Lec 14: Bacterial nutrition, culture media & cultivation

Question 1

Nutrition in bacteria influenced by..

Answer 1

Sources of carbon, e- & external energy for growth

Diversity of chemicals needed to make bacterial cell components

The need for growth factors

Question 2

Carbon

Answer 2

The backbone of organic molecules

Question 3

Electrons

Answer 3

Electron flow in bio reactions -> energy

Needed to reduce molecules during biosynthesis

Question 4

External energy source

Answer 4

Necessary to power cell

Make ATP

Question 5

Autotroph

Answer 5

Carbon source: CO2

Question 6

Heterotroph

Answer 6

Carbon source: organic molecules made by other molecules

Question 7

Phototroph

Answer 7

Energy source: light

Question 8

Chemotroph

Answer 8

Energy source: Exergonic (heat or energy is released) chemical reactions (oxidation of organic or inorganic compounds)

Question 9

Lithotroph

Answer 9

Electron source: reduced inorganic molecules

Question 10

Organotroph

Answer 10

Electron source: organic molecules

Question 11

Carbon

Answer 11

Found in: most cell structure (e.g cell wall) & functional chemicals (e.g DNA)

External sources (come from): CO2 (inorganic), simple & complex sugars (organic)

Question 12

Nitrogen

Answer 12

Found in: proteins, nucleic acids, some polysaccharides & lipids

External sources: NH4+, NO3, N2 (inorganic). Proteins, AA, urea (organic)

Question 13

Hydrogen

Answer 13

Found in: organic compounds

Come from (external sources): organic compounds, H2O

Question 14

Oxygen

Answer 14

Found in: organic compounds and electron transport chain (respiration)

Come from (external source): H2O, CO2, O2

Question 15

Sulphur

Answer 15

Found in: S-AA (methionine, cysteine) & vitamins (biotin, thiamine)

Come from: SO4 (inorganic). Cysteine, methionine (organic)

Question 16

Phosphorus

Answer 16

Found in: nucleic acids, phospholipids, ATP

Come from PO4

Question 17

K, Ca, Mg, Fe

Answer 17

Found in enzymes & ribosomes

External sources: as ions in solutions (e.g K+)

Question 18

Micronutrients or trace elements

Answer 18

Mn, Zn, Co, Ni, Cu

Found in: cofactors (helper molecules; bind to & assist enzymes to function properly)

Come from: as ions in solution

Question 19

Problems for cell in uptake of nutrients by bacteria

Answer 19

Microbes can only take in dissolved molecules (must take in nutrients from dilute solutions against conc gradient)

Cytoplasmic membrane prevents passage of most substances

Enormous variety of nutrients

Nutrient uptake mechanisms should be specific

Question 20

Bacteria mechanisms for nutrients uptake across membrane

Answer 20

Passive diffusion

Facilitated diffusion (ATP not required)

Active transport (ATP required)

Group translocation (ATP required). Transport of solute molecules to higher conc in which molecule is chemically modified during transport

Question 21

Facilitated diffusion

Answer 21

Diffusion across membrane involving carrier protein

Carrier protein in outward facing conformation binds to solute -> changes conformation to inward facing conformation -> releases solute into cell

Question 22

Active transport

Answer 22

Transport of solute molecules to higher conc (against conc) using transport proteins

ATP energy required

After binding solute -> solute binding protein approaches ATP binding cassette (ABC) transporter -> protein attaches to transporter and releases solute -> energy released by hydrolysis of ATP -> movement of solute across membrane

Question 23

Effect of environmental factors on microbial growth when culturing: oxygen

Answer 23

Some bacteria & most multicellular organisms are aerobic, some are anaerobes

Question 24

Aerotolerant anaerobes

Answer 24

grow equally well in presence or absence of oxygen

Question 25

Obligate anaerobes

Answer 25

grown only when oxygen is absent

Question 26

Facultative anaerobes

Answer 26

do not require oxygen. Can grow with or without oxygen. Most grow better aerobically (energy production better in oxygen)

Question 27

Microaerophiles

Answer 27

damaged by atmospheric O2 and require O2 for growth

Question 28

Effect of environmental factors on microbial growth when culturing: Temperature

Answer 28

Microbes cant regulate their internal temp -> affected by external temps Enzymes vary in temp sensitivity High temp -> membrane degrades Low temp -> membrane becomes solid

Question 29

Psychrophile

Answer 29

Cold environments Grow well at 0 degrees, optimum ~15 degrees

Question 30

Psychrotolerant

Answer 30

Cold environments Grow at 0 degrees Optimum ~25 degrees

Question 31

Mesophiles

Answer 31

Moderate temps Optima ~20-45 degrees

Question 32

Thermophile

Answer 32

High temps Optima ~55-65 degrees

Question 33

Hyperthermophile

Answer 33

Very high temps Optima ~85-113 degrees

Question 34

Design of culture determined by..

Answer 34

Sources of carbon, electrons & external energy used for growth Diversity of chemicals needed to make bacterial cell components The need for growth factors

Question 35

Agar

Answer 35

A carbohydrate, extracted from red algae Usually added to liquid broth medium Dissolves at 90 degrees Sets at ~45 degrees, stable from 0-80 degrees when set Easily sterilised Not degraded by bacteria Spread plate, streak plate, or pour plate yields single isolated colonies

Question 36

Culture media classified based on..

Answer 36

Chemical composition: defined (synthetic), complex Physical nature: liquid, semisolid, solid Function: supportive, enriched, selective, differential

Question 37

Defined or synthetic media

Answer 37

A medium in which all components are known

Question 38

Complex media

Answer 38

Medium containing some ingredients of unknown chemical composition Formulated to support growth of wide range of bacteria Used where nutritional requirements of particular organism are known Examples: nutrient broth/agar, tryptic soy broth/agar (TSB/TSA), MacConkey agar Typically made from protein digests & meat extracts

Question 39

Selective media

Answer 39

Have ingredients/conditions which inhibit growth of unwanted microbes & favour growth of specific organisms Bacteria may also be selected by incubation with nutrients they specifically use

Question 40

Differential media

Answer 40

Distinguish between different genera or species based on biological/metabolic properties Often contain acid-base indicators & selective agents -> limit range of bacteria growing Example: mannitol salt agar. Staphylococcus aureus ferments mannitol -> produce acids-> pH indicator goes from red to yellow. Non-pathogenic staphylcocci remain red

Question 41

Supportive media

Answer 41

Support growth of many microorganisms E.g TSB or TSA

Question 42

Enriched media

Answer 42

Blood & other nutrients are added to general purpose media -> encourage growth of fastidious microbes Blood agar: horse/sheep blood. Enriched and differential (alpha, beta, gamma haemolysis) Chocolate agar (contain lysed blood cells)

Question 43

MacConkey agar

Answer 43

Example of complex media Use bile salts & dye crystal violet -> inhibit Gram +ve and not Gram -ve Example of differential media Have lactose & neutral red dye: lactose-fermenting (e.coli) colonies: red; non-fernenters (salmonella) are colourless