Bacterial cells in the body outnumber human cells by a factor of 10 to 1. Yet only recently have researchers begun to elucidate the beneficial roles these microbes play in fostering health. Some of these bacteria possess genes that encode for beneficial compounds that the body cannot make on its own. Other bacteria seem to train the body not to overreact to outside threats. Advances in computing and gene sequencing are allowing researchers to create a detailed catalogue of all the bacterial genes that make up this so-called microbiome. Unfortunately, the inadvertent destruction of beneficial microbes by the use of antibiotics, among other things, may be leading to an increase in autoimmune disorders and obesity. Biologists once thought that human beings were physiological islands, entirely capable of regulating their own internal workings. Our bodies made all the enzymes needed for breaking down food and using its nutrients to power and repair our tissues and organs. Signals from our own tissues dictated body states such as hunger or satiety. The specialised cells of our immune system taught themselves how to recognise and attack dangerous microbespathogenswhile at the same time sparing our own tissues. However, over the past decade or so, researchers have demonstrated that the human body is not such a neatly self-sufficient island after all. It is more like a complex ecosystema social networkcontaining trillions of bacteria and other microorganisms that inhabit our skin, genital areas, mouth and especially intestines. In fact, most of the cells in the human body are not human at all. Bacterial cells in the human body outnumber human cells 10 to one. Moreover, this mixed community of microbial cells and the genes they contain, collectively known as the microbiome, does not threaten us but offers vital help with basic physiological processesfrom digestion to growth to self-defence.
Scientific American, 15 May 2012 ;http://www.sciam.com ;