Association of bacteria with other organisms: commensals, symbionts & pathogens I

Question 1

What is infection

Answer 1

Colonisation of the host

Question 2

What is transmissbility

Answer 2

The ability to spread from host to host

Question 3

Carriage

Answer 3

The establishment of harmless long term relationship

Question 4

Disease

Answer 4

Infections that damage the host

Question 5

Pathogenicity

Answer 5

Ability to cause disease

Question 6

Virulence

Answer 6

Severity of disease caused

Question 7

Commensal

Answer 7

Shares its food (parasites feed on body of host)

Question 8

Symbiosis

Answer 8

Association of two different organisms and contribute to each other’s support

Question 9

How does syntrophy explain a possible mechanism for the origin of eukaryotes and multicellularity

Answer 9

Highly nutritionally interdependent communities of eubacteria and archaea exist in anoxic environments

Patterns of gene exchange –> may not be wholly independent organisms

Question 10

What are the stages of host adaptation

Answer 10

1. Free living and extra cellular
2. Facultative intracellular
3. Obligate intracellular
4. Obligate intracellular mutualist
5. Organelle

Question 11

What are diatoms and what are they predominantly associated with

Answer 11

• Abundant microscopic algae - contribute about 20% photosynthesis
• Associated with proteobacteria and bacteriodetes

Question 12

How have bacteria contributed to diatom genomes

Answer 12

Via HGT

Question 13

Metabolic interactions between diatom and bacteria include:

Answer 13

Parasitism
Synergism
Competition

Important in biogeochemical cycles

Question 14

Bacterial and fungal associations : lichens

Answer 14

• Mycobiont: protection of photobiont and absorb mineral nutrients
  roles of prokaryotic photobiont

Question 15

Legumes and rhizobium

Answer 15

Important biological symbiosis and species specific

Question 16

What is the role of the plant

Answer 16

Provide nutrition

Question 17

Role of bacterium

Answer 17

nitrogen fixation

Question 18

How are rhizobium root nodules formed

Answer 18

• Recognition and attachment
• Signalling
• Invasion
• Travel through infection thread
• Bacteriod formation
• Bacterial and plant growth to form the nodule

Question 19

Outline verminephrobacter symbiosis in earthworms

Answer 19

Almost all earth worms have species-specific endosymbionts

• Vertically transmitted
• Bacteria live on host waste products - beneficial for host reproduction because of nutritional advantage conferred to host
• Reductive evolution of bacterial genome results in streamlining

Question 20

Insect endosymbionts

Please outline the extent of aphids’ dependence on buchnera

Answer 20

Buchnera are obligate intracellular endosymbionts of aphids
Aphids die without bacteria (eg can be killed by antibiotics)
Bacteria are maternally transmitted
Most buchnera genes have close homologues in the enteric bacteria - ancestor like e.coli that has undergone reductive evolution

Question 21

Please outline the host and symbiont roles in the metabolic interdependence of aphids and buchnera

Answer 21

The host supplies energy, carbon, nitrogen in the form of glutamine from the phloem (aphids feed on trees)

Symbiont role: production of amino acids especially tryptophan (12 -16 copierss of trpEG genes)

Question 22

What is the evidence of long term co-speciation between endosymbionts and insect hosts

Answer 22

Mutualistic symbiosis
150-250 million years ago
Vertical transmission of symbionts (from parent to offspring)
Coevolution of bacteria and host.- similar aphid and symbiont phylogenetic trees

Question 23

What is the evidence of long term co-speciation between endosymbionts and insect hosts

Answer 23

Mutualistic symbiosis
150-250 million years ago
Vertical transmission of symbionts (from parent to offspring)
Coevolution of bacteria and host.- similar aphid and symbiont phylogenetic trees

Question 24

What happens in wolbachia infection

Wolbachia induced cytoplasmic incompatibility

Answer 24

Causes a modification in the sperm that can be rescued by eggs of infected females - uninfected embryos die

Question 25

What is meant by Wolbachia existing as an endosymbiont

Answer 25

It maintains a neutral relationship with the host

can act as mutualise, commensalism, or pathogen

Question 26

Please outline cytoplasmic incompatibility

Answer 26

CI results in infected females having a selective advantage over uninfected females since the bacteria is only transmitted via the female germline . Uninfected females mating with infected males produce inviable embryos

Question 27

Wolbachia vector controlled strategies

Answer 27

Switches a wild population of mosquitoes with a pathogen free one through Wolbachia induced CI
Release of just Wolbachia infected males leads to high levels of CI and reduction in total vector population

Question 28

What is cellulose degradation

and why does it form the base of a number of symbioses

Answer 28

Carbohydrate polymers are abundant.- for storage and structural components

Insoluble crystalline microfibrils - highly resistant to enzyme hydrolysis. Metabolic pathways to utilise cellulose has evolved in many bacterial groups

Question 29

What are symbiotic associations between termites and the microbitota in their gut important for?

Answer 29

utilise complex biopolymers such as wood
Flagellates and bacteria occur in the gut of lower termites while higher termites possess only bacteria
Spirochetes are abundant in the termite gut

Question 30

Communities of microbes are important for what in ruminants?

Answer 30

The digestion of cellulose

Question 31

What is the rumen

Answer 31

A large fermenter kept at constant temperature

Question 32

How many hours does it take for the plant material to be digested?

Answer 32

9-12 hours

Question 33

A variety of bacteria convert polymers such as cellulose to what>

Answer 33

glucose and then fatty acids