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34-473: The Actinomycetota (or Actinobacteria ) are a diverse phylum of Gram-positive bacteria with high GC content . They can be terrestrial or aquatic . They are of great importance to land flora because of their contributions to soil systems. In soil they help to decompose the organic matter of dead organisms so the molecules can be taken up anew by plants . While this role is also played by fungi , Actinomycetota are much smaller and likely do not occupy

68-399: A cytoplasmic membrane and an outer cell membrane; they contain only a thin layer of peptidoglycan (2–3 nm) between these membranes. The presence of inner and outer cell membranes defines a new compartment in these cells: the periplasmic space or the periplasmic compartment. These bacteria have been designated as diderm bacteria . The distinction between the monoderm and diderm bacteria

102-675: A diverse set of ecological niches. Gordonibacter species are the only members capable of motility by means of flagella within the class. Several species within the Coriobacteriia class have been implicated with human diseases that range in severity. Atopobium , Olsenella , and Cryptobacterium species have responsible for human oral infections including periodontitis , halitosis , and other endodontic infections. Eggerthella species have been associated with severe blood bacteraemia and ulcerative colitis . Historically, all Coriobacteriia species were placed within

136-650: A low G+C content. Analysis of glutamine synthetase sequence has been suggested for phylogenetic analysis of the Actinomycetota. Rubrobacteria Thermoleophilia Coriobacteriia Acidimicrobiia Nitriliruptoria Actinomycetia Chloroflexota Rubrobacteria Thermoleophilia Coriobacteriia Acidimicrobiia Nitriliruptoria Actinomycetia "Humimicrobiia" "Aquicultoria" Coriobacteriia "Geothermincolia" Rubrobacteria Thermoleophilia Acidimicrobiia Nitriliruptoridae Actinobacteridae The currently accepted taxonomy

170-621: A monophyletic clade and that no loss of the outer membrane from any species from this group has occurred. In the classical sense, six gram-positive genera are typically pathogenic in humans. Two of these, Streptococcus and Staphylococcus , are cocci (sphere-shaped). The remaining organisms are bacilli (rod-shaped) and can be subdivided based on their ability to form spores . The non-spore formers are Corynebacterium and Listeria (a coccobacillus), whereas Bacillus and Clostridium produce spores. The spore-forming bacteria can again be divided based on their respiration : Bacillus

204-972: A number of bacterial taxa (viz. Negativicutes , Fusobacteriota , Synergistota , and Elusimicrobiota ) that are either part of the phylum Bacillota or branch in its proximity are found to possess a diderm cell structure. However, a conserved signature indel (CSI) in the HSP60 ( GroEL ) protein distinguishes all traditional phyla of gram-negative bacteria (e.g., Pseudomonadota , Aquificota , Chlamydiota , Bacteroidota , Chlorobiota , " Cyanobacteria ", Fibrobacterota , Verrucomicrobiota , Planctomycetota , Spirochaetota , Acidobacteriota , etc.) from these other atypical diderm bacteria, as well as other phyla of monoderm bacteria (e.g., Actinomycetota , Bacillota , Thermotogota , Chloroflexota , etc.). The presence of this CSI in all sequenced species of conventional LPS ( lipopolysaccharide )-containing gram-negative bacterial phyla provides evidence that these phyla of bacteria form

238-793: A recipient host bacterium). 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 might be an overestimate since several of the reports are supported by single papers. Transformation among gram-positive bacteria has been studied in medically important species such as Streptococcus pneumoniae , Streptococcus mutans , Staphylococcus aureus and Streptococcus sanguinis and in gram-positive soil bacteria Bacillus subtilis and Bacillus cereus . The adjectives gram-positive and gram-negative derive from

272-508: A single membrane, but stain gram-negative due to either lack of the peptidoglycan layer, as in the mycoplasmas , or their inability to retain the Gram stain because of their cell wall composition—also show close relationship to the gram-positive bacteria. For the bacterial cells bounded by a single cell membrane, the term monoderm bacteria has been proposed. In contrast to gram-positive bacteria, all typical gram-negative bacteria are bounded by

306-459: A single order ( Coriobacteriales ) and a single family ( Coriobacteriaceae ). This view, however, was not reflective of accurate evolutionary interrelationships within the class. The current taxonomic view is justified by the presence of several conserved signature indels (CSIs) that have been found at the different taxonomic ranks. These CSIs are specific and represent synapomorphic characteristics that can be used to distinguish groups within

340-455: A surface layer called an S-layer . In gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Gram-negative bacteria's S-layer is attached directly to the outer membrane . Specific to gram-positive bacteria is the presence of teichoic acids in the cell wall. Some of these are lipoteichoic acids, which have a lipid component in the cell membrane that can assist in anchoring

374-432: A thin layer of peptidoglycan. Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through an optical microscope . This is because the thick layer of peptidoglycan in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test. Conversely, gram-negative bacteria cannot retain

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408-402: Is a facultative anaerobe , while Clostridium is an obligate anaerobe . Also, Rathybacter , Leifsonia , and Clavibacter are three gram-positive genera that cause plant disease. 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

442-428: Is ambiguous as it refers to three distinct aspects (staining result, envelope organization, taxonomic group), which do not necessarily coalesce for some bacterial species. The gram-positive and gram-negative staining response is also not a reliable characteristic as these two kinds of bacteria do not form phylogenetic coherent groups. However, although Gram staining response is an empirical criterion, its basis lies in

476-427: Is an emerging pathogen belonging to Bacillota . Transformation is one of three processes for horizontal gene transfer , in which exogenous genetic material passes from a donor bacterium to a recipient bacterium, the other two processes being conjugation (transfer of genetic material between two bacterial cells in direct contact) and transduction (injection of donor bacterial DNA by a bacteriophage virus into

510-528: Is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). Gram-positive bacteria The Gram stain is used by microbiologists to place bacteria into two main categories, Gram-positive (+) and Gram-negative (-). Gram-positive bacteria have a thick layer of peptidoglycan within the cell wall, and Gram-negative bacteria have

544-407: Is supported by conserved signature indels in a number of important proteins (viz. DnaK, GroEL). Of these two structurally distinct groups of bacteria, monoderms are indicated to be ancestral. Based upon a number of observations including that the gram-positive bacteria are the major producers of antibiotics and that, in general, gram-negative bacteria are resistant to them, it has been proposed that

578-575: The Coriobacteriia , both at the family and order levels. The distinction of the orders within the Coriobacteriia is also supported phylogenetic tree branching and by consistent characteristics; members belonging to the Coriobacteriales are glucose-fermenting, saccharolytic species while the Eggerthellales order has species that are consistently unable to ferment glucose and are asaccharolytic. CSIs have also been used to resolve

612-418: The absence of the outer membrane. In general, the following characteristics are present in gram-positive bacteria: Only some species have a capsule , usually consisting of polysaccharides . Also, only some species are flagellates , and when they do have flagella , have only two basal body rings to support them, whereas gram-negative have four. Both gram-positive and gram-negative bacteria commonly have

646-501: The archetypical diderm bacteria where the outer cell membrane contains lipopolysaccharide, and the diderm bacteria where outer cell membrane is made up of mycolic acid . In general, gram-positive bacteria are monoderms and have a single lipid bilayer whereas gram-negative bacteria are diderms and have two bilayers. Exceptions include: Some Bacillota species are not gram-positive. The class Negativicutes, which includes Selenomonas , are diderm and stain gram-negative. Additionally,

680-468: The gram-positive bacteria was challenged, with major implications for the therapeutic and general study of these organisms. Based on molecular studies of the 16S sequences, Woese recognised twelve bacterial phyla . Two of these were gram-positive and were divided on the proportion of the guanine and cytosine content in their DNA . The high G + C phylum was made up of the Actinobacteria , and

714-580: The intestine. Although some of the largest and most complex bacterial cells belong to the Actinomycetota, the group of marine Actinomarinales has been described as possessing the smallest free-living prokaryotic cells. Some Siberian or Antarctic Actinomycetota are said to be the oldest living organism on Earth, frozen in permafrost at around half a million years ago. The symptoms of life were detected by CO 2 release from permafrost samples 640 kya or younger. Most Actinomycetota of medical or economic significance are in class Actinomycetia , and belong to

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748-471: The kingdom Monera was divided into four divisions based primarily on Gram staining: Bacillota (positive in staining), Gracilicutes (negative in staining), Mollicutes (neutral in staining) and Mendocutes (variable in staining). Based on 16S ribosomal RNA phylogenetic studies of the late microbiologist Carl Woese and collaborators and colleagues at the University of Illinois , the monophyly of

782-448: The largest of bacterial genera, Streptomyces . Streptomyces and other actinomycetota are major contributors to biological buffering of soils. They are also the source of many antibiotics . The Actinomycetota genus Bifidobacterium is the most common bacteria in the microbiome of human infants. Although adults have fewer bifidobacteria, intestinal bifidobacteria help maintain the mucosal barrier and reduce lipopolysaccharide in

816-562: The low G + C phylum contained the Firmicutes . The Actinomycetota include the Corynebacterium , Mycobacterium , Nocardia and Streptomyces genera. The (low G + C) Bacillota, have a 45–60% GC content, but this is lower than that of the Actinomycetota. Although bacteria are traditionally divided into two main groups, gram-positive and gram-negative, based on their Gram stain retention property, this classification system

850-401: The marked differences in the ultrastructure and chemical composition of the bacterial cell wall, marked by the absence or presence of an outer lipid membrane. All gram-positive bacteria are bounded by a single-unit lipid membrane, and, in general, they contain a thick layer (20–80 nm) of peptidoglycan responsible for retaining the Gram stain. A number of other bacteria—that are bounded by

884-492: The order Actinomycetales . While many of these cause disease in humans, Streptomyces is notable as a source of antibiotics . Of those Actinomycetota not in the Actinomycetales, Gardnerella is one of the most researched. Classification of Gardnerella is controversial, and MeSH catalogues it as both a Gram-positive and Gram-negative organism. Actinomycetota, especially Streptomyces spp., are recognized as

918-526: The outer cell membrane in gram-negative bacteria (diderms) has evolved as a protective mechanism against antibiotic selection pressure. Some bacteria, such as Deinococcus , which stain gram-positive due to the presence of a thick peptidoglycan layer and also possess an outer cell membrane are suggested as intermediates in the transition between monoderm (gram-positive) and diderm (gram-negative) bacteria. The diderm bacteria can also be further differentiated between simple diderms lacking lipopolysaccharide,

952-437: The peptidoglycan. Along with cell shape , Gram staining is a rapid method used to differentiate bacterial species. Such staining, together with growth requirement and antibiotic susceptibility testing, and other macroscopic and physiologic tests, forms a basis for practical classification and subdivision of the bacteria (e.g., see figure and pre-1990 versions of Bergey's Manual of Systematic Bacteriology ). Historically ,

986-431: The phylogenetic position of the Coriobacteriia among all bacteria where they have been found exclusively for all species within the class, delineating them from other Actinomycetota . The Coriobacteriia are an early branching lineage within the Actinomycetota phylum The deep branching of the class has led to dispute over its membership within the phylum and whether or not it is a true Actinomycetota group. A CSI in

1020-403: The plant's saccharides . Other species, such as many members of the genus Mycobacterium , are important pathogens . Beyond the great interest in Actinomycetota for their soil role, much is yet to be learned about them. Although currently understood primarily as soil bacteria, they might be more abundant in fresh waters. Actinomycetota is one of the dominant bacterial phyla and contains one of

1054-636: The producers of many bioactive metabolites that are useful to humans in medicine, such as antibacterials, antifungals, antivirals, antithrombotics, immunomodifiers, antitumor drugs, and enzyme inhibitors; and in agriculture, including insecticides, herbicides, fungicides, and growth-promoting substances for plants and animals. Actinomycetota-derived antibiotics that are important in medicine include aminoglycosides, anthracyclines, chloramphenicol, macrolide, tetracyclines, etc. Actinomycetota have high guanine and cytosine content in their DNA . The G+C content of Actinomycetota can be as high as 70%, though some may have

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1088-424: The same ecological niche . In this role the colonies often grow extensive mycelia , as fungi do, and the name of an important order of the phylum, Actinomycetales (the actinomycetes), reflects that they were long believed to be fungi. Some soil actinomycetota (such as Frankia ) live symbiotically with the plants whose roots pervade the soil, fixing nitrogen for the plants in exchange for access to some of

1122-590: The surname of Hans Christian Gram ; as eponymous adjectives , their initial letter can be either capital G or lower-case g , depending on which style guide (e.g., that of the CDC ), if any, governs the document being written. Coriobacteriia The Coriobacteriia are a class of Gram-positive bacteria within the Actinomycetota phylum. Species within this group are non sporulating , strict or facultative anaerobes that are capable of thriving in

1156-602: The violet stain after the decolorization step; alcohol used in this stage degrades the outer membrane of gram-negative cells, making the cell wall more porous and incapable of retaining the crystal violet stain. Their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane , causing them to take up the counterstain ( safranin or fuchsine ) and appear red or pink. Despite their thicker peptidoglycan layer, gram-positive bacteria are more receptive to certain cell wall –targeting antibiotics than gram-negative bacteria, due to

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