Microbial Growth

Question 1

What are the main requirements for microbial growth?

Answer 1

Physical requirements - temp, ph and osmotic pressure

Chemical requirements. CHOPSN, trace elements and organic growth factors

Question 2

List the 5 classes of microbes by temp and the 3 important temp factors

Answer 2

Psychrophiles - between -10 and 20 degrees 
Psychrotrophs - between 0 and 30 degrees
Mesophiles - between 10 and 50 degrees
Thermophiles - 40 and 70 degrees
Hyperthermophiles - 68 and 110 degrees

They have minimum, optimum and maximum growth temps

Question 3

How and why is the pH of a culture media controlled?

Answer 3

Majority of bacteria grow at a pH between 6.5 and 7.5
Fungi prefer acidic
Acidophilus grow in very acidic conditions
PH of artificial medium is controlled by addition of a buffer
When bacteria are cultured, they produce acid which interferes with their own growth. Main pat in a proper ph, chemical buffers

Question 4

What is the importance of osmotic pressure and name the microbes that respond to it.

Answer 4

Will depend if the cell swells or shrinks due to osmosis
Hypertonic environments cause plasmolysis
Most microbes inhibited by high salt
Halophiles love
Saccarophiles love sugar and are usually fungi
Extreme or obligate halophiles require high osmotic pressure
Facultative halophiles tolerate high osmotic pressure

Question 5

Describe the use of the macronutrients in cell growth

Answer 5

Nitrogen - amino acids, proteins, DNA and rna
Carbon - carbs, lipids, catabolism and anabolism
Hydrogen - counter ion, proton source for atp
Oxygen - found in most organic molecules and as terminal electron acceptor
Phosphorus - found in atp, nadp, DNA and rna
Sulphur - amino acids and cofactors

Question 6

Name the trace elements and their role in microbes

Answer 6

Inorganic elements required in small amounts
Iron - required for cytochromes in electron transport
Magnesium - counter ion, nucleotides and atp and cofactors to enzymes
Zinc
Cobalt
Copper
Molybdenum

Question 7

How do anaerobes avoid damage from toxic O2 species?

Answer 7

1. Singlet oxygen. Is O2 boosted to a higher energy state
2. The super oxide radical is O2-.
   Superoxide dimustase converts it to H2O2 which is highly toxic
3. Peroxide anion - O22- is toxic, removal of H2O2 removes it via a catalase
   2H2O2 To 2H2O and O2
   Or via peroxidase from H2O2 and 2H+ via peroxidase to 2H2O
4. Hydroxyl radical (oh)
   - formed by ionising radiation

Question 8

Describe the 5 different microbes based on oxygen requirements

Answer 8

Obligate aerobes - aerobic growth only, stay at top
Facultative anaerobes - both anaerobic and aerobic growth. Most growth in oxygen
Obligate anaerobes - only anaerobic growth, far away from o2
Aerotolerant anaerobes - only anaerobic but will proceed in presence of O2
Microaerophiles - only aerobic, O2 required on low concentrations

Question 9

Explain the purpose of organic growth factors?

Answer 9

They are organic compounds obtained from the environment
Eg, vitamins, purines, prymidines
Amino acids
Some microorganisms absolutely need a particular vitamin
Most do not require any growth factors

Question 10

Describe culture media and the 7 groups of microbes etc that arise from the use of this media

Answer 10

Culture medium is nutrients prepared for microbial growth
Sterile - no living organisms
Inoculm - intro to microbes to the medium
Culture - microbes growing in/on culture medium
Pure culture - contains only one species or strain
Colony - population of cells arising from a single cell or spore or from a group of attached cells
Colony forming unit - measure of the number of living cells in a sample that will grow, divide and form colonies

Question 11

Describe agar

Answer 11

Complex polysaccharide made from agar agar seaweed
Used as solidifying agent for culture medium in petri plates, slants and deeps
Generally not metabolized by microbes
Liquefies at 100 degrees
Solidifies at approx 40 degrees

Question 12

What is the difference between chemically defined media for bacterial growth and complex media for bacterial growth?

Answer 12

Chemically defined - the exact chemical composition of the medium is know
Complex - exact composition is unknown. Not easily reproducible, they vary from peptones to peptone

Question 13

What is the difference between selective media and differential media?

Answer 13

Selective - suppress unwanted microbes and encourage desired microbes
Differential - an indicator in the medium allows detection of a bacterial trait

Question 14

What is enrichment culture and its purpose?

Answer 14

Encourages
the growth of desired microb or class of microbes
Designed to increase very small number of the desired type of organism to detectable levels.

Question 15

Describe anaerobic reducing media?

Answer 15

Important for anaerobes that might be killed by O2.
Chemicals such as cysteine, sulphide
They can be added to growth medium to remove O2 by reaction.
O2 is lower in solubility with high temps, therefore high temp reduces O2 partial pressure in growth medium

Question 16

Justify the use of an anaerobic jar.

Answer 16

Maintenance of high CO2 levels

Perfect for capnophiles

Question 17

Describe the anaerobic chamber?

Answer 17

Atmosphere physically and chemically stripped of O2
Usually a device to measure and report O2 content in parts per million
Atmosphere may be - N2 almost inert, co2, H2O for catalytic conversion of any liberating o2 to water

Question 18

Justify the use of the candle jar.

Answer 18

Perfect for capnophiles.
They require high CO2 conditions
CO2 packet can be used to establish the condition

Question 19

Define colony and how to obtain pure cultures?

Answer 19

Colony is a population of cells arising from a single cell or spore or from a group of attached cells
A pure culture contains only one species or strain
A viable cell is often called a colony forming unit as it will form a colony
The streak plate method is used to isolate pure cultures

Question 20

Describe the 4 phases of microbial growth/generation time

Answer 20

Phase 1- lag phase, where little cell division is occurring
Phase 2- exponential or log growth phase
Phase 3.- stationary phase where bacterial death = bacterial divion rate
Phase 4- death phase where cell lysis occurs. Also a log phase

Question 21

Describe the different types of reproduction for prokaryotes

Answer 21

Binary fission
Budding
Conidiophores (actinomycetes)
Fragmentation of filaments

Question 22

Describe the 4 steps in binary fission

Answer 22

1. Cell elongates and DNA is replicated
2. Cell wall and plasma membranc begin to constrict
3. Cross wall forms, completely separating th DNA copies
4. Cell separates

Question 23

What are the 4 methods of measuring cell growth

Answer 23

1. Plate counts
2. Membrane filtration
3. Direct count under microscope
4. Turbidity measurement in spectrophotometer

Question 24

Describe plate counts and how to count from them

Answer 24

Indirect, counts viable cells, takes time, must first be incubated so they can grow visible colonies
Bacterial cells are serially diluted
Dilutions spread into plates and grown
The dilution that has between 25-250 colonies is counts
Count x dilution = number of bacteria present

Question 25

Describe membrane filtration and how to count from them

Answer 25

Indirect, viable cells, takes time
Water is filtered by vacuum onto a membrane
The membrane is placed onto an agar plate and incubated
Colonies are counted

Question 26

Describe direct plate counts and how to count from them

Answer 26

Petroff- hausser counting slide
No incubation time is needed to count
Cannot differentiate viable from non viable cells

Question 27

Describe turbidity, measurement from a spectrophotometer

Answer 27

Bacterial sample placed into a spec cuvette
The optical density read at 600nm is read
The number bacteria/mL Is calculate by comparison of
Reading to a standard curve for the particular bacterium