A6 - Glycan metabolism by the Microbiota II

Which type of bacteria use Sus-like systems to metabolise glycans?

Bacteroidetes

Which type of bacteria use ABC transporters and cell wall anchored enzymes to metabolise glycans?

Firmicutes

What are CMBs?

Carbohydrate binding molecules

How do Firmicutes break down and absorb glycans?

Glycans bind to CMBs and cell wall anchored Glycoside hydrolases break them down

ABC transporter is then used to transport broken down glycans into the cytoplasm

What is the evidence that Firmicutes and Bacteroidetes may target different forms of glycan?

Faecal particles are primarily colonised by firmicutes

• (insoluble polysaccharides)

Some Bacteroidetes seem to partition more into the liquid phase instead

• (soluble fibre particles)

Bifidobacteria belong to the phyla _____ and are gram ______.

Belong to the phyla Actinobacteria and are gram positive.

Actinobacteria use a similar apparatus to _______ to metabolise glycans.

• They use _________

Actinobacteria use a similar apparatus to Firmicutes to metabolise glycans.

• They use ABC transporters and surface GHs

Both Actinobacteria and Firmicutes use cell surface GH enzymes but Actinobacteria enzymes are less complex than Firmicutes and are missing something.

What are they missing?

Actinobacteria enzymes have no Carbohydrate Binding Modules (CMBs)

When is Bif. Adolescentis able to use simple xylans and why?

Only when it is in co-culture with B. ovatus.

• This is because B. ovatus can break down simple xylans and some oligosaccharides are lost during this

• These oligosaccharides can then be used by B. Adolescentis

Why is B. Adolescentis unable to use complex xylans even when in co-culture with other bacteria?

The breakdown products of complex xylans are too complex for B. Adolescentis.

Pre-weaning, the infant gut is dominated by which bacteria species?

Dominated by Bifidobacterium. spp

What does human milk contain which promotes high levels of Bifidobacterium growth?

Human milk contains a large number of Human Milk Oligosaccharides (HMOs) which Biffidobacteria are very good at using.

Other bacteria can also use Human Milk Oligosaccharides (HMOs) so why are Biffidobacterium able to dominate and not other bacteria?

Biffidobacteria have a preference for a common specific HMO called Lacto-N-neoteraose (LNnT)

• This allows them to out perform other bacteria

Long term low fibre diet leads to loss of diversity. Switching back to a high fibre diet still shows decreased diversity after recovery. Why?

Suggests long term low fibre diet causes extinction of some microbial species. This means even switching diet will not bring them back

What is the main evidence for the role of fibre in humans?

Analysis of microbiota from people from ‘traditional’ non-industrial societies

These societies have much higher microbiota diversity and almost no chronic diseases like IBD/CRC

• People who move to western countries have higher incidence of IBD and CRC

Seems to suggest that more diversity = a more resilient ecosystem