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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.
Some species of bacteria kill and then consume other microorganisms; these species are called predatory bacteria. [200] These include organisms such as Myxococcus xanthus , which forms swarms of cells that kill and digest any bacteria they encounter. [ 201 ]
Microbiology (from Ancient Greek μῑκρος (mīkros) 'small' βίος (bíos) 'life' and -λογία 'study of') is the scientific study of microorganisms, those being of unicellular (single-celled), multicellular (consisting of complex cells), or acellular (lacking cells).
The bacterial cell wall differs from that of all other organisms by the presence of peptidoglycan which is located immediately outside of the cell membrane. Peptidoglycan is made up of a polysaccharide backbone consisting of alternating N-Acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) residues in equal amounts.
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] [2] including the gastrointestinal tract, skin, mammary glands, seminal fluid, uterus, ovarian follicles, lung ...
The oral microbiota consists of all the microorganisms that exist in the mouth. It is the second largest of the human body and made of various bacteria, viruses, fungi and protozoa. [14] These organisms play an important role in oral and overall health. Anthony Van Leeuwenhoek was the first to view these organisms using a microscope he created ...
Spiral bacteria are another major bacterial cell morphology. [2] [30] [31] [32] Spiral bacteria can be sub-classified as spirilla, spirochetes, or vibrios based on the number of twists per cell, cell thickness, cell flexibility, and motility. [33] Bacteria are known to evolve specific traits to survive in their ideal environment. [34]
However, in the three-domain system, based upon molecular phylogenetics, prokaryotes are divided into two domains: Bacteria and Archaea. A third domain, Eukaryota, consists of organisms with nuclei. Prokaryotes evolved before eukaryotes, and lack nuclei, mitochondria, and most of the other distinct organelles that characterize the eukaryotic cell.