Life in our digestive track
Gut flora & the intestinal microbiome
What is gut flora?
[Image: 4 different Yakult flavors in Singapore. Yakult is a popular probiotic meant to stimulate the presence of Lactobacillus in the human colon.]
Case study: E. Coli
The often-studied lac operon was first discovered in E. Coli, and serves as the primary mechanism for lactose fermentation in the bacteria - since E. Coli can take up and digest excess lactose, it can alleviate the effects of lactose intolerance in humans. In the vast majority of cases, E. Coli is either harmless or beneficial to us, driving out pathogenic bacteria through competition or synthesizing vitamin K. However, particular strains can cause severe food poisoning or even death. Food contaminated with E. Coli is generally recalled.
Why does it matter?
Effects on human biology
95% of Serotonin in the human body is produced in the colon. Serotonin is a crucial neurotransmitter involved in everything from
Waking cortisol levels are lower in experimental subjects taking β-Galacto-Oligosaccharide, a probiotic. High levels of
Lactobacillus johnsonii is correlated with a longer lifespan and lower disease penetration in mice predisposed to lymphoma.
Microbiota can prevent infection of the gut by pathogenic bacteria through competitive inhibition. (ex: Clostridium Dificille infection, an antibiotic-resistant bacteria which can lead to severe bloating and even death, typically follows intensive antibiotic treatment which decreases the amount and variety of normal gut bacteria).
- Firmicutes are positively correlated with obesity. However, knowing that intestinal bacteria concentrations are affected by diet, it could be that high-fat diets lead to Firmucutes colonization. It is also possible that a genetic predisposition to obesity also leads to high levels of the bacteria.
[Image: Lactobacillus Johnsonii]
Nature or nurture?
There is evidence of differences in gut flora in people with diabetes I, II, and certain genetic cancers. However, the difference in gut flora in people with diabetes might be a result of the dietary restrictions recommended for people with diabetes.
Gut flora distributions are, in part, genetically coded. This leads to two possibilities:
A particular gene leads to a predisposition to diabetes II, which in turn causes the host to restrict their diet, changing gut bacteria concentrations.
A particular gene leads to a difference in gut bacteria, which in turn might cause the host to crave sugary foods (i.e a “sweet tooth”), leading to diabetes II.
There is a current debate involving sterility while in the womb - though traditional medical knowledge indicates that the fetal intestine is completely sterile, and colonization follows exposure to the external environment, current research might indicate that this is not the case, and colonization begins in the womb.
- B. Wadsworthia shows a significant uptick following a diet heavy in animal products, and is also positively correlated to obesity. This suggests that nurture, not nature, determines our gut flora.
Intestinal bacteria modify lymphoma incidence and latency by affecting systemic inflammatory state, oxidative stress, and leukocyte genotoxicity
Westbrook A.M., Wei B., Loy A., Chang C., Braun J., Borneman J., Schiestl R.H., (...), Reliene R. (2013) Cancer Research, 73 (14) , pp. 4222-4232.
Cénit, M., Matzaraki, V., Tigchelaar, E., & Zhernakova, A. (2014). Rapidly expanding knowledge on the role of the gut microbiome in health and disease. Biochimica Et Biophysica Acta (BBA) - Molecular Basis of Disease,1842(10), 1981-1992. Retrieved February 9, 2016.
Feltman, R. (2013, December 14). Scientific American. Scientific American.
Cross, K. (n.d.). Lactobacillus johnsonii (smooth mutant) [Photograph]
Todar, K. Pathogenic E. coli. Online Textbook of Bacteriology. University of Wisconsin–Madison Department of Bacteriology. Retrieved 2007-11-30
Dezzawong. (2009, October 31). SG Yakult 4 Flavours. [Photograph]