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e. A microorganism, or microbe, [ a ] is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from sixth century BC India.
The germ theory of disease is the currently accepted scientific theory for many diseases. It states that microorganisms known as pathogens or "germs" can cause disease. These small organisms, which are too small to be seen without magnification, invade humans, other animals, and other living hosts. Their growth and reproduction within their ...
Bacteria (/ b æ k ˈ t ɪər i ə / ⓘ; sg.: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats.
The Earth was formed at 4.54 Gya, and the earliest evidence of life on Earth dates from at least 3.8 Gya from Western Australia. Some studies have suggested that fossil micro-organisms may have lived within hydrothermal vent precipitates dated 3.77 to 4.28 Gya from Quebec , soon after ocean formation 4.4 Gya during the Hadean .
The evolution of bacteria has progressed over billions of years since the Precambrian time with their first major divergence from the archaeal / eukaryotic lineage roughly 3.2-3.5 billion years ago. [1][2] This was discovered through gene sequencing of bacterial nucleoids to reconstruct their phylogeny. Furthermore, evidence of permineralized ...
Flora (microbiology) In microbiology, collective bacteria and other microorganisms in a host are historically known as flora. Although microflora is commonly used, the term microbiota is becoming more common as microflora is a misnomer. Flora pertains to the Kingdom Plantae. Microbiota includes Archaea, Bacteria, Fungi and Protists.
The term pathogen came into use in the 1880s. [ 2 ][ 3 ] Typically, the term pathogen is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus. [ 4 ][ 5 ][ 6 ] Small animals, such as helminths and insects, can also cause or transmit disease. However, these animals are usually ...
Graphic depicting the human skin microbiota, with relative prevalences of various classes of bacteria. The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding anatomical sites in which they reside, [1] including the gastrointestinal tract, skin, mammary glands, seminal fluid, uterus, ovarian follicles, lung ...