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Health News Archive 317 - Colon Health
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Human Intestine Contains 100 Trillion Bacteria

Inside each of us is a vast ecosystem, as complex as the soil or the oceans, that helps us digest food and contributes to our health and well-being.  Gene experts after studying the DNA of hundreds of different kinds of bacteria in the human intestines have reached the conclusion that the human race survives, even thrives, with the help of millions of bacteria within our bodies.

Reporting in Science, researchers say that the thriving microbiologic community in adults consists of up to 100 trillion bacteria, representing more than 1,000 different species, and include more than 60,000 distinct genes - twice as many as in the human genome. The team believe their findings suggest that studying bacteria native to our bodies may provide important clues to disease, nutrition, obesity and how well drugs will work in individuals.

Scientists from the Institute for Genomic Research in Maryland say that because bacteria are so important to key functions such as digestion and the immune system that we may be in fact be symbiotic organisms - relying on one another for life itself.  This microbial population is what dictates our well-being and any change or shift within this population which may lead to the absence or presence of beneficial microbes, can trigger defects in metabolism and the development of diseases such as inflammatory bowel disease.

Scientists have known for some time that at least 50 percent of human feces, and often more, is made up of bacteria from the gut. The researchers say the body is a mixture of bacteria and human cells and some scientists believe as many as 90 percent of the cells on our body are actually bacteria.

The microbial elements help humans to digest much of what they eat, including some vitamins, sugars, and fiber and also synthesize vitamins that humans cannot.  Researchers say humans have evolved for million of years with these bacteria and they provide essential functions.

Microbiologist Steven R. Gill and his team sequenced the DNA in feces donated by two healthy adults who had not taken antibiotics for a year, as these drugs are known to disturb the bacteria in the body. These two subjects were one male and one female; one was a vegetarian.

By comparing the gene sequences to those from known bacteria and to the human genome they found the so-called colon microbiome, the entire sum of genetic material from microbes in the lower gut which includes more than 60,000 genes, which is twice as many as found in the human genome.  Gill said of all the DNA sequences in the material, only one to five percent of it was not bacterial.

They also found a surprising number of Archaea, also known as archaebacteria, which are genetically distinct from bacteria but which are also one-celled organisms often found in extreme environments such as hot springs.  Gill and his team now plan to make a comparison of the gut bacteria in people from different ethnic backgrounds, different diets, drinkers and smokers in order to see if there are distinct differences.

They believe the bacteria help break down the drugs that people take and studying the effects of different populations of the microbes might provide clues to treating different people with various medications.

Gill says the next study will focus on the bacteria in the mouth, of which there are at least 800 species.  Imagine the results when scientists progress to studying the effect of toxins such as carbonic acid (from soda), antibiotics in the food supply, artificial sweeteners, plastic residue and other contaminants on the beneficial bacteria in our intestines.

The research is published in the June 2006 issue of the journal Science.  Researchers collaborated from The Institute for Genomic Research, Stanford University School of Medicine, Department of Microbiology and Immunology, Stanford University, Veterans Affairs Palo Alto Health Care System, Center for Genome Sciences, Washington University School of Medicine, and George Washington University School of Medicine.

Abstract

The human intestinal microbiota is composed of 1013 to 1014 microorganisms whose collective genome ("microbiome") contains at least 100 times as many genes as our own genome. We analyzed 78 million base pairs of unique DNA sequence and 2062 polymerase chain reaction–amplified 16S ribosomal DNA sequences obtained from the fecal DNAs of two healthy adults. Using metabolic function analyses of identified genes, we compared our human genome with the average content of previously sequenced microbial genomes. Our microbiome has significantly enriched metabolism of glycans, amino acids, and xenobiotics; methanogenesis; and 2-methyl-D-erythritol 4-phosphate pathway–mediated biosynthesis of vitamins and isoprenoids. Thus, humans are superorganisms whose metabolism represents an amalgamation of microbial and human attributes.

Source

Steven R. Gill, Mihai Pop, Robert T. DeBoy, Paul B. Eckburg, Peter J. Turnbaugh, Buck S. Samuel, Jeffrey I. Gordon, David A. Relman, Claire M. Fraser-Liggett, Karen E. Nelson. Metagenomic Analysis of the Human Distal Gut Microbiome. Science 2 June 2006: Vol. 312. no. 5778, pp. 1355 - 1359. DOI: 10.1126/science.1124234

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