We share the planet and our own bodies with an unseen multitude of microscopic organisms.

Plants and animals are in many respects huge ecosystems of diverse microscopic organisms, rather than individuals of one species. This microbiota includes yeast, fungi, bacteria, viruses and protists. In humans the microbiota may compose 1 kg to 2.25 kg of a person’s body weight. The number of human cells in a person’s body are greatly outnumbered (over 10 times) by the alien cells of microbiotic organisms which form vast resident colonies on the surface of internal and external tissue. It is also estimated that between 100 and 200 human genes are actually under the control of resident bacteria.

Bacteria are the most numerous living organisms on Earth. They are independent single celled organisms with no true nucleus; their DNA is coiled in a nucleoid. They reproduce by splitting in a process called binary fission, which allows them to multiply rapidly and to change by genetic mutation. There is an enormous diversity of bacteria species, in one study 30 grams of forest soil was found to contain over ½ million species of bacteria.

Bacteria and their hosts live together in a symbiotic relationship. The symbiotic association may be of three types. Commensal, where there is no obvious harm or help to either party. Mutualistic, where a benefit occurs to both parties. Beneficial bacteria help their host by aiding processes such as digestion or by creating conditions unfavourable to other harmful organisms. Parasitic, where no benefit is conferred on the host. Parasitic bacteria can become pathogenic if they harm the host by destroying cells or producing damaging toxins. Pathogenic bacteria may be invaders or opportunistic “native” species which react to a change in conditions, such as a compromised host immune system. Diseases such as tetanus, bubonic plague, typhoid, cholera and TB are caused by bacterial pathogens.

Bacteria play a key role in the cycle of chemical exchange on Earth, they decompose waste and dead organisms into nutrients, produce oxygen, fix nitrogen into a useable form and are essential for plants and animals to obtain and process nutrients. Without bacteria, life as we know it would rapidly disappear.

Our society regards bacteria as the enemy, however as more is discovered about the diversity of bacteria, their symbiotic relationship with other living things and their role in the global ecosystem, it is becoming clear that the purely “anti bacterial” approach is simplistic. While it is beyond doubt that improved sanitation, hygiene and antibiotics have improved human health, the removal of vast numbers of bacterial species through wide use of antibiotics in medicine and food production and the everyday use of antibacterial products are affecting systems we do not yet understand. Changes to human microbiota may be implicated in the increase in allergies and asthma and may also affect auto immune and metabolic diseases and mental illness.


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