acceptor other than oxygen.

Front 13

Toxic forms of oxygen are highly reactive and cause a chain of vigorous oxidation. Four forms of oxygen are toxic are:

Back 13

Singlet oxygen (1O2),
Superoxide radicals (O2–),
Peroxide anion (O22–),
Hydroxyl radicals (OH.)

Front 14

Singlet oxygen (1O2)

Back 14

is molecular oxygen with electrons that have been boosted to a higher energy state, typically during aerobic metabolism.

Front 15

Superoxide radicals (O2–)

Back 15

are formed during the incomplete reduction of oxygen during electron transport in aerobes and during metabolism by anaerobes in the presence of oxygen. They are detoxified by superoxide dismutase.

Front 16

Peroxide anion (O22–)

Back 16

is a component of hydrogen peroxide, which is formed during reactions catalyzed by superoxide dismutase. The enzymes catalase and peroxidase detoxify peroxide anion.

Front 17

Hydroxyl radicals (OH.)

Back 17

result from ionizing radiation and from the incomplete reduction of hydrogen peroxide. Hydroxyl radicals are the most reactive of the four toxic forms of oxygen, but because hydrogen peroxide does not accumulate in aerobic cells, the threat of hydroxyl radicals is virtually eliminated in aerobic cells.

Front 18

carotenoids

Back 18

Phototropic microorganisms often contain pigments that prevent toxicity by removing the excess energy of singlet oxygen.

Front 19

Facultative anaerobes

Back 19

can maintain life via fermentation or anaerobic respiration, though their metabolic efficiency is often reduced in the absence of oxygen.

Front 20

Aerotolerant anaerobes

Back 20

prefer anaerobic conditions, but can tolerate oxygen because they have some form of the enzymes that detoxify oxygen’s poisonous forms.

Front 21

Microaerophiles

Back 21

require low levels of oxygen.

Front 22

Capnophiles

Back 22

grow best with high carbon dioxide levels in addition to low oxygen levels

Front 23

trace elements

Back 23

selenium, zinc, etc., are required.

Front 24

growth factors

Back 24

Most microorganisms also require small amounts of certain organic chemicals that they cannot synthesize. For example, vitamins are growth factors for some microorganisms.

Front 25

In addition to chemical nutrients, organisms have physical requirements for growth, these are:

Back 25

specific conditions of temperature, pH, osmolarity, and pressure.

Front 26

optimum growth temperature.

Back 26

Though microbes survive within the limits imposed by a minimum growth temperature and a maximum growth temperature, an organism’s metabolic activities produce the highest growth rate.

Front 27

Psychrophiles

Back 27

require temperatures below 20°C.

Front 28

Mesophiles

Back 28

grow best at temperatures ranging between about 20°C and 40°C.

Front 29

Thermophiles

Back 29

Thermophiles require temperatures above 45°C.

Front 30

Hyperthermophiles

Back 30

require temperatures above 80°C.

Front 31

neutrophiles

Back 31

Most bacteria and protozoa grow best in a narrow range around a neutral pH, between 6.5 and 7.5.

Front 32

acidophiles

Back 32

other bacteria and many fungi grow best in acidic environments where pH can range as low as 0.0.

Front 33

alkalinophiles

Back 33

live in alkaline soils and water up to pH 11.5.

Front 34

Obligate halophiles

Back 34

require high osmotic pressure such as exists in salt water.

Front 35

Facultative halophiles

Back 35

do not require but can tolerate salty conditions.

Front 36

barophiles.

Back 36

Water exerts pressure in proportion to its depth, and the pressure in deep ocean basins and trenches is tremendous. Organisms that live under extreme pressure Their membranes and enzymes depend on pressure to maintain their three-dimensional functional shapes, and typically they cannot survive at sea level.

Front 37

Relationships in which one organism harms or even kills another are considered

Back 37

antagonistic.

Front 38

synergistic relationships

Back 38

members of an association cooperate such that each receives benefits that exceed those that would result if each lived separately.

Front 39

symbiotic relationships

Back 39

organisms live in close nutritional or physical contact, becoming interdependent.

Front 40

Biofilms

Back 40

an example of complex relationships among numerous individuals, which are often different species, that together attach to surfaces and display metabolic and structural traits different from those expressed by any of the microorganisms alone.

Front 41

quorum sensing

Back 41

a process in which bacteria respond to the density of nearby bacteria by utilizing signal and receptor molecules.

Front 42

inoculum

Back 42

Microbiologists culture microorganisms by transferring —a sample—

Front 43

a medium

Back 43

from a clinical or environmental specimen into, a collection of nutrients.

Front 44

Liquid media are called

Back 44

broths

Front 45

Microorganisms that grow from an inoculum are called a

Back 45

culture

Front 46

clinical specimen

Back 46

is a sample of human material such as feces, saliva, cerebrospinal fluid, or blood, that is examined and tested for the presence of microorganisms. Clinical specimens must be properly labeled and transported to a microbiological laboratory to avoid both death of the pathogens and growth of normal organisms.

Front 47

defined medium (or synthetic medium).

Back 47

A medium for which the precise chemical composition is known

Front 48

Complex media

Back 48

contain a variety of growth factors and can support a wider variety of microorganisms than defined media.

Front 49

Selective media

Back 49

typically contain substances that either favor the growth of particular microorganisms or inhibit the growth of unwanted ones.

Front 50

Differential media

Back 50

are formulated such that either the presence of visible changes in the medium or differences in the appearances of colonies helps microbiologists differentiate among the different kinds of bacteria growing on the medium. One example involves the differences in organisms’ utilization of the red blood cells in blood agar.

Front 51

Reducing media

Back 51

provide conditions conducive to culturing anaerobes. They contain compounds that chemically combine with free oxygen and remove it from the medium.

Front 52

Transport media

Back 52

are used by health care personnel to move specimens safely from one location to another while maintaining the relative abundance of organisms and preventing contamination of the specimen or environment.

Front 53

Animal and cell cultures

Back 53

allow for the growth of microorganisms for which artificial media are inadequate. Mammals, bird eggs, and cultures of living cells are used.

Front 54

Low-oxygen cultures

Back 54

favor the growth of microorganisms that thrive in environments intermediate between strictly aerobic and anaerobic, such as within the respiratory or intestinal tract of mammals. Candle jars, chemical packets, or carbon dioxide incubators are used to remove oxygen from the environment.

Front 55

Enrichment cultures

Back 55

use a selective medium designed to increase very small numbers of a chosen microbe to observable levels.

Front 56

Cold-enrichment cultures

Back 56

require the incubation of a specimen in a refrigerator, allowing for the enrichment of the culture with cold-tolerant species.

Front 57

Lyophilization

Back 57

is freeze drying; that is, removal of water from a frozen culture via an intense vacuum.

Front 58

lag phase

Back 58

the organisms are adjusting to their environment

Front 59

log phase

Back 59

the population is most actively growing

Front 60

stationary phase

Back 60

new organisms are being produced at the same rate at which they are dying.

Front 61

death phase

Back 61

the organisms are dying more quickly than they can be replaced by new organisms.

Front 62

viable plate counts

Back 62

microbiologists base an estimate of the size of a microbial population upon the number of colonies formed when diluted samples are plated onto agar media.

Front 63

membrane filtration

Back 63

a large sample is poured through a filter small enough to trap cells.

Front 64

microscopic counts

Back 64

a sample is placed on a cell counter, a glass slide with an etched grid, and viewed through a microscope. A microbiologist can count the number of bacteria in several of the large squares and then calculate the mean number of bacteria per square.

Front 65

Electronic counters

Back 65

are devices that count cells as they interrupt an electrical current flowing across a narrow tube held in front of an electronic detector. Flow cytometry is one variation.

Front 66

most-probable number (MPN) method

Back 66

is a statistical estimating technique based on the fact that the more bacteria in a sample, the more dilutions are required to reduce their number to zero.

Front 67

Among the indirect methods are: measurements of metabolic activity; measurements of a population’s dry weight; and measurement of the turbidity of a broth, especially by a device known as a

Back 67

spectrophotometer.