Introduction
Trillions of microbes constitute the “Metagenome” of the human gut. This is the organ called microbiome, which is highly essential, and offers the host benefits such as metabolic abilities, pathogen protection, immune system enhancement, and GI tract developmental modulations (De Fillipo, et al.).
In their study, three questions regarding the evolution of the human microbiota have been raised. They are: (1) how does the partitioning of bacterial diversity between and within two populations studied? (2) Does there exist a correlation between the diet and bacterial diversity?; and (3) considering the varied geography and hygienic conditions, what is the bacterial pathogen distribution in the two populations?
The main reasons for probing or delving into these questions are to prove that the human microbiota is indeed influenced by the dietary patterns and is independent of ethnicity and environment.
Results and Discussion
Dietary Habits of the Two Samples of Children
In their study, the authors characterized the microbiota in the feces of fourteen children from the ethic group of Mossi (BF). These children lived in the Boulpon village in Burkina Faso, and were regarded as representatives of the real African diet. Predominantly vegetarian foods that were low in animal protein, but high in plant polysaccharides, fiber, and starch were characteristically fed to these BF children of Africa. The diets comprised majorly legumes, cereals, and vegetables, and, hence, were rich in fiber and carbohydrates with very little animal protein. Rarely, these children consumed small amounts of chicken.
Representing the Western population in Europe were children of the same ages as their African counterparts, but eating a diet and thriving in an environment characteristic of the developed world. These children were found consuming diets higher in animal protein, starch, and sugar and fat, and that which was low in fiber. BF children of ages 1-2 years old consumed 1,068.7 kcal/d, while children of Europe of the same ages consumed 1,512.7 kcal/d.
Bacteroidetes Dominate the Microbiota of BF samples Compared with EU Children
When multiplex pyrosequencing of the 16S SRNa gene’s V5 and V6 hyper-variable regions was performed, it was found that in 94.2% of the sequences from both the EU and BF samples constituted the Actinobacteria, Firmicutes, Bacteroidetes, and Proteobacteria species. This was in agreement with previous studies that pointed out that these were the phyla contributing to the major portions of the micobiota in the human gut.
However, there were marked differences in the proportions of the 4 phyla present in the microbiota of the EU and BF samples. Bacteroidetes and Actinobacteria were present in greater amounts in BF samples as compared to European samples, while Proteobacteria and Firmicutes were present in abundance in EU samples than in BF samples.
The microbiota is shaped to a major extent by diets. It has been found that the ratio of Firmicutes to that of Bacteroidetes is different in obese and lean humans. The proportion is lower, consistent with weight loss and those on a low-calorie diet (Ley et al.). Thus, the increase in the ratio of F/B in EU children is backed by their high calorie diets, and this typical ratio may predispose them to further obesity in the future. Thus, the F/B ration may well be considered an obesity biomarker.
As soon as breast feeding is stopped, and the ingestion of solid foods takes place, the two populations start differing in their microbiota (Mariat et al.). This shows that the F/B ratio depends on diets and environments. Therefore, due to these differences, the BF population was found to have more Gram negative bacteria than the Gram positive ones. The converse was true in the EU samples, with Gram positive bacteria namely Firmicutes dominating.
A high fiber diet could bring about positive changes in gut microbiota, increasing the numbers of beneficial bacteria and thus, enriching the microbiome. Non-infectious intestinal disorders are a common sight now amongst the western people and developed world as they feed on high proteins, sugars and fats and low unabsorbable fibers. Burkett described the positive effects of a vegetarian diet on bowel disorders. He observed the absence of noninfectious colon disease sin African communities consuming high-fiber diets.
Whole grains constitute resistant starch, dietary fiber, and ologoscahhrides that escape small intestine digestion, but get fermented in the gut to form short chain fatty acids (SCFAs). Xylanibacter, Butyrivibrio, Prevotella, and Treponema present exclusively in the BF children show that the bacterial community present in this microbiota use xylenes, xylose, and carboxymethylcellulose to form high levels of SCFAs (Flint). SCFAs play a major role against gut inflammation.
The richness of the gut microbiota can have several effects on health. The bacteria producing SCFAs in the BF children help to inhibit the establishment of pathogenic intestinal microorganisms that cause diarrhea. Thus, the “old friend” hypotheses are true when the BF children are considered as the rich microbiota protect them against GI tract diseases as well as pathogens.
Thus, the results are consistent with the findings of other studies showing that gut micro biomes of urban people are different from traditional people. Obregon-Tito et al., characterized the fecal samples of hunter-gatherers and urban community people from Peru and an industrialized community from the US. It was found that the Treponema sp. is found in the gut micorbiomes of traditional peoples. These Treponema sp. were similar to the Treponema succinifaciens of swine and fell out of the range of pathogenic classes. Gut Treponema was found in traditional people and non-human primates studied up to date thus, shedding light on the fact that they are symbionts who have vanished from urban and industrialized societies.
Yatsunenko et al., observed pronounced differences in assemblages of bacteria and “functional gene repertoires” between the American residents and those from Venezuela and rural Malawi.
According to Schnorr et al., the human gut microbiota changes with respect to lifestyle. To understand this, the authors studied the phylogenetic diversity and production of metabolites in the gut microbiota from the Hadza community of Tanzania, who were hunter-gatherers. It was found that the richness of microbiota was higher in the Hazda community than in the Italian urban dwellers.
Material and Methods
A total of 15 children were enrolled, who lived in Boulpon village of Burkina Faso, and 15 other children who were the western counterparts from Florence, Italy participated in the study. All children war from 1-6 years of age and had not been on antibiotics in the 6 months before sampling. The BF children’s mothers were interviewed on their diets directly, and a detailed medial and lifestyle report obtained from the EU children’s parents.
For each sample, the 16S rRNA genes were amplified useing primer sets for the V5 and V6 hypervariable regions. The sequences were classified according to taxonomy using the RDP classifier. The ANOVA and Kruskal-Wallis test were employed to study the differences between the two populations The Mothur software packages were used to obtain the richness and biodiversity indices. For richness estimates, the Chao 1 index was used. The nonparametric Shannon formula was used to determine the biodiversity of samples. About 250mg of frozen fecal samples from both populations were used for 16S rRNA determination.
Conclusion
The results derived from this study show that the diet has a role that predominantly affects the gut microbiota as compared to factors such as sanitation, hygiene, climate, and geography and ethnicity. The adaptive potential of the microbiome is limited in industrialized countries as there is predominant consumption of high calorie, fat and sugar-rich diets as compared to their African counterparts.
Work Cited
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De Fillipo, C., et al., “Impact Of Diet In Shaping Gut Microbiota Revealed By A Comparative Study In Children From Europe And Rural Africa,” Proc Natl Acad Sci U S A., 107.33(2010): 14691–14696.
Flint, H. J., et al., “Polysaccharide Utilization By Gut Bacteria: Potential For New Insights From Genomic Analysis,” Nat Rev Microbiol. 6.2(2008):121-131.
Ley, R. E., et al., “Microbial Ecology: Human Gut Microbes Associated With Obesity.” Nature., 444.7122(2006):1022-1023.
Mariat, D., et al., “The Firmicutes/Bacteroidetes Ratio Of The Human Microbiota Changes With Age”, BMC Microbiol., 9(2009):123.
Obregon-Tito et al., “Subsistence Strategies In Traditional Societies Distinguish Gut Microbiomes,” Nature Communications, 2015.
Schnorr, S., L., et al., “Gut Microbiome Of The Hadza Hunter-Gatherers,” Nature Communications, 2014.
Yatsunenko, T. et al., “Human Gut Microbiome Viewed Across Age and Geography,” Nature. 486.7402(2012):222-227.
