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In bacteria, gene transfer occurs by three processes. These are virus-mediated transduction; [14] conjugation; [16] and natural transformation. [17] Transduction of bacterial genes by bacteriophage viruses appears to reflect occasional errors during intracellular assembly of virus particles, rather than an adaptation of the host bacteria. There ...
This figure depicts fimbriae adhesion. In this process the fimbriae of a bacterial cell (right) adhere to specific proteins, called receptors, found on the outer membrane of a host cell (left). They do this by a specific interaction between the receptors of the host cell and the perfectly matched adhesions found on the bacteria's fimbriae.
Many structural features are unique to bacteria and are not found among archaea or eukaryotes. Because of the simplicity of bacteria relative to larger organisms and the ease with which they can be manipulated experimentally, the cell structure of bacteria has been well studied, revealing many biochemical principles that have been subsequently ...
Structure of a typical prokaryotic cell. Prokaryotes include bacteria and archaea, two of the three domains of life. Prokaryotic cells were the first form of life on Earth, characterized by having vital biological processes including cell signaling. They are simpler and smaller than eukaryotic cells, and lack a nucleus, and other membrane-bound ...
[200] [201] Referred to as "normal flora", [202] or "commensals", [203] these bacteria usually cause no harm but may occasionally invade other sites of the body and cause infection. Escherichia coli is a commensal in the human gut but can cause urinary tract infections. [ 204 ]
Koch found that he could transmit anthrax from one animal to another by taking a small sample of blood from the infected animal and injecting it into a healthy one, and this caused the healthy animal to become sick. He also found that he could grow the bacteria in a nutrient broth, then inject it into a healthy animal, and cause illness.
The viral eukaryogenesis hypothesis posits that eukaryotes are composed of three ancestral elements: a viral component that became the modern nucleus; a prokaryotic cell (an archaeon according to the eocyte hypothesis) which donated the cytoplasm and cell membrane of modern cells; and another prokaryotic cell (here bacterium) that, by endocytosis, became the modern mitochondrion or chloroplast.
The next major change in cell structure came when bacteria were engulfed by eukaryotic cells, in a cooperative association called endosymbiosis. [ 20 ] [ 21 ] The engulfed bacteria and the host cell then underwent coevolution, with the bacteria evolving into either mitochondria or hydrogenosomes . [ 22 ]