A4 - Microbiota of the Gut

What are some examples of diseases an imbalance in the gut microbiota can cause?

• Inflammatory bowel disease

• Obesity

• Diabetes

• Heart/Kidney/Liver diseases

What did the initial human microbiome project study use?

Initially used 16S rRNA and metagenomic sequencing

The human microbiome project found the gut was mainly inhabited by four bacterial phyla. What are these four phyla?

Bacteroidetes (Bacteroidota)

Firmicutes (Bacillota)

Actinobacteria

Proteobacteria

Are Bacteroidetes gram negative or gram positive?

Gram negative

Are Firmicutes gram negative or gram positive?

Gram positive

Are Actinobacteria gram negative or gram positive?

Gram positive

Are Proteobacteria gram negative or gram positive?

Gram negative

True or false?

Firmicutes are very diverse with numerous species present 

True.

Firmicutes are very diverse with numerous species present 

True or False?

Bacteroidetes are very diverse with many species being present.

False.

Bacteroidetes are less diverse with most being Bacteroides. Spp 

What were the three main findings of the human microbiome project?

Each individual has 100-150 different species present

Microbiotas are largely different between individuals

Does not appear to be a ‘keystone’ group of essential species which are shared by everyone

True or False.

There is no ‘keystone’ group of essential bacteria species shared by everyone and so metabolic pathways also vary massively between individuals.

False.

Even if people have different species of bacteria, the metabolic pathways which occur are consistent across individuals 

How does Bacteroides thetaiotaomicron (Bt) induce fucosylation of glycans on mice intestinal enterocytes?

Bt uses a Fuc locus which produces a fucosylation signal which host cells respond to

FucR acts as a repressor of which locus?

Fuc locus in Bacteroides thetaiotaomicron (Bt)

Fill in the blanks.

When no fucose is present FucR ______ DNA which prevents fucose utilization signals

When no fucose is present, FucR binds to DNA which prevents fucose utilization signals

Fill in the blank.

When fucose is present, FucR _____ DNA which prevents signalling for host fucosylation

When fucose is present, FucR binds to DNA which prevents signalling for host fucosylation

SCFAs are recognised by what receptor on Treg cells?

GPR43 receptors on Treg cells.

What does binding of SCFAs to GPR43 on Treg cells cause?

• Induces IL-10 production (Anti-inflammatory)

• Blocks inflammation pathways

• Allows colonization of the gut by the microbiota

How are pathogens recognised in the gut?

Pathogens produce Pathogen Associated Molecular Patterns (PAMPs) which are recognised by immune cells and triggers an immune response

How are beneficial bacteria protected from the immune system?

Beneficial bacteria produce specific molecules which module the immune system and prevent it from killing the beneficial bacteria

Bacteroidetes Fragilis produces what molecule to modulate the immune system?

Polysaccharide A (PSA)

Bacteroidetes Fragilis produces Polysaccharide A (PSA). What does PSA do?

PSA is recognised by innate immune cells via Toll-like receptor 2 (TLR2).

• This leads to induction of Treg cells and production of IL-10

What is unexpected about PSA binding to TLR2 to downregulate an immune response?

TLR2 is usually associated with immune activation and not immune suppression.

What is special about the Bacteroidetes Fragilis’ Polysaccharide A (PSA) molecule?

Zwitterionic polysaccharide (+ve and -ve charge)

• Very few bacteria species produce molecules like this

The gut immune cells produce intestinal complement (C3). How does this target only pathogenic bacteria?

C3 complement specifically targets bacteria by phagocytosis only

• Membrane Attack Complex cannot be formed.

This means only pathogenic bacteria will be killed and commensal bacteria will be ignored.