With the recognition that our resistance to disease is based on more than just our immune systems and often involves the activity of the many different, usually symbiotic, microorganisms that reside on and within us, increasing research is being focused on determining just what these organisms are and what they do for us. Indeed, it is estimated that for every cell in our body carrying our human genes there are about ten tiny organisms carrying different genomes all living comfortably on our skin, in our various cavities, or within our gut. We know that some of these are vital to our health as they produce some essential vitamins, aid in the digestion of foods, or help fight off invasion by disease producing organisms.
Recently, there has been more effort to identify and characterize some of the trillions of protozoa, bacteria, and viruses that live in our intestines. For instance, it has been found that there can be large differences between the microbes found in the gut of different individuals. In addition to these differences among healthy persons, it has been found that there are often abnormal bacterial communities in the bowels of people with such diseases as inflammatory bowel syndrome, colon cancer, and irritable bowel syndrome. Whether these altered bacterial communities are related to the cause of these illnesses or are an adaptive change in response to these diseases is unknown at present.
One’s genetic constitution does not seem to determine the flora in one’s gut either as even identical twins can have widely different bacterial populations. However, research has shown that if we group our bacterial colonists into genera (and not species) it can be shown that the bulk of the bacteria in humans (including those with bowel disease) can be grouped into three different genera. In this context, a person’s diet does effect the bacterial composition of his or her bowel. In particular, people on a predominately saturated fat and animal protein diet have mostly Bacteroides species, while those consuming a high carbohydrate, predominantly plant-based, diet have bowel bacteria composed largely of Prevotella species. What this means, if anything, with respect to the long term health of individuals is not yet known. Short-term changes in one’s diet do alter the bacterial composition of one’s gut but apparently not in any stable way.
In the small intestine, where an overgrowth of normal gut bacteria would interfere with the absorption of nutrients, our intestinal cells secrete an antibacterial protein to keep the resident bacteria under control and at a distance. A similar antibacterial compound is found in insects which functions to keep the insect’s symbiotic bacteria from multiplying to the extent that they would harm or kill their host. Indeed, current research seems to indicate that most all higher organisms are partnered with a host of microbes, and often larger organisms as well, whose symbiotic functions are just beginning to be unraveled.
The word “biome” is used to describe a complex collection of plants, fungi, microorganisms, and larger organisms which live more or less compatibly in a specific habitat. Would it be too much of a stretch to refer to ourselves as biomes?
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