Download CSIRO_The Hungry Microbiome Project_Starch

CSIRO_The Hungry Microbiome Project_Starch Fermentation-SD
[Image shows a person’s hand writing on a whiteboard and text appears: The Hungry Microbiome. A diagram is drawn
beneath the title]
Narrator: This is Ormando(?). This video was created as part of the Hungry Microbiome Project, which I made at
CSIRO.
[Image shows a person’s hand writing on a whiteboard and text appears: The Hungry Microbiome. A diagram is drawn
beneath the title]
This is Ormando(?). This video was created as part of the Hungry Microbiome Project, which I made at CSIRO.
[Image changes to show a person’s hand drawing a diagram on a whiteboard and text appears: Food “Starch”; small
intestine; large intestine “colon”; resistant starch]
Some foods are not digested and absorbed by the small intestine and so reach the large intestine, also known as the
colon. Resistant starch, for example, is a portion of starch that escapes digestion in the small intestine because it is
resistant to human digestive enzymes. However resistant starch still contain energy that our body needs, and so once
resistant starch reaches the colon the resistant starch will undergo fermentation by the trillions of bacteria that live
there.
[Image changes to show a person’s hand drawing on the diagram and text appears: Resistant starch; bacteria]
Through fermentation the bacteria produces substances such as short chain fatty-acids, which our colon cells use as
their main source of energy.
[Image changes to show a person’s hand drawing on the diagram and text appears: Short chain fatty-acids]
[Image changes to show a person’s hand writing on a whiteboard and text appears: Starch Fermentation]
In this video we will focus on the process of starch fermentation. Starch that has resisted digestion in the small
intestine and reached the colon are called resistant starch.
[Image changes to show a person’s hand drawing a diagram on a whiteboard and text appears: Resistant starch]
Resistant starch will undergo fermentation by bacteria in the colon.
[Image changes to show a person’s hand drawing on the diagram and text appears: Amylose and amylopectin;
Glucose]
Resistant starch are made up of amylose and amylopectin, which are two forms of glucose polymers. Fermentation of
carbohydrates such as resistant starch lead to the production of short chain fatty-acids.
[Image changes to show a person’s hand drawing on the diagram and text appears: Fermentation of carbohydrates
lead to the synthesis of short chain fatty-acids]
Let us look at a simple pathway of how these short chain fatty-acids are produced.
[Image changes to show a person’s hand drawing on the diagram and text appears: Primary degraders;
bifidobacterium spp.; bacteroides spp.; ruminococcus bromii]
Now within the colon you have primary degraders of resistant starch, such as bifidobacterium species, bacteroides
species and ruminococcus bromii. The primary degraders have enzymes that are important in breaking down resistant
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starch and fermenting it. Many products are produced through the fermentation of resistant starch by the primary
degraders.
[Image changes to show a person’s hand drawing on the diagram and text appears: Glucose]
Glucose can be released thanks to membrane bound enzymes that cleave off glucose polymers. Through
fermentation of glucose these primary degraders can produce the two carbon short chain fatty-acid acetate, and
release formate in the process.
[Image changes to show a person’s hand drawing on the diagram and text appears: Acetate; Formate (CO2, H2)]
Formate is essentially gases, carbon dioxide and hydrogen. These can later be used by other bacterial species that live
in the colon. Through the fermentation of glucose the primary degraders can also produce the three carbon short
chain fatty-acid called propionate, which also forms some gases as a by-product.
[Image changes to show a person’s hand drawing on the diagram and text appears: Propionate]
[Image changes to show a person’s hand drawing on the diagram and text appears: Succinate and lactate are also
produced and are efficiently utilised by certain anaerobic bacteria]
Now succinate and lactate are also produced by these primary degraders, and are efficiently utilised by certain
anaerobic bacteria. The gases formed through fermentation, such as formate, can be utilised by methanogens to
produce methane.
[Image changes to show a person’s hand drawing on the diagram and text appears: Formate (CO2, H2) – methanogens
- CHG]
Interesting fact, methane and other gases, such as carbon dioxide and hydrogen, contribute to the chemistry of fart
and its smell. Because these gases are produced in the lumen of the colon they are often expelled out. Also if there is
sufficient amounts of formate acetogens are able to utilise formate to produce acetate.
[Image changes to show a person’s hand drawing on the diagram and text appears: Acetogens – Acetate]
Now back to the degraders. There are another set of bacteria called the secondary degraders that also contribute to
the fermentation of resistant starch.
[Image changes to show a person’s hand drawing on the diagram and text appears: Secondary degraders]
However the secondary degraders are considered to have no enzymes that initiate the cleavage of glucose from the
glucose polymers that make up resistant starch, and so the secondary degraders, such as the firmicutes species, rely
on the primary degraders to release glucose monomers.
[Image changes to show a person’s hand drawing on the diagram and text appears: Firmicutes spp.]
The firmicutes species can utilise the glucose and ferment it, to produce a four carbon short chain fatty-acid called
butyrate.
[Image changes to show a person’s hand drawing on the diagram and text appears: Butyrate]
Some of the secondary degraders can also utilise acetate to produce butyrate as an end product.
[Image changes to show a person’s hand indicating on the diagram]
So through the fermentation of starch acetate, propionate and butyrate are the main short chain fatty-acids
produced, normally in a 3:1:1 ratio, so more acetate being produced.
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[Image changes to show a person’s hand drawing on the diagram and text appears: Acetate, propionate and butyrate
are the main SCFAs produced normally in a ratio of 3:1:1]
At a low pH, about 5.5, butyrate producing bacteria are known to dominate the colon.
[Image changes to show a person’s hand drawing on the diagram and text appears: pH 5.5 butyrate producing
bacteria dominate]
However at a slightly higher pH, about 6.5, acetate and propionate producing bacteria dominate, and butyrate
producing bacteria seem to be less prominent.
[Image changes to show a person’s hand drawing on the diagram and text appears: pH 6.5 acetate and propionate
producing bacteria dominate]
From the lumen these short chain fatty-acids are absorbed by the colon, they’re absorbed by the colon epithelial cells
known simply as colonocytes.
[Image changes to show a person’s hand drawing on the diagram and text appears: Colonocytes]
About 95% of the short chain fatty-acids are rapidly absorbed by the colon cells, while the remaining 5% are excreted
in the faeces.
[Image changes to show a person’s hand drawing on the diagram and text appears: 95% of SCFAs are rapidly
absorbed, while the remaining 5% is excreted in the faeces]
After being absorbed by the colon cells the short chain fatty-acids can enter circulation, and enter the portal vein,
which is blood travelling towards the liver. Here propionate and acetate enter the portal blood.
[Image changes to show a person’s hand drawing on the diagram and text appears: Propionate; Acetate]
Butyrate on the other hand is the major energy source for colon cells, resulting in low concentrations of butyrate in
portal blood.
[Image changes to show a person’s hand drawing on the diagram and text appears: Butyrate is the major energy
source for the colon cells; Butyrate]
Now let’s briefly find out the fates of the short chain fatty-acids. So acetate is the principal short chain fatty-acid in
the colon. It is metabolised in peripheral tissues.
[Image changes to show a person’s hand drawing on the diagram and text appears: The principal SCFA in the colon. It
is metabolised in peripheral tissues]
In the liver acetate has shown to stimulate lipogenesis, the synthesis of fats.
[Image changes to show a person’s hand drawing on the diagram and text appears: Liver – lipogenesis primary
substrate for cholesterol synthesis]
Acetate is also the primary substrate for cholesterol synthesis. Propionate travels to the liver and is used as a
substrate for gluconeogenesis.
[Image changes to show a person’s hand drawing on the diagram and text appears: Liver – propionate is a substrate
for gluconeogenesis]
Butyrate is the preferred fuel for colon cells.
[Image changes to show a person’s hand drawing on the diagram and text appears: Butyrate is the preferred fuel of
the colon cells. Lower amounts in the blood compared to other SCFAs]
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About 75% of energy for colon cells come from butyrate, and because of this there are lower amounts of butyrate in
the blood, compared to the other short chain fatty-acids. In the liver butyrate is oxidised, preventing toxic systemic
concentrations.
[Image changes to show a person’s hand drawing on the diagram and text appears: Liver – Butyrate is oxidised,
preventing toxic systemic concentrations]
And that concludes this video.
[Image changes to show all the diagrams drawn]
We looked at starch fermentation and how fermentation of resistant starch by bacteria produce short chain fattyacids, such as acetate, propionate and butyrate, all of which have many...
Transcribed by: www.transcriberonline.com
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