MC5-6: Bacterial metabolism and phototrophy

Question 1

When did bacteria evolve?

Answer 1

Approx. 3.5 billion years ago

Question 2

How many species of animals, plants, and bacteria are there on Earth?

Answer 2

Animals: 10–30 x10⁶

Plants: (estimated) 300,000

Bacteria: (estimated) 10⁷ – 10⁹

Question 3

How many cells are there on Earth at any one time?

Answer 3

4–6 x10³⁰ cells

Question 4

Where are the majority of bacteria and archaea found?

Answer 4

Open ocean: 1.2 x10²⁹

Soil: 2.6 x10²⁹

Oceanic sediment: 3.5 x10³⁰

Terrestrial sediment: 0.25–2.5 x10³⁰

Human guts: approx. 3.9 x10²³

Question 5

Define ‘metabolism’

Answer 5

The set of chemical reactions that occur in living organisms in order to mainain life. Metabolic processes allow organisms to grow, reproduce, maintain structures, and respond to their environments

Question 6

Define ‘catabolism’

Answer 6

Breaking down organic matter, e.g. to harvest energy in cellular respiration

Question 7

Define ‘anabolism’

Answer 7

The use of energy to contruct components of cells such as proteins and nucleic acids

Question 8

What are the three basic requirements for life?

Answer 8

1. Energy source
2. Carbon source
3. Electron source

Question 9

What are the two different possibilities for obtaining energy, and what are the processes that lead to energy obtention?

Answer 9

• Phototrophy – ‘eating’ light energy
  
  • Photosynthesis – converting CO₂ to sugars using sunlight energy
• Chemotrophy – ‘eating’ chemical bond energy
  
  • Respiration – transforming energy from nutrients into chemical energy with O₂ usually as the terminal electron acceptor
  • Fermentation – process of energy production in cell under anaerobic conditions

Question 10

What is the so-called ‘energy currency’ of bacteria, and what are the two methods by which this is generated?

Answer 10

ATP

Substrate-level phosphorylation and oxidative phosphorylation

Question 11

What are the carbon sources of:

1. autotrophs
2. hterotrophs?

Answer 11

1. Autotrophs = CO₂
2. Heterotrophs = organic compounds

Question 12

Where do:

1. photoautotrophs
2. photoheterotrophs
3. chemoheterotrophs
4. chemoautotrophs

get their energy and carbon from?

Answer 12

1. Photoautotroph
   Energy = light
   Carbon = CO₂
2. Photoheterotroph
   Energy = light
   Carbon = organic compounds
3. Chemoheterotroph
   Usually, a single organic compound acts as a source for both energy and carbon
4. Chemoautotroph
   Energy = oxidation of inorganic chemical compounds
   Carbon = CO₂

Question 13

What are the four nutritional categories of life?

Answer 13

• Photoautotroph
• Photoheterotroph
• Chemoautotroph
• Chemoheterotroph

Question 14

Why can O₂ be very harmful to organisms without protective mechanisms?

Answer 14

It is a harsh oxidising agent

Question 15

What is the name for organisms that can grow in oxygen?

Answer 15

Aerobes

Question 16

How do aerobes utilise oxygen?

Answer 16

They use aerobic respiration as their principle energy generation by using O₂ as their terminal electron acceptor

Question 17

Why can anaerobes not live in oxygenated environments?

Answer 17

They never developed protective mechanisms against oxygen

Question 18

Give two examples of environments in which anaerobes live.

Answer 18

• Animal intestinal tract
• Lake/ocean sediments

Question 19

What is different about anoxygenic photosynthesis?

Answer 19

• Carried out in oxygen-free environments
• Electron donor is water
• No oxygen is produced

Question 20

What are the types of aerobic and anaerobic metabolism?

Answer 20

Aerobic

• Aerobic respiration
• Oxygenic photosynthesis
• Anoxygenic photosynthesis

Anaerobic

• Fermentation
• Anaerobic respiration
• Anoxygenic photosynthesis

Question 21

How is ATP generated in bacteria?

Answer 21

Phototrophy

• Pigments absorb energy from the sun
• An electron with a higher energy level is then released from within the pigment
• This electron is passed through an electron transport chain, with the generation of energy by formation of ATP

Question 22

What is the carbon source of:

1. autotrophs
2. heterotrophs
3. mixotrophs?

Answer 22

1. Autotrophs: CO₂
2. Heterotrophs: organic compounds
3. Mixotrophs: both

Question 23

What are the two types of phototrophy and how do they differ?

Answer 23

• Anyoxygenic
  
  • Used bacteriochlorophyll
  • Has 1 reaction centre
• Oxygenic
  
  • Uses chlorophyll
  • Has 2 reaction centres

Question 24

What are the five major groups of prokaryotes that use anoxygenic photosynthesis, and which group used oxygenic photosynthesis?

Answer 24

Anoxygenic

• Purple sulphur bacteriochlorophyll b
• Purple non-sulphur bChl a b
• Green non-sulphur bChl a b
• Green sulphur bChl c d e f
• Heliobacteria bChl g

Oxygenic

• Cyanobacteria chla

Question 25

What do purple sulphur bacteria use as an electron donor? Give examples of the bacteria.

Answer 25

* H₂S * *Thiopedia roseopersicinia* * *Ameobacter purpureus*

Question 26

What do purple non-sulphur bacteria use as an electron donor? Give examples of typical genera.

Answer 26

* Hydrogen * *Rhodospirillum* * *Rhodopseudomonas* * *Rhodobacter*

Question 27

What do green sulphur bacteria use as electron donors? Give examples of species.

Answer 27

* H₂S / S / S₂O₃^2– (which invariably becomes H₂SO₄) * *Chlorobium* species

Question 28

What do green non-sulphur bacteria use as electron donors? Give an example of a species.

Answer 28

* Hydrogen * *Chloroflexus*

Question 29

What do heliobacter use as an electron donor?

Answer 29

H₂S

Question 30

What are the only oxygenic phototrophic prokaryotes?

Answer 30

Cyanobacteria

Question 31

What do cyanobacteria use as an electron donor? Name the two main genera

Answer 31

* Water * *Synechococcus* * *Prochlorococcus*

Question 32

What are the seven reasons for studying microbial metabolism?

Answer 32

1. Medical microbiology 2. Microbiome 3. Diagnostic microbiology 4. Pharmaceutical microbiology 5. Biotechnology 6. Many foods/drugs of plant origin owe their taste/smell/active constituents to microbial metabolism 7. Environmental microbiology

Question 33

How is energy accessed by chemotrophs?

Answer 33

By harnessing and linking oxidation/reduction pairs

Question 34

What does OILRIG mean?

Answer 34

* *O**xidation * *I**s * *L**oss (of electrons) * *R**eduction * *I**s * *G**ain (of electrons)

Question 35

On which side of a redox pair is the oxidised form always written?

Answer 35

Left

Question 36

What is the redox potential and how is it measured?

Answer 36

Redox potential = E'₀ = **the capacity of a pair to donate or accept electrons** Measured electrically by reference to a standard

Question 37

Finish the sentence: Half-reactions with positive redox tend to ______ electrons; half-reactions with negative redox tend to ______ electrons.

Answer 37

Half-reactions with positive redox tend to **donate** electrons; half-reactions with negative redox tend to **accept** electrons.

Question 38

What are the two mechanisms chemoheterotrophs have for energy conservation? What drives the synthesis of ATP in both?

Answer 38

Respiration and fermentation Driven by energy released in redox reactions

Question 39

Describe the oxidase test

Answer 39

* Filter paper impregnanted with redox dye (TMPD) which artificially donates an electron to the cytochrome * The cytochrome system is usually only present in aerobic organisms that are capable of using electron as the terminal electron acceptor * Turns purple if the dye is oxidised by oxygen released from metabolic reaction

Question 40

Where do *Deinococcus* species of bacteria grow?

Answer 40

On sugars, amino acids, organic acids, and mixtures of these

Question 41

What is the best studied of the *Deinococcus* species?

Answer 41

*D. radiodurans*

Question 42

Give two examples of *Spirochetes* and the diseases they cause.

Answer 42

1. *Treponema* – causes syphilis 2. *Borrelia* – causes Lyme disease

Question 43

What is the relevance of *Spricohetes* having a helical structure?

Answer 43

It allows them to move in a corkscrew motion through viscous media such as mucus

Question 44

What do *Planctomyces* lack in their cell walls?

Answer 44

Peptidoglycan

Question 45

What type of prokaryote produce methane?

Answer 45

Methanogenic archaea in anoxic environments

Question 46

What are methanotrophs and methylotrophs?

Answer 46

* Methanotrophs produce methane * Methylotrophs grow on one-carbon compounds including methane

Question 47

What are diazotrophs? Give an example.

Answer 47

Bacteria that reduce nitrogen (N₂) e.g. *Azotobacter*

Question 48

Are *Azotobacter* Gram positive or Gram negative?

Answer 48

Gram negative

Question 49

How do *Azotobacter* contribute to biogeochemical cycling?

Answer 49

They grow on a range of carbohydrates, alcohols, and organic acids and fix N₂ non-symbiotically

Question 50

What are *Rhizobia*?

Answer 50

N₂-fixing symbiont of legumes

Question 51

How are chemoautotrophs specialist?

Answer 51

They can find unique niche zones where chemoheterotrophs cannot live

Question 52

What are the three sources of inorganic electron donors?

Answer 52

1. **Geological** * e.g. volcanic activity producing H₂S 2. **Biological** * Producing H₂S, H₂, NH₃ 3. **Anthropogenic** (human influence) * e.g. agriculture, mining, burning fossil fuels, input of industrial wastes

Question 53

Give examples of the chemoautotrophs that are at the heart of most nutrient cycles

Answer 53

*Aquifex*, nitrosifyers such as *Nitrosococcus*, nitrifyers such as *Nitrobacter*, *Thiobacillus*, *Thiomicrospira*, *Thiothrix*

Question 54

Describe the metabolism of nitrosifiers

Answer 54

They oxidise ammonia to to nitrites

Question 55

Describe the metabolism of nitrifyers

Answer 55

They oxidise nitrites to nitrates

Question 56

Describe the metabolism of sulphur-oxidising bacteria

Answer 56

They oxidise sulphur, using oxygen as a terminal electron acceptor

Question 57

Describe the metabolism of iron-oxidisers

Answer 57

They oxidise iron: * Ferric iron to insoluble ferric hydroxide which precipitates in water * Ferrous iron to ferric state at neutral pH