Metagenome

Question 1

What is genomics?

Answer 1

→ The whole cell content

Question 2

What is transcriptomics?

Answer 2

→ whole cell gene expression

Question 3

What is proteomics?

Answer 3

→ Whole cell protein content

Question 4

What is metabolomics?

Answer 4

→ cell metabolite content

Question 5

How do you purify DNA?

Answer 5

→ Culture the organism in isolation

Question 6

Why in practise is DNA not able to be purified?

Answer 6

→ organisms do not live in isolation

→ they are a complex mixture of species

Question 7

What is a microbiota and what does this include?

Answer 7

→ Ecological community of commensal and pathogenic microorganisms
→ bacteria, archae, prostists, fungi and viruses

Question 8

What is a microbiome?

Answer 8

→ Collective genomes of the microorganisms in these communities

Question 9

What diseases have changes in the microbiome been associated with?

Answer 9

→ Cancer
→ Depression
→IBS

Question 10

What can gut microbiome classify?

Answer 10

→ individuals as being obese or lean

Question 11

What are early life gut microbiomes linked with?

Answer 11

→ Development of allergic conditions such as asthma

Question 12

What are the 4 human microbiomes?

Answer 12

→ Gut microbiome
→ Skin microbiome
→ Oral microbiome
→ Vaginal microbiome

Question 13

What can cure a clostridium difficile infection and why?

Answer 13

→ Stool transplant

→ the microbiome in CDI is different to a healthy microbiome

Question 14

Why is 16S targeted PCR used?

Answer 14

→ 16S is a ribosomal component of the 30S subunit in prokaryotes
→ all bacteria have the 16S subunit

Question 15

Describe how 16S targeted PCR amplification works?

Answer 15

→ Sample (urine, blood, etc)
→ DNA is extracted from a mixed population of bacteria in the sample
→ 16S PCR amplification - the 16S gene amplifies
→ sequence the PCR

Question 16

Why are there biases in 16S PCR?

Answer 16

→ Some bacteria purify better than others

→ some sequences amplify better than others

Question 17

What is done with the sequences after 16S PCR?

Answer 17

→compared to a database of known 16S sequences

Question 18

What bacteria changes during the first year of life and how?

Answer 18

→ Actinobacteria drops after the first years of life

Question 19

What bacteria is present in babies when breastfeeding?

Answer 19

→ Bifidobacteria

Question 20

What 2 things do you need to consider when doing PCR on a bacterial variable region?

Answer 20

→ If it contains enough information to separate the genus

→ amplicon length

Question 21

Why is sequencing a smaller region better?

Answer 21

→ The sequencer can read it twice and any errors will cancel out because the two sequences are combined into one region

Question 22

What are disadvantages to the 16S method?

Answer 22

→ It is sensitive to contamination

Question 23

What is the 16S method used for?

Answer 23

→ Low biomass sample

Question 24

How do you mitigate contamination?

Answer 24

→ Randomise the samples
→ Note batch numbers of reagents
→ Sequence negative controls

Question 25

What are the disadvantages of long reads?

Answer 25

→ they have higher error rates and introduce noise

Question 26

What is whole genome shotgun sequencing?

Answer 26

→ Sequencing all the genes not just the 16S

Question 27

How does whole genome shotgun sequencing work?

Answer 27

→ It sequences bacteria, viruses and fungi
→ the genes are then assembled back together
→ you can assess the DNA taxonomically
→ overlay it on pathways
→ changes in metabolic pathways between species

Question 28

What are you looking for in whole genome shotgun sequencing?

Answer 28

→ changes in metabolic pathways between species

Question 29

What are the 3 issues with whole genome shotgun sequencing?

Answer 29

→ Host cells are in excess
→ no amplification step to enrich for bacterial DNA
→ sample dependent

Question 30

How do you enrich without amplification (pre extraction)?

Answer 30

→ Differential lysis of mammalian cells - bacteria have different cell walls
→ put reagents to lyse the mammalian cells but not bacteria

Question 31

Why can there be a bias with lysing mammalian cells?

Answer 31

→ Bias towards gram +ve bacteria which have a thicker cell wall

Question 32

How do you enrich without amplificaiton (post extraction)?

Answer 32

→ Enzymatic degradation of methylated nucleotides which target mammalian DNA
→ bias against AT rich bacterial genomes