Lecture 3 - Metabolism and bacterial pathogenesis: respiration and stress

Question 1

What determines the environment that is occupied by a bacterial species?

Answer 1

Depends on the metabolic capabilities of that species -the microbe can grow if it has the appropriate metabolic machinery However: the microbe may affect its environment to suit its needs

Question 2

Describe the relationships as demonstrated by the three arrows on this image of a microbe interacting with its host and environment

Answer 2

1. The micro-organism interacting with its abiotic environment. Bacteria recurit carbon sources from the environment and change their environment e.g. A large number of bacteria present in an environment would alter the oxygen levels available to bacteria
2. The micro-organism interacting with other bacteria in its environment. May have a competitive or co-odinated relationship
3. The micro-organism interacting with its host. May be seen as a 2-way process but in reality whilst the microbe recieves things from its host it also actively changes the environment of the host to suit its needs, e.g. resulting in tissue degradation or diahrea (Shigella dysenteriae)

Question 3

Give an example of a major determinant of pathogen nutrition and lifestyle

Answer 3

Oxygen availability

Question 4

How is oxygen availability a major determinant of pathogen nutrirtion and lifestyle?

Answer 4

• the human body is carbon rich (therefore an attractive site for micro-organisms) and therefore the oxygen levels often become a limiting factor for growth
• Each cell of a species has the same demand for oxygen but as they grow and multiply, diffusion is unable to supply sufficient oxygen to support the metabolism of carbon substrates to CO₂

_-In this way, the bacterial metabolism has defined the environmental oxygen limitation

• colon, oral cavity
• O deficient inside biofilms

Question 5

Give an example of a site in the human body where Oxygen is often a limiting factor in microbial nutrition and lifestyle

Answer 5

In the large intestine

In the oral cavity

Question 6

Aside from locations within the human body, where does low oxygen availability also occur

Answer 6

Inside bacterial biofilms

Question 7

What is respiration?

Answer 7

A highly efficient way of conserving biological energy using ATP from Glucose

Typically with the intake of oxygen and the release of carbon dioxide from the oxidation of complex organic substances.

Question 8

What is the basic process of respiration?

Answer 8

Glucose is converted to pyruvate which enters the citric acid cycle to produce Carbon dioxide and NADH which is oxidised to produce:

Probably 38 ATP per 1 glucose

but possibly

30 ATP per 1/2 glucose

Question 9

What is oxidation ?

Answer 9

The gain of oxygen or the loss of electrons

Question 10

What is reduction?

Answer 10

The loss of oxygen or the gain of electrons (reduction in the charge)

Question 11

What occurs (in respiration) in the absence of oxygen?

Answer 11

In the absence of O₂ all NADH that would otherwise have been reduced accumulates and remains as NADH

Bacteria may use the process of fermentation instead

Question 12

When does fermentation occur?

Answer 12

When there is no net electron acceptor (O₂) and the cell cannot dispose of the accumulated NADH from the citric acid cycle

• cell must instead recycle the NADH
• results in a limited ability to make ATP

Question 13

What is the process of fermentation?

Answer 13

1. Glucose is converted to Pyruvate in the process of glycolysis, creating one ATP molecule and an NADH, which cannot be used as there is no end electron acceptor
2. Pyruvate can then either be:
   a. Converted to lactate and NADH oxidised to NAD+
   b. Reduced to acetate and ethanol
   c. Reduced to just ethanol
3. These processes return a smaller amount of ATP compared to aerobic respiration

Question 14

What is produced when Glucose is converted to Lactate?

Answer 14

This is a redox balanced system in that:

1 glucose results in 1 lactose molecule and 1 ATP molecule

Question 15

Why is aerobic respiration good?

Answer 15

Can makes lots of ATP from one glucose molecule, 38 ATP from 1 glucose molecule

-probably-

Basically a lot more than fermentation

Question 16

Why is fermentation not as good as respiration?

Answer 16

Produces only 2 ATP per glucose molecule compared to the 38 produced by respiration

-Probably-

Question 17

How is motive force generated by oxygen respiration?

Answer 17

• redox reductions are coupled to proton motive force
• proton motive force is coupled to ATP production

Question 18

Where is the arrangement to generate proton motive force found?

Answer 18

Found in the mitochondria and many bacteria

Question 19

How does the respiratory chain differ in E.coli?

Answer 19

E.coli has a simplified version of the respiratory charin

• no bc1 complex or cytochrome c
• retains NADH dehydrogenase, quinol and oxidase (oxygen reductase)

Question 20

What are essentials of the stress response in bacteria?

Answer 20

Dispatch, destroy, diversify or die

And

Respond and regulate

Question 21

Explain the dispatch, destroy, diversify or die response of bacteria to stress

Answer 21

Dispatch and destroy: When bacteria use enzymes or a release of proteins to mediate stress e.g. enzymes to degrade antibiotics, proteins to stabilse structures under heat stress

Diversify: When bacteria alter themselves in response to a stress to be able to survive under that stressor

Question 22

What are the three ways a bacteria can react to stressors?

Answer 22

1. Use enzymes to degrade stressor e.g. antibiotic
2. transport stressor out of the cell
3. Alter themselves

Question 23

What is oxidative stress?

Answer 23

Every aerobic organism undergoes oxidative stress when electrons leak from the respiratory chains and catalyse O₂ to O₂^- . These are the highly toxic intermediates of the conversion of O₂ to water and include superoxide O₂- peroxide O₂^2- and an hydroxyl radical OH^. . These are short lived radicals with an unpaired e^- . These can be formed internally (O₂ to H₂O, or in a macrophage oxidative burst) or taken up externally.

Question 24

What are the possible origins of oxidative stress?

Answer 24

• leaking of e^- from the respiratory chain catalysing O₂ to O₂-
• Generated purposely by host macrophages (the oxidative burst by NADH oxidase)
• By other bacteria e.g. Streptococcus which produces pyruvate oxidase to outcompete other bacteria

Question 25

How does oxidative stress cause damage?

Answer 25

The short lived oxygen radicals are highly reactive and can cause cellular damage. Superoxide can react with itself to form peroxide which then binds to amino acids and results in DNA damage

Question 26

How is macrophage attack a source of oxidative stress?

Answer 26

• Macrophages identify and kill invading pathogens through the innate immune response
• Get the generation of an oxygen superoxide (O₂-) via the NADPH oxidase in an oxidative burst
• generation of radical nitric oxide (NO-) by inducible NO synthase (nitosative burst)

Question 27

What is the response of enteric bacteria to the toxic intermediates superoxide, peroxide and hydroxyl radicals?

Answer 27

Have sensory systems for superoxide (SoxRS) and peroxide (OxyR) to up-regulate superoxide dismutase and peroxidases/catalases

Question 28

When does nutrient depravation occur in bacteria?

Answer 28

In the absence of sufficient oxygen, bacteria may then become nutrient starved

Question 29

How do facultative anaerobes (e.g. the enteric bacteria) respond to nutrient depravation?

Answer 29

Regulate gene expression to synthesise alternative respiratory pathways under anearobic conditions

e.g. the anaerobic regulator in E.coli is FNR in E.coli

E.coli use up oxygen first then must switch on the expression of other enzyme genes using FNR

Question 30

What is the FNR enzyme in bacteria?

Answer 30

The fumerate and nitrate reductase regulator

Question 31

How does the FNR enzyme act?

Answer 31

1. Aerobically, FNR exists as a monomeric protein
2. Anaerobically, FNR dimerises and contains an oxygen sensitive iron sulfur cofactor
3. FNR binds to promoters and activiates the expression of genes required under anaerobic conditions

Question 32

Hey how you doin