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42-578: See text Thauera is a genus of Gram-negative bacteria in the family Zoogloeaceae of the order Rhodocyclales of the Betaproteobacteria . The genus is named for the German microbiologist Rudolf Thauer . Most species of this genus are motile by flagella and are mostly rod-shaped. The species occur in wet soil and polluted freshwater. The genus includes the following species: Gram-negative Within this category, notable species include

84-459: A monophyletic clade and that no loss of the outer membrane from any species from this group has occurred. The proteobacteria are a major superphylum of gram-negative bacteria, including E. coli , Salmonella , Shigella , and other Enterobacteriaceae , Pseudomonas , Moraxella , Helicobacter , Stenotrophomonas , Bdellovibrio , acetic acid bacteria , Legionella etc. Other notable groups of gram-negative bacteria include

126-427: A monophyletic taxon (though not a clade ; his definition of monophyly requires a single common ancestor but does not require holophyly , the property that all descendants be encompassed by the taxon ) and refer to the group as a subkingdom "Negibacteria". Bacteria are traditionally classified based on their Gram-staining response into the gram-positive and gram-negative bacteria. Having just one membrane,

168-399: 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

210-657: A few conserved signature indel (CSI) in the HSP60 ( GroEL ) protein. In addition, a number of bacterial taxa (including Negativicutes , Fusobacteriota , Synergistota , and Elusimicrobiota ) that are either part of the phylum Bacillota (a monoderm group) or branches in its proximity are also found to possess a diderm cell structure. They lack the GroEL signature. The presence of this CSI in all sequenced species of conventional lipopolysaccharide-containing gram-negative bacterial phyla provides evidence that these phyla of bacteria form

252-621: 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

294-652: A multitude of species. Some of them cause primarily respiratory problems ( Klebsiella pneumoniae , Legionella pneumophila , Pseudomonas aeruginosa ), primarily urinary problems ( Escherichia coli , Proteus mirabilis , Enterobacter cloacae , Serratia marcescens ), and primarily gastrointestinal problems ( Helicobacter pylori , Salmonella enteritidis , Salmonella typhi ). Gram-negative bacteria associated with hospital-acquired infections include Acinetobacter baumannii , which cause bacteremia , secondary meningitis , and ventilator-associated pneumonia in hospital intensive-care units . Transformation

336-921: 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

378-435: A number of different observations, including that the gram-positive bacteria are the most sensitive to antibiotics and that the gram-negative bacteria are, in general, resistant to antibiotics, it has been proposed that the outer cell membrane in gram-negative bacteria (diderms) evolved as a protective mechanism against antibiotic selection pressure . Some bacteria such as Deinococcus , which stain gram-positive due to

420-793: 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

462-504: 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

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504-450: 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

546-519: A toxic reaction, resulting in fever, an increased respiratory rate, and low blood pressure . That is why some infections with gram-negative bacteria can lead to life-threatening septic shock . The outer membrane protects the bacteria from several antibiotics , dyes , and detergents that would normally damage either the inner membrane or the cell wall (made of peptidoglycan ). The outer membrane provides these bacteria with resistance to lysozyme and penicillin . The periplasmic space (space between

588-402: 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

630-428: 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

672-427: 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

714-426: 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 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

756-403: Is one of three processes for horizontal gene transfer , in which exogenous genetic material passes from one bacterium to another, the other two being conjugation (transfer of genetic material between two bacterial cells in direct contact) and transduction (injection of foreign DNA by a bacteriophage virus into the host bacterium). In transformation, the genetic material passes through

798-407: 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

840-421: 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 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

882-493: The CDC ), if any, governs the document being written. This is further explained at Gram staining § Orthographic note . Gram-positive In bacteriology , gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall . The Gram stain

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924-1020: The antimicrobial enzyme lysozyme produced by animals as part of their innate immune system . Furthermore, the outer leaflet of this membrane contains a complex lipopolysaccharide (LPS) whose lipid A component can trigger a toxic reaction when the bacteria are lysed by immune cells. This reaction may lead to septic shock , resulting in low blood pressure , respiratory failure , reduced oxygen delivery , and lactic acidosis . Several classes of antibiotics have been developed to target gram-negative bacteria, including aminopenicillins , ureidopenicillins , cephalosporins , beta-lactam - betalactamase inhibitor combinations (such as piperacillin-tazobactam ), folate antagonists , quinolones , and carbapenems . Many of these antibiotics also cover gram-positive bacteria. The antibiotics that specifically target gram-negative organisms include aminoglycosides , monobactams (such as aztreonam ), and ciprofloxacin . Conventional gram-negative (LPS-diderm) bacteria display

966-474: The cyanobacteria , spirochaetes , green sulfur , and green non-sulfur bacteria . Medically-relevant gram-negative diplococci include the four types that cause a sexually transmitted disease ( Neisseria gonorrhoeae ), a meningitis ( Neisseria meningitidis ), and respiratory symptoms ( Moraxella catarrhalis , A coccobacillus Haemophilus influenzae is another medically relevant coccal type. Medically relevant gram-negative bacilli include

1008-416: The model organism Escherichia coli , along with various pathogenic bacteria , such as Pseudomonas aeruginosa , Chlamydia trachomatis , and Yersinia pestis . They pose significant challenges in the medical field due to their outer membrane, which acts as a protective barrier against numerous antibiotics (including penicillin ), detergents that would normally damage the inner cell membrane, and

1050-418: 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

1092-501: 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,

1134-413: 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

1176-420: The diderm bacteria in which the outer cell membrane is made up of mycolic acid (e. g. Mycobacterium ). The conventional LPS- diderm group of gram-negative bacteria (e.g., Pseudomonadota , Aquificota , Chlamydiota , Bacteroidota , Chlorobiota , " Cyanobacteria ", Fibrobacterota , Verrucomicrobiota , Planctomycetota , Spirochaetota , Acidobacteriota ; " Hydrobacteria ") are uniquely identified by

1218-518: The following characteristics : 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 (0) and Mendocutes (var.). 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

1260-487: The gram-positive bacteria are also known as monoderm bacteria , while gram-negative bacteria, 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 bacteria. While this is often true, the classification system breaks down in some cases, with lineage groupings not matching

1302-461: 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

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1344-830: 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 has been studied in medically important gram-negative bacteria species such as Helicobacter pylori , Legionella pneumophila , Neisseria meningitidis , Neisseria gonorrhoeae , Haemophilus influenzae and Vibrio cholerae . It has also been studied in gram-negative species found in soil such as Pseudomonas stutzeri , Acinetobacter baylyi , and gram-negative plant pathogens such as Ralstonia solanacearum and Xylella fastidiosa . One of

1386-465: 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

1428-606: 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

1470-401: 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

1512-526: 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,

1554-437: 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 ,

1596-509: The peri-plasmic space. Other classes of drugs that have gram negative spectrum include cephalosporins , monobactams ( aztreonam ), aminoglycosides, quinolones , macrolides , chloramphenicol , folate antagonists , and carbapenems . The adjectives gram-positive and gram-negative derive from the surname of Hans Christian Gram , a Danish bacteriologist; as eponymous adjectives , their initial letter can be either capital G or lower-case g , depending on which style guide (e.g., that of

1638-419: The presence of a thick peptidoglycan layer, but 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 (LPS); the archetypical diderm bacteria, in which the outer cell membrane contains lipopolysaccharide; and

1680-459: The several unique characteristics of gram-negative bacteria is the structure of the bacterial outer membrane . The outer leaflet of this membrane contains lipopolysaccharide (LPS), whose lipid A portion acts as an endotoxin . If gram-negative bacteria enter the circulatory system , LPS can trigger an innate immune response , activating the immune system and producing cytokines (hormonal regulators). This leads to inflammation and can cause

1722-426: The staining result. Thus, Gram staining cannot be reliably used to assess familial relationships of bacteria. Nevertheless, staining often gives reliable information about the composition of the cell membrane, distinguishing between the presence or absence of an outer lipid membrane . Of these two structurally distinct groups of prokaryotic organisms, monoderm prokaryotes are thought to be ancestral. Based upon

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1764-403: The two cell membranes) also contains enzymes which break down or modify antibiotics. Drugs commonly used to treat gram negative infections include amino, carboxy and ureido penicillins ( ampicillin , amoxicillin , pipercillin , ticarcillin ). These drugs may be combined with beta-lactamase inhibitors to combat the presence of enzymes that can digest these drugs (known as beta-lactamases ) in

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