Bacteria (/ b æ k ˈ t ɪər i ə / ; common noun bacteria, singular bacterium) are a type of biological cell. They constitute a large domain of prokaryotic microorganisms . Typically a few micrometres in length, bacteria have a number of shapes , ranging from spheres to rods and spirals .
Bacteria vary widely in size and shape, but in general they are at least ten times larger than viruses. A typical bacterium is about 1 µm (one micrometer) in diameter, so a thousand bacteria lined up would be one millimeter long. There are about five nonillion (5×10 30) bacteria on Earth. Bacteria are identified and grouped by their shapes.
Gram-positive bacteria are capable of causing serious and sometimes fatal infections in newborn infants. Novel species of clinically relevant gram-positive bacteria also include Catabacter hongkongensis, which is an emerging pathogen belonging to Firmicutes. Bacterial transformation
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Pathogenic bacteria are bacteria that can cause disease. This article deals with human pathogenic bacteria. Although most bacteria are harmless or often beneficial, some are pathogenic, with the number of species estimated as fewer than a hundred that are seen to cause infectious diseases in humans.SpeciesSpeciesTransmissionDiseasesActinomycosis: painful abscesses in the mouth, lungs, or gastrointestinal tract.Contact with cattle, sheep, goats and horses Spores enter through inhalation or through abrasionsAnthrax: pulmonary, gastrointestinal and/or cutaneous symptoms.Abscesses in gastrointestinal tract, pelvic cavity and lungsContact with respiratory droplets expelled by infected human hosts.Whooping cough Secondary bacterial pneumonia
- Bacterial transformation
- Medical treatment
Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the gram-staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane. Gram-negative bacteria are found everywhere, in virtually all environments on Earth that support life. The gram-negative bacteria include the model organism Escherichia c
Gram-negative bacteria display these characteristics: 1. An inner cell membrane is present 2. A thin peptidoglycan layer is present 3. Has outer membrane containing lipopolysaccharides in its outer leaflet and phospholipids in the inner leaflet 4. Porins exist in the outer membrane, which act like pores for particular molecules 5. Between the outer membrane and the cytoplasmic membrane there is a space filled with a concentrated gel-like substance called periplasm 6. The S-layer is directly atta
Along with cell shape, Gram staining is a rapid diagnostic tool and once was used to group species at the subdivision of Bacteria. Historically, the kingdom Monera was divided into four divisions based on Gram staining: Firmacutes, Gracillicutes, Mollicutes and Mendocutes. Since 1987, the monophyly of the gram-negative bacteria has been disproven with molecular studies. However some authors, such as Cavalier-Smith still treat them as a monophyletic taxon and refer to the group as a subkingdom "N
Bacteria are traditionally classified based on their Gram-staining response into the gram-positive and gram-negative bacteria. Having just one membrane the gram-positive bacteria are also known as monoderm bacteria, and gram-negative having two membranes are also known as diderm bacteria. It was traditionally thought that the groups represent lineages, i.e. the extra membrane only evolved once, such that gram-negative bacteria are more closely related to one another than to any gram-positive bac
Transformation is one of three processes for horizontal gene transfer, in which exogenous genetic material passes from bacterium to another, the other two being conjugation and transduction. In transformation, the genetic material passes through the intervening medium, and uptake is completely dependent on the recipient bacterium. As of 2014 about 80 species of bacteria were known to be capable of transformation, about evenly divided between gram-positive and gram-negative bacteria; the number m
One of the several unique characteristics of gram-negative bacteria is the structure of the bacterial outer membrane. The outer leaflet of this membrane comprises a complex lipopolysaccharide whose lipid portion acts as an endotoxin. If gram-negative bacteria enter the circulatory system, the LPS can cause a toxic reaction. This results in fever, an increased respiratory rate, and low blood pressure. This may lead to life-threatening septic shock. The outer membrane protects the bacteria from se
In comparison to batch culture, bacteria are maintained in exponential growth phase, and the growth rate of the bacteria is known. Related devices include turbidostats and auxostats . When Escherichia coli is growing very slowly with a doubling time of 16 hours in a chemostat most cells have a single chromosome.
Helicobacter pylori, previously known as Campylobacter pylori, is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is thought to have evolved in order to penetrate the mucoid lining of the stomach and thereby establish infection.
Cyanobacteria / s aɪ ˌ æ n oʊ b æ k ˈ t ɪər i ə /, also known as Cyanophyta, are a phylum of prokaryotes consisting of both free-living photosynthetic bacteria and the endosymbiotic plastids that are present in the Archaeplastida, the autotrophic eukaryotes that include the red and green algae and land plants.
Bacteriile sunt microorganisme procariote și alcătuiesc domeniul Bacteria (sinonim Eubacteria). Prezintă de cele mai multe ori o lungime de câțiva micrometri , dar sunt foarte diverse din punct de vedere morfologic, regăsindu-se sub formă sferică , alungită sau spiralată (elicoidală).