chap 2

Question 1

Bacteria reproduce by

Answer 1

binary fission which involves the separation of a single cell into two more or less identical daughter cells, each containing, among other things, at least one copy of the parental DNA or by budding

Question 2

The lag phase: phase 1

Answer 2

It is characterized by no increase in cell number, but the cells are actively metabolizing in preparation for cell division
It can last from one hour to several days
Enzymes and intermediates are formed and accumulate until they are present in concentrations that permit growth to resume
This phase depends on a wide variety of factors including:
-The time required for synthesis of division factors like enzymes & coenzymes
-The growth medium so that’s why it can be either short or very long

Question 3

Exponential (log) phase: 2nd phase

Answer 3

It’s a pattern of balanced growth wherein all the cells are dividing by binary fission and are growing by geometric progression
The cells divide at a constant rate depending on the composition of the growth medium, the organism itself, and the condition of incubation (Tº, pH, etc..)
The rate of exponential growth of bacterial culture is expressed as generation timealso the doubling timeof the bacterial population
The fastest growing bacteria have generation times of 10-20 minutes under optimum growth conditions, others have of hours or even days.

Question 4

c-Stationary Phase third phase

Answer 4

The growth rates slow the number of death cells balances the number of new cells & the population stabilizes
The metabolism slows down; the living cells maintain a slow metabolic activity
What are the factors that let the cells to enter this phase?
Environmental changes like:
-high cell density,
-exhaustion of nutrients,
-accumulation of waste products, pH changes, …

Question 5

d-Death phase (Final Phase)

Answer 5

Physiological point at which cell deaths exceeds cell births, viable count declines
The cells quickly lose the ability to divide even if they are placed in fresh medium
The death rate increases
A small number of survivors may persist for months or even years
Like the log phase the death phase is so fast and exponential
The death phaseas all phases, can be slowed by lowering the temperature.
So to maintain maximum cell viability it’s best to grow bacterial cultures only to early stationary phase & then chill the culture

Question 6

Bacterial growth over time can be graphed as cell number versus time : Growth Curve
The curve has 4 different phases:

Answer 6

lag phase-exponential (log) phase, stationary phase and death or decline phase.

Question 7

requirements for microbial growth can be divided into two main categories:
a-Physical:

Answer 7

Temperature, pH, Osmotic Pressure & water activity

Question 8

requirements for microbial growth can be divided into two main categories: b-Chemical:

Answer 8

Sources of carbon, nitrogen, Sulfur, phosphorus, trace elements, oxygen & organic growth factors

Question 9

MO are classified into 3 primary groups according to the basis of their preferred range of T:

Answer 9

a-Psycrophiles:
b-Mesophiles:
c-Thermophiles:

Question 10

a-Psycrophiles:

Answer 10

cold loving microbes
- MO can grow slowly @ low temperatures (0-15°C)
but they have their optimum growth T between 15°C-20°Ci

Question 11

b-Mesophiles:

Answer 11

moderate temperature loving

Question 12

c-Thermophiles:

Answer 12

heat loving microbes

Question 13

Ci-Obligate psychrophiles:

Answer 13

• Can grow at 0°C
• Optimum growth 15°C
• Found mostly in deep oceans or in certain polar regions
• Rarely cause problems in food preservation

Question 14

ii-Facultative psychrophiles

Answer 14

• Can grow at 0°C
• Optimum growth T 20°C-30°C
• Responsible for food spoilage

Question 15

Psychrotrophs=

Answer 15

moderate psychrophiles

Question 16

MesophilesModerate-temperature loving microbes

Answer 16

They grow @ ambient temperature
Optimum growth @ 25ºC-40ºC
Include most common type of microorganisms
Include most of the common spoilage and disease organisms (the optimum T for many pathogenic bacteria is about 37°C)

Question 17

Thermophiles

Answer 17

Heat loving or high temperature adapted microbes
Capable of growth at high temperatures
Optimum growth temperature 50ºC-60ºC

Question 18

Hyperthermophiles:

Answer 18

• Optimum growth temperature > 80◦C

Hot springs associated with volcanic activity

Question 19

The pH of an environment affects bacterial growth

Most bacteria grow best between

Answer 19

6-8
In general, bacteria survive alkaline pH better than the acid pH;this is why number of foods like pickles and many cheeses are preserved from spoilage by acids produced by bacterial fermentation

Question 20

Acidophiles

Answer 20

Optimum pH = 1-5.5
Include many fungi and some bacteria
Acids produced by bacterial fermentation used to preserve food: pickles, cheese

Question 21

*Neutrophiles:

Answer 21

*prefer a pH in the range of 5.5 –8(most organisms fall in this category)

Question 22

Alkalophiles:

Answer 22

pH= 8-8.5 to 11
Found in highly basic soda lakes and high carbonate soils
Alkalinity is rarely used to preserve food

Question 23

Plasmolysis:

Answer 23

Interfere with growth
Highly osmotic environments prevent bacterial growth
Addition of sugars, salts can be used to preserve food: jellies, jams, salting of meat

Question 24

In high solute environments, the water is bound to solutes and cannot interact with the enzymes so

Answer 24

this is a way to inhibit or to decrease bacterial growth.

-Fungi (molds and yeasts) are more resistant than bacteria to high or low osmotic pressure

Question 25

Halophile:

Answer 25

organisms adapted to high salts concentration

Question 26

Obligate halophiles:

Answer 26

require High salt concentration for their growth (30%)

Ex: Dead Sea

Question 27

Facultative halophile

Answer 27

More common
2% salt concentration
Few species of facultative halophiles can tolerate 15%

Question 28

Autotroph:

Answer 28

CO2 is the carbon source

Question 29

• Capnophiles:

Answer 29

require high concentrations of CO2

Question 30

• Heterotroph:

Answer 30

Carbon Source = Organic compounds

Question 31

Nitrogen:

Answer 31

Makes up about 14 % of dry weight of bacterial cell.

-Primarily used to form the amino acids, nucleic acids, and coenzymes

Question 32

-Sources of nitrogen:

Answer 32

NH4+ (ammonium ion), Nitrates NO3-& N2from amino acids and proteins

Question 33

nitrogen fixation;

Answer 33

-Some important bacteria use gaseous Nitrogen N2 directly from the atmosphere -Some organisms that use the nitrogen fixation are free living mostly in the soil but others live cooperatively in Symbiosis with the rots of legumes like alfalfa, beans soybeans,…

Question 34

Sulfur

Answer 34

Considered as a micronutrient
Obtained from organic sources: sulfur containing compounds or from inorganic sources
It’s the constituent of many amino acids and several coenzymes

Question 35

phosphorus

Answer 35

It is essential for the synthesis of nucleic acids & phospholipids of cell membranes
It’s obtained from inorganic sources (inorganic PO4—)

Question 36

Required cofactors for enzymes by microorganisms

Answer 36

Potassium, Magnesium, Calcium

Question 37

a-Obligate aerobes:

Answer 37

Organisms that require oxygen to live

Question 38

b-Obligate anaerobes:

Answer 38

*Bacteria or organisms that are unable to grow or even survive in the presence of oxygen

Question 39

c-Microaerophiles:

Answer 39

•Organisms that grow best when low concentration of oxygen are present

Question 40

d-Facultative anaerobes:

Answer 40

They can live with & without O2 Tend to grow better/faster when O2 is present Can generate ATP by either organic or inorganic means and have the means to detoxify O2
Ex: E.coliin the human intestinal tract

Question 41

e-Aerotolerant anaerobes:

Answer 41

Organisms that are unable to utilize molecular oxygen in their ATP generation but otherwise they tolerate it fairly well

Question 42

Essential organic compounds an organism is unable to synthesize

Answer 42

Vitamins: essentially organic equivalents of trace elemnets
Function as coenzymes
Amino acids, purines, pyrimidines

Question 43

Trace elements

Answer 43

Elements required in relatively small amounts: iron, copper, zinc
Employed as enzyme cofactors
They are sometimes added to a laboratory medium
Usually present in tap water and other components of media