Eprac 3C: Bacterial Products And Metabolism

Question 1

Microbial metabolism

Answer 1

Microbe obtains energy and nutrients to live and reproduce

Question 2

Aerobe

Answer 2

Able to grow in presence of atmospheric O2

Question 3

Anaerobe

Answer 3

Can grow in absence of atmospheric O2

Question 4

Obligate aerobes

Answer 4

Require O2 for growth

Use O2 as final e acceptor in aerobic respiration

Example: pseudonomas

Question 5

Obligate anaerobes

Answer 5

Do not need or use O2 as nutrient

O2: toxic, kills or inhibits growth

Obligate anaerobic respirator: may live by fermentation, anaerobic respiration, bacterial photosynthesis or methanogenesis

Example: Clostridium

Question 6

Facultative anaerobes

Answer 6

Can switch between aerobic and anaerobic types of metabolism

Under anaerobic: grow by fermentation or anaerobic respiration

In presence of O2: switch to aerobic respiration

Example: escheria

Question 7

Aerotolerant anaerobes

Answer 7

Exclusively utilise anaerobic (fermentative) metabolism but are insensitive to presence of O2

Live by fermentation alone, whether or not O2 is present

Example: Enterococcus faecalis

Question 8

Microaerophiles

Answer 8

Sensitive to normal atmospheric level of O2 (20%)

Require low O2 levels (2%-10%) for growth

Example: Campylobacter

Question 9

Aerobic cultivation

Answer 9

Tryptone soya broth

General purpose liquid enrichment medium

Used in qualitative procedures for assessment of sterility, and for enrichment and cultivation of aerobic and facultatively anaerobic microorganisms that are not excessively fastidious

Question 10

Anaerobic cultivation: candle jars

Answer 10

Incubator

Provides CO2 rich environment essential for growth of microaerophilic anaerobes

Candle is lit before jar is sealed to use up available O2 within jar

Question 11

Anaerobic cultivation: Anaerobic incubators

Answer 11

In conjunction with Oxiod AnaeroGen sachets

Convenient and reliable product for rapid generation of an aerobic environment (essential for growth of fastidious anaerobes)

When sealed -> AnaeroGen sachet rapidly absorbs oxygen within jar whilst generating CO2

Question 12

Anaerobic cultivation: Anaerobic gloves boxes

Answer 12

Anaerobic systems contain oxygen free work area in incubator

Interchange compartment allows materials to be transferred inside without exposing interior to oxygen

Anaerobic atmosphere is maintained by vacuum pump and nitrogen purges

Question 13

Anaerobic cultivation: Thioglycollate (THIO) broth medium

Answer 13

Rich medium containing yeast extract, peptone and dextrose -> support growth of most organisms

Also contains sodium thioglycollate which rapidly oxidises, removing O2 from medium. Encourages growth of strictest anaerobes such as Clostridium by maintaining low oxygen potential without requiring special seal on vessel

A small conc of Resazurin (indicator of redox potential: the amt of oxidation in medium shown through amt of red colour). If >20% of uppermost portion of stored medium turned red -> anaerobic conditions may be restored by heating in boiling water bath

Changes from yellow to red

Question 14

Importance of nitrogen cycle

Answer 14

Nitrogen: fundamental component of protein, nucleic acids and other biochemicals in plants, animals and microbes

Plants, animals and microbes vary in capacity to utilise nitrogen in its various forms

Some forms of nitrogen can be toxic

Question 15

Nitrogen fixation

Answer 15

Carried out by limited range of free-living (Clostridium, Vibrio, and Pseudomonas) and symbiotic (Rhizobium) heterotrophic bacteria as well as photosynthetic cyanobacteria and phototrophic bacteria

Nitrogen fixing enzyme: nitrogenase. Sensitive to oxygen -> occurs in oxygen-free habitats (soils, sediments and roots) or in specialised structures in cyanobacteria (heterocysts)

Question 16

Symbiotic nitrogen fixing bacteria

Answer 16

Example: Rhizobium

Occur in root nodules of leguminous plants (example: Clover)

Question 17

Symbiosis

Answer 17

Relationship between legumes and their root nodule bacteria

Called symbiosis because plant and bacteria live in close, mutually beneficial association

Question 18

Legumes

Answer 18

Produce rich supply of oxygen binding, haemoglobin-like, pigment: leghaemoglobin inside root nodules

Leghaemoglobin supplies nodule bacteria with oxygen to fix nitrogen while keeping oxygen away from nitrogen fixing enzyme nitrogenase, facilitating efficient symbiotic nitrogen fixation

Question 19

Nitrogen fixing nodules

Answer 19

Can be identified by reddish pink internal colour of nodule

Question 20

Non-symbiotic nitrogen fixation

Answer 20

Nitrogen is converted to NH3 bh aerobic bacteria such as Azotobacter

Question 21

Azotobacter

Answer 21

Gram -ve rods

Capable of fixing atmospheric N2 when growing in nitrogen-free medium

Form large cysts which make them more resistant to adverse environmental conditions

Use mannitol as energy source to fix nitrogen

Question 22

Nitrification

Answer 22

NH3 (nitrosomonas) -> NO2- (nitrobacter) NO3-

Largely limited to 2 pops of aerobic autotrophic bacteria, deriving energy coupled to carbon fixation

Nitrosomonas and nitrobacter: dominant bacteria involved

Occurs in aerobic habitats

Question 23

Denitrification

Answer 23

NO3 -> NO2 -> N2O -> N2

Occur predominantly in anaerobic habitats

Only carried out by some heterotrophic organisms (Bacillus and pseudomonas) or chemolithotrophic bacteria (e.g Thiobacillus)

Question 24

Fermentation

Answer 24

Process where microorganisms use to convert sugars into simpler organic compounds-> ATP

2 types fermentation: lactic acid and ethanol fermentation

Most use lactic acid: lactose + water -> lactic acid

Yeasts and some bacteria use ethanol fermentation: glucose -> 2 ethanol + 2 CO2

Question 25

Cheese (lactic acid fermentation)

Answer 25

Produced from protein (casein) and fats in milk

Milk is collected and pasteurised to remove potentially harmful bacteria -> acidified through addition of bacterial starter cultures (typically Lactobacilli and Streptococci which ferment milk lactose -> lactic acid)

During maturation, some cheeses are inoculated with mould such as Penicillium camemberti or Penicillium roqueforti -> adds to texture and flavour of cheese and helps in preservation

Question 26

Yoghurt (lactic acid fermentation)

Answer 26

Relies on bacterial starter cultures (Lactobacilli and Streptococci): added to pasteurised milk

Lactose fermented -> lactic acid

Still teeming with live bacteria (probiotics) when eaten

Question 27

Cured meats (lactic acid fermentation)

Answer 27

Processed to preserve meat (through drying, smoking or fermentation)

Active water content and acidity prevent growth of most bacteria -> safe to eat

Prepared by mixing sugar and cultures of lactic acid bacteria into mince -> incubated in warm humid room -> allow bacteria to grow and ferment sugars. Once pH of sausage dropped to 4.2 -> dried to lower water content before storage or eating

Coated with Penicillium to enhance flavour and length of preservation of sausage

Question 28

Yeasts (ethanol fermentation)

Answer 28

Yeasts: unicellular fungi . Reproduce by budding

Able to ferment sugars to produce alcohol and CO2

Question 29

Beer (ethanol fermentation)

Answer 29

Yeasts used to ferment grain sugars -> produce alcohol and bubbles

Different yeasts used to affect flavour and foaminess

Brewing top fermenting yeast such as Saccaromyces cerevisiae, at warm temp for short periods produce strong cloudy beer

Using bottom-fermenting yeast (such as Saccharomyces carlsbergensis): brew at lower temps for longer periods -> prevents production of fruity esters and other by-products. Creates beers with more crisp and mellow taste

Question 30

Wine (ethanol fermentation)

Answer 30

Major yeast used: Saccharomyces cerevisiae

Different strains produce different types of wine as each can produce different by products from fermentation of multiple types of sugars

Presence of wild yeasts in ferment (such as Candida or Brettanomyces) acquired from vineyard or vectors such as fruitfly, can produce additional by-products -> add to complexity of wine. But in large quantities can make wine undrinkable -> contamination with wild yeast usually avoided

Question 31

Bread (ethanol fermentation)

Answer 31

Yeasts (usually strains of Saccharomyces cerevisiae) ferment sugars and produce CO2 -> bubbles within dough -> dough to rise or leaven

By products produced by yeast add to flavour and aroma of bread

Yeast can be added as pure liquid culture or as dried powder, or sample of previous days leavened dough can be mixed in

During baking: active yeast cells die but remain within bread -> additional nutrients and flavour