Link Between Microbes and Obesity

Introduction

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Introduce the topic of your paper. What microorganisms are of interest? Habitat? Applications for medicine and/or environment?

Gut Microbiota

The role of the gut microbiome is the focus of renewed interest in health and disease. There has been an increasing number of scientific articles published on intestinal microbiota each year over the past several decades. Most studies were devoted to understanding the impact in the intestinal environment, however, new studies are looking at the effect of commensal microbes on the mammalian gut. The human gut microbiota is composed of microorganisms that live in the digestive tract and is considered the largest supply of the human flora. The composition of the human gut microbial community is host specific. The microbial community is continually evolving due to exogenous and endogenous modifications. The microbiota can be at the center of causing many diseases which can have serious effects on all organ systems in the body. The compositional make-up of the microorganisms in the human gut is an important determinant of maintaining homeostasis or not.

The human body serves as beneficial host for many microorganisms including: bacteria, archaea, viruses, and unicellular eukaryotes. The microbiota refers to the group of microorganisms living in peaceful coexistence within their host. The human microbiota holds as many as 10¹⁴ bacterial cells. The human gut, a very large organ, has the surface size of approximately 200 m². Therefore, the human gut is an important surface for microbial colonization, along with GIT which is rich in microbial nutrients.

The gut microbiota is mostly composed of strict anaerobes; 99% of the bacteria in the gut are anaerobes. Two bacterial phyla, Bacteroidetes and Firmicutes, are the most predominant in the human gut. The following bacterial phyla: proteobacteria, verrucomicrobia, actinobacteria, fusobacteria, and cyanobacteria also have a smaller presence in the gut microbiota. The human gut microbiota can contain approximately 500 to 1,000 species and the collective human gut microbiota is composed of over 35,000 bacterial species. The intestinal microbiota is not homogeneous; the number of bacterial cells increases as it moves through the GI tract. 10¹ to 10³ bacteria per gram are present in the stomach and duodenum. The number of bacteria per gram increases to 10¹² in the colon, which is the final location of the GI tract. Different bacterial groups thrive at each different site in the intestine. For example, Bacteroides are found only in feces whereas Clostridium, Lactobacillus, and Enterococcus were found only in the mucus layer of the small intestine. The presence of colonized microbes in the human gut occurs immediately at birth. During the first year of life, the gut microbiota varies from human to human. However, after one year of age, the gut microbiota stabilizes and colonizes.

There are many contributing factors to the composition of the gut microbiota. Gut microbial composition can depend on host genetics, mutations, and diet based on studies of obesity.

Human gut-microbe populations fall into three distinct categories. The three categories are named after the dominant genus: Bacteroides, Prevotella, and Ruminococcus. Bacteroides are known for being able to break down carbohydrates. Prebotella are known for degrading the slimy mucus in the gut and will therefore lead to increased gut pain. Ruminococcus is commonly associated with weight gain because it helps cells absorb sugar. This revelation can help identify the causes of obesity and inflammatory bowel disease. The identification of a person’s gut type makes it possible for a person to determine what they can eat to stay slim and how well they metabolize.

Obesity

Obesity is the leading preventable cause of death worldwide. Obesity is a medical condition that affects 35.9% of the American population 20 years and older. Excess body fat accumulates and leads to adverse effects on health which can lead to a reduced life expectancy and increase health problems. An person is considered obese when their BMI, body mass index, exceeds 30 kg/m². Body mass index is determined by dividing a person’s weight in kilograms by the person’s height squared. Obesity increases the likelihood of the following diseases: heart disease, type 2 diabetes, obstructive sleep apnea, and osteoarthritis. Obesity occurs when a person consumes more calories than he or she burns. Therefore, the most common cause is a person eating too much and exercising too little. Other factors that play a role in obesity are: age, gender, genetics, environmental factors, physical activity, psychological factors, illness, and medication. Treatment options for obesity include dieting, physical exercise, and gastric bypass surgery. It is important to understand the mechanisms behind obesity and look to the correlation between the gut microbiota and obesity. Obese individuals tend to have a makeup of pathogens in their intestine that is different from that of people who are of normal weight.

Conclusion

This new field has shown the link between obesity and microorganisms living in the gut. Many current studies have shown how certain bacteria are responsible for an increase in weight. These studies are revolutionary because they show the importance of genetic and biotic factors that might be responsible for changes in weight. This new field can lead to new treatments on how to alter the gut microbiota to manage changes in weight.

References

1.Arumugam, M. et al. Nature Advance online publication doi:10.1038/nature09944 (2011)
2.Benson A et al. (2010) Individuality in gut microbiota composition is a complex polygenic trait shaped by multiple environmental and host genetic factors. October 11, 2010, doi:10.1073/pnas.1007028107 PNAS November 2, 2010 vol. 107no. 44 18933-18938
3.Chierico et al. (2012)Early-life gut microbiota under physiological and pathological conditions: The central role of combined meta-omics-based approaches. Journal of Proteomics Volume 75, Issue 15, 3 August 2012, Pages 4580–4587
4.CDC. Obesity and Overweight. 2013.
5.Sekirov I, Russell S, Caetano L, Antunes M, Finlay B. (2010) Gut Microbiota in Health and Disease. doi: 10. 1152/ physrev. 00045. 2009 Physiol Rev July 1, 2010 vol. 90no. 3 859-904

Edited by student of Joan Slonczewski for BIOL 238 Microbiology, 2011, Kenyon College.