- De novo synthesis of essential vitamins, which are not producible in host cells.
   + Ex1: Lactic acid bacteria helps synthesize B12 
   + Ex2: In humans, vitamin K, riboflavin, thiamine, etc.
       
- Colonic bacteria metabolizes bile acids to secondary bile acids

University of California, Davis

- Helps maintaining the integrity of mucosal barrier
   
- Provides nutrients

- Protect against pathogens
  


Roles of the Gut Microbiomes

(1) Willey, J.. Prescott's Microbiology. McGraw-Hill Higher Education, 11th ed. (2020), c.34.

(2) Thursby, Elizabeth, and Nathalie Juge. “Introduction to the human gut microbiota.” The Biochemical journal vol. 474,11 1823-1836. 16 May. 2017, doi:10.1042/BCJ20160510

(3) Jessica Cording, M.S. “Want To Avoid Gas & Bloating At Holiday Parties? Don't Eat This Healthy Food.” Mindbodygreen, Mindbodygreen, 29 Sept. 2020,www.mindbodygreen.com/articles/how-cruciferous-vegetables-can-cause-gas-and-bloating . 

(4) John P. Cunha, DO. “Low FODMAP Diet for IBS: List of Foods to Eat and Avoid.” MedicineNet, MedicineNet, 17 Feb. 2021, www.medicinenet.com/low_fodmap_diet_list_of_foods_to_eat_and_avoid/article.htm#:~:text=FODMAPs%20are%20not%20absorbed%20well,Gas. 

(5) Jessica Cording, M.S. et al.  “Want To Avoid Gas &amp; Bloating At Holiday Parties? Don't Eat This Healthy Food.” Mindbodygreen, Mindbodygreen, 29 Sept. 2020, www.mindbodygreen.com/articles/how-cruciferous-vegetables-can-cause-gas-and-bloating. 

(6) Doucleff, Michaeleen. “Chowing down on Meat, Dairy Alters Gut Bacteria a Lot, and Quickly.” NPR, NPR, 11 Dec. 2013, www.npr.org/sections/thesalt/2013/12/10/250007042/chowing-down-on-meat-and-dairy-alters-gut-bacteria-a-lot-and-quickly. 

(7)Villines, Zawn. “The Worst Foods for Gut Health.” Medical News Today, MediLexicon International, 5 Sept. 2019, www.medicalnewstoday.com/articles/326256#:~:text=A%202019%20study%20suggested%20that,of%20heart%20attack%20and%20stroke. 

(8) Ana Maldonado-Contreras Assistant Professor of Microbiology and Physiological Systems. “A Healthy Microbiome Builds a Strong Immune System That Could Help Defeat Covid-19.” The Conversation, 25 May 2021, theconversation.com/a-healthy-microbiome-builds-a-strong-immune-system-that-could-help-defeat-covid-19-145668. 

(9) “How Your Gut Affects Your Immune System: A Symbiotic Relationship.” GilbertLab, 8 June 2021, gilbertlab.com/immune-system/gut-microbiome-symbiosis/.  

(10) Zanteson, Lori. “Gut Health and Immunity - It's All about the Good Bacteria That Can Help Fight Disease.” Today's Dietitian, 2012, www.todaysdietitian.com/newarchives/060112p58.shtml. 


Microbiomes References

- Three predominant SCFAs: propionate, butyrate, acetate in 1:1:3 ratio
- Absorbed by epithelial cells in GI tracts to regulate cellular processes such as gene expression, chemotaxis, apoptosis, etc. 
- Regulate hepatic lipid and glucose homeostasis, inflammatory response 
- Influence the production of cytokines that help maintain and repair the epithelial integrity

Maintain mucosal barrier's integrity

- Interactions with mucosal immune system is important for immune functions
- Compete for attachment sites, nutrient resources and signal the host to excrete antimicrobial substances (AMP, C-type lectin, (pro)defensins, etc.) through their metabolisms
- Inducing mucosal SIgA, which directed againsts gut commensal bacteria, is anchored in the outer layer of colonic mucus to prevent pathogens and maintain beneficial relationships with the commensal
- PRR-MAMP results in actions of multiple signalling pathways to improve the immune system

Protect against Pathogens

[All sources where information was found are cited in MLA format] 

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