Bacteria in the gut and fermentation

[MRR]

Hello,

I am in high school and I am writing an essay for a competition about microbes inside humans. However, I am very confused about several topics that I have read about, so I would greatly appreciate it if you could answer the following questions!

- What's the difference between glycans and carbohydrates? Do they get digested in the same way in the large intestine?

- many sites state that the methanogens in the gut are anaerobic, so is there no oxygen in the gut?

- is the bacteria B infantis a fermentative bacteria?

- How do fermentative bacteria release hydrogen during fermentation? Why do they produce hydrogen (what benefit)?

- Why do methanogens then reduce carbon compounds using hydrogen to make methane? What is the benefit of that to humans?

- Many sources state that methylotrophic bacteria in the gut produce methane by using carbon sources like acetate and carbon dioxide - how does this work? I thought that methylotrophic bacteria use hydrogen to reduce methanol, so where do acetate and CO2 come into the process? It would help a lot if you could show me the equation that methylotrophic bacteria undergo to 'convert' hydrogen to methane and other products.

Thank you!

[CharonY]

- carbohydrate is a broader term and glycans are a form of carbohydrate. 

-  a significant part of the gut are low are devoid of oxygen. Even in areas that are somewhat oxygenated it is often consumed fairly quickly.

- I assume you mean Bifidobacterium infantis? Yes they can ferment. That is a slightly difficult topic, but I would advise you to think about the function of fermentation (with a special focus of regeneration of NAD+).

- fermentation is not necessarily linked to hydrogen production. Bifodobacterium is mostly known for lactic acid fermentation, for example.

- I think you may be a bit confused regarding methanogens and methylotrophs. Perhaps it would help if you explain what you know of each group and how you think what the respective pathways are.

 

 

[MRR]

19 hours ago, CharonY said:

- carbohydrate is a broader term and glycans are a form of carbohydrate. 

-  a significant part of the gut are low are devoid of oxygen. Even in areas that are somewhat oxygenated it is often consumed fairly quickly.

- I assume you mean Bifidobacterium infantis? Yes they can ferment. That is a slightly difficult topic, but I would advise you to think about the function of fermentation (with a special focus of regeneration of NAD+).

- fermentation is not necessarily linked to hydrogen production. Bifodobacterium is mostly known for lactic acid fermentation, for example.

- I think you may be a bit confused regarding methanogens and methylotrophs. Perhaps it would help if you explain what you know of each group and how you think what the respective pathways are.

 

 

Thanks for the reply. For your last answer, I'll just say that from what i've looked up so far (though it's been hard with several articles contradicting eachother), i've gathered that most methanogens are archaea that generate methane, and that in the gut they can be grouped into two categories depending on what pathway of methanogenesis they take: the methylotrophic pathway and the hydrogenotrophic pathway. I understand the hydrogenotrophic pathway, but i don't understand what happens in the methylotrophic pathway for archaea in the gut. The 'Methanosphaera stadtmanae'  section of this site http://bugs-in-your-guts.com/?p=290#Gaci  states that It' only produces CH₄ by reducing methanol (derived from microbial degradation of pectin) in the presence of H₂, and needs acetate (CH₃COOH) and CO₂ as carbon sources', but how exactly does this reaction occur, and how does acetate and CO2 come into the equation? The source that it referenced did not help with my understanding.

[CharonY]

OK, this is quite a bit more difficult and actually quite advanced. I can only give a short answer which hopefully is not incorrect as I have to go from memory quite a bit, which is basically over ten years old at this point and may be out of date for the particular bacterium. What you need to distinguish are carbon assimilation processes (i.e. ways to get C into the cell to create biomass) and energy conservation/production processes, which generate energy (or allow energy production processes to work). I often found that even college students sometimes get confused at this step as there are some overlaps. Specifically fermentation, is a process that allows regeneration of NAD+, so that energy generating processes (such as glycolysis, which is also part of carbon metabolism) can occur. Now starting from the bottom, Methanosphaera (just as a reminder, genus and species are italicized by convention), utilizes acetate as a carbon source by converting it into acetyl-CoA and subsequently pyruvate. The second step, the conversion of Acetyl-coA is where CO2 is consumed (Acetyl-coA + CO2 + Fd_(reduced) + H+ -> pyruvate + coA + Fd_(ox)

Now the important step here is that methanogenesis is not part of this particular pathway, and that its main purpose is carbon assimilation in the form of acetate. Methanognesis is part of the energy generation process, via oxidation of methanol which goes over several steps from methanol -> CH3-S-coM and from there (again multistep) addition of hydrogen to CH4. While we could discuss details of it, the key is that these are technically two processes. Where there are linked, however is the CH3-S-coM, as the carbon there is derived via multisteps from the pyruvate formed earlier by acetate assimiliation.