Gram-positive
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bacteriology Bacteriology is the branch and specialty of biology that studies the Morphology (biology), morphology, ecology, genetics and biochemistry of bacteria as well as many other aspects related to them. This subdivision of microbiology involves the identi ...
, gram-positive bacteria are
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometre The micrometre (Amer ...
that give a positive result in the
Gram stain In microbiology and bacteriology, Gram stain (Gram staining or Gram's method), is a method of staining used to classify bacterial species into two large groups: gram-positive bacteria and gram-negative bacteria. The name comes from the Danish bac ...
test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biolog ...
. Gram-positive bacteria take up the
crystal violet Crystal violet or gentian violet, also known as methyl violet 10B or hexamethyl pararosaniline chloride, is a triphenylmethane, triarylmethane dye used as a histological stain and in Gram staining, Gram's method of classifying bacteria. Crystal ...
stain used in the test, and then appear to be purple-coloured when seen through an
optical microscope The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible spectrum, visible light and a system of lens (optics), lenses to generate magnified images of small objects. Optical microscopes ...
. This is because the thick
peptidoglycan Peptidoglycan or murein is a unique large macromolecule, a polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units ...
layer in the bacterial cell wall retains the
stain A stain is a discoloration that can be clearly distinguished from the surface, material, or medium it is found upon. They are caused by the chemical or physical interaction of two dissimilar materials. Accidental staining may make materials ap ...
after it is washed away from the rest of the sample, in the decolorization stage of the test. Conversely,
gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the Crystal violet, 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 peptidogly ...
cannot retain the violet stain after the decolorization step;
alcohol Alcohol most commonly refers to: * Alcohol (chemistry) In chemistry, an alcohol is a type of organic compound that carries at least one hydroxyl () functional group bound to a Saturated and unsaturated compounds, saturated carbon atom. The ...
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 The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the cytoplasm, interior of all Cell (biology), cells from th ...
and a
bacterial outer membrane The bacterial outer membrane is found in gram-negative bacteria. Its composition is distinct from that of the inner cell membrane, cytoplasmic cell membrane - among other things, the outer leaflet of the outer membrane of many gram-negative bact ...
, causing them to take up the
counterstain A counterstain is a stain A stain is a discoloration that can be clearly distinguished from the surface, material, or medium it is found upon. They are caused by the chemical or physical interaction of two dissimilar materials. Accidental sta ...
(
safranin Safranin (Safranin O or basic red 2) is a biological stain used in histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissue (biology), tissues ...
or
fuchsine Fuchsine (sometimes spelled fuchsin) or rosaniline hydrochloride is a magenta Magenta () is a color that is variously defined as pinkish- purplish- red, reddish-purplish-pink or mauvish- crimson. On color wheels of the RGB (additive) and ...
) and appear red or pink. Despite their thicker peptidoglycan layer, gram-positive bacteria are more receptive to certain
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biolog ...
targeting
antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
than gram-negative bacteria, due to the absence of the outer membrane.


Characteristics

In general, the following characteristics are present in gram-positive bacteria: # Cytoplasmic lipid membrane # Thick
peptidoglycan Peptidoglycan or murein is a unique large macromolecule, a polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units ...
layer #
Teichoic acids Teichoic acids (''cf.'' Classical Greek language, Greek τεῖχος, ''teīkhos'', "wall", to be specific a fortification wall, as opposed to τοῖχος, ''toīkhos'', a regular wall) are bacterial copolymers of glycerol phosphate or ribito ...
and lipoids are present, forming
lipoteichoic acid Lipoteichoic acid (LTA) is a major constituent of the cell wall of gram-positive bacteria. These organisms have an inner (or cytoplasmic) membrane and, external to it, a thick (up to 80 nanometer) peptidoglycan layer. The structure of LTA varies be ...
s, which serve as
chelating Chelation is a type of bonding of ions An ion () is an atom or molecule with a net electric charge, electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge ...
agents, and also for certain types of adherence. # Peptidoglycan chains are cross-linked to form rigid cell walls by a bacterial enzyme
DD-transpeptidase DD-transpeptidase (, ''DD-peptidase'', ''DD-transpeptidase'', ''DD-carboxypeptidase'', ''D-alanyl-D-alanine carboxypeptidase'', ''D-alanyl-D-alanine-cleaving-peptidase'', ''D-alanine carboxypeptidase'', ''D-alanyl carboxypeptidase'', and ''serine- ...
. # A much smaller volume of
periplasm The periplasm is a concentrated gel-like matrix (biology), matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane called the ''periplasmic space'' in gram-negative bacterium, bacteria. Using cryo-electron micro ...
than that in gram-negative bacteria. Only some species have a capsule, usually consisting of
polysaccharides Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic bond, glycosidic linkages. This carbohydrate c ...
. Also, only some species are
flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagellum, flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes ...
s, and when they do have
flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide Motility#Cellular level, motility. Many protists with flagella are termed as flagellates. A m ...
, have only two
basal body A basal body (synonymous with basal granule, kinetosome, and in older cytological literature with blepharoplast) is a protein structure found at the base of a eukaryotic undulipodium (cilium or flagellum). The basal body was named by Theodor Wi ...
rings to support them, whereas gram-negative have four. Both gram-positive and gram-negative bacteria commonly have a surface layer called an
S-layer An S-layer (surface layer) is a part of the cell envelope found in almost all archaea, as well as in many types of bacteria. The S-layers of both archaea and bacteria consists of a monomolecular layer composed of only one (or, in a few cases, two) i ...
. 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 acid Teichoic acids (''cf.'' Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, ...
s in the cell wall. Some of these are lipoteichoic acids, which have a lipid component in the cell membrane that can assist in anchoring the peptidoglycan.


Classification

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 the full basis for classification and subdivision of the bacteria (e.g., see figure and pre-1990 versions of ''
Bergey's Manual of Systematic Bacteriology ''Bergey's Manual of Systematic Bacteriology'' is the main resource for determining the identity of prokaryotic organisms, emphasizing bacterial species, using every characterizing aspect. The manual was published subsequent to the ''Bergey's Manu ...
'').
Historically History (derived ) is the systematic study and the documentation of the human activity. The time period of event before the History of writing#Inventions of writing, invention of writing systems is considered prehistory. "History" is an umbr ...
, the kingdom
Monera Monera (/məˈnɪərə/) (Greek - μονήρης (monḗrēs), "single", "solitary") is a Kingdom (biology), biological kingdom that is made up of prokaryotes. As such, it is composed of single-celled organisms that lack a Cell nucleus, nucleu ...
was divided into four divisions based primarily on Gram staining:
Bacillota The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have gram-positive bacteria, gram-positive cell wall structure. The renaming of phyla such as Firmicutes in 2021 remains controversial among microbiologists, many of whom ...
(positive in staining),
Gracilicutes Gracilicutes (Latin: ''gracilis'', slender, and ''cutis'', skin, referring to the cell wall) is a clade in bacterial phylogeny. Traditionally gram staining results were most commonly used as a classification tool, consequently until the advent of ...
(negative in staining),
Mollicutes Mollicutes is a class of bacteria distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin ''mollis'' (meaning "soft" or "pliable"), and ''cutis'' (meaning "skin"). Individuals are very small, typically only 0. ...
(neutral in staining) and Mendocutes (variable in staining). Based on
16S ribosomal RNA 16svedberg, S ribosomal RNA (or 16Svedberg, S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome (SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The genes coding for it are referr ...
phylogenetic studies of the late microbiologist
Carl Woese Carl Richard Woese (; July 15, 1928 – December 30, 2012) was an American microbiologist and biophysicist. Woese is famous for defining the Archaea (a new domain (biology), domain of life) in 1977 through a pioneering phylogenetic taxonomy (biol ...
and collaborators and colleagues at the
University of Illinois The University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public university, public land-grant university, land-grant research university in Illinois in the twin cities of Champaign, Illinois, Champai ...
, the
monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...
of 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 Bacterial phylum, phyla constitute the major lineages of the domain ''Bacteria''. While the exact definition of a bacterial phylum is debated, a popular definition is that a bacterial phylum is a Monophyly, monophyletic lineage of bacteria whos ...
. Two of these were gram-positive and were divided on the proportion of the
guanine Guanine () (symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between othe ...
and
cytosine Cytosine () (nucleoside#List of nucleosides and corresponding nucleobases, symbol C or Cyt) is one of the four Nucleobase, nucleobases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, ...
content in their DNA. The high G + C phylum was made up of the Actinobacteria and the low G + C phylum contained the
Firmicutes The Bacillota (synonym Firmicutes) are a phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term divis ...
. The Actinomycetota include the ''
Corynebacterium ''Corynebacterium'' () is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of ...
'', ''
Mycobacterium ''Mycobacterium'' is a genus of over 190 species in the phylum Actinomycetota, assigned its own family, Mycobacteriaceae. This genus includes pathogens known to cause serious diseases in mammals, including tuberculosis (''Mycobacterium tuberculos ...
'', ''
Nocardia ''Nocardia'' is a genus of weakly staining Gram-positive, catalase, catalase-positive, rod-shaped bacteria. It forms partially acid-fast beaded branching filaments (acting as fungi, but being truly bacteria). It contains a total of 85 species. ...
'' and ''
Streptomyces ''Streptomyces'' is the largest genus of Actinomycetota and the type genus of the family Streptomycetaceae. Over 500 species of ''Streptomyces'' bacteria have been described. As with the other Actinomycetota, streptomycetes are gram-positi ...
'' genera. The (low G + C) Bacillota, have a 45–60% GC content, but this is lower than that of the Actinomycetota.


Importance of the outer cell membrane in bacterial classification

Although bacteria are traditionally divided into two main groups, gram-positive and gram-negative, based on their Gram stain retention property, this classification system 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 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 a single membrane, but stain gram-negative due to either lack of the peptidoglycan layer, as in the
mycoplasma ''Mycoplasma'' is a genus of bacteria that, like the other members of the class ''Mollicutes'', lack a cell wall around their cell membranes. Peptidoglycan (murein) is absent. This characteristic makes them naturally resistant to antibiotics ...
s, 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 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 The periplasm is a concentrated gel-like matrix (biology), matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane called the ''periplasmic space'' in gram-negative bacterium, bacteria. Using cryo-electron micro ...
or the periplasmic compartment. These bacteria have been designated as
diderm bacteria Gram-negative bacteria are bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few ...
. The distinction between the monoderm and diderm bacteria 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 the outer cell membrane in gram-negative bacteria (diderms) has evolved as a protective mechanism against
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
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, 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 Mycolic acids are long fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most natura ...
.


Exceptions

In general, gram-positive bacteria are monoderms and have a single
lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cell (biology), cells. The cell membranes of almost all organis ...
whereas gram-negative bacteria are diderms and have two bilayers. Some taxa lack peptidoglycan (such as the class
Mollicutes Mollicutes is a class of bacteria distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin ''mollis'' (meaning "soft" or "pliable"), and ''cutis'' (meaning "skin"). Individuals are very small, typically only 0. ...
, some members of the
Rickettsiales The Rickettsiales, informally called rickettsias, are an order of small Alphaproteobacteria Alphaproteobacteria is a Class (biology), class of bacteria in the phylum Pseudomonadota (formerly Proteobacteria). The Magnetococcales and Mariprofund ...
, and the insect-endosymbionts of the Enterobacteriales) and are gram-variable. This, however, does not always hold true. The
Deinococcota ''Deinococcota'' (synonym, ''Deinococcus-Thermus'') is a phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botan ...
have gram-positive stains, although they are structurally similar to gram-negative bacteria with two layers. The
Chloroflexota The Chloroflexota are a phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (biology), di ...
have a single layer, yet (with some exceptions) stain negative. Two related phyla to the Chloroflexi, the TM7 clade and the Ktedonobacteria, are also monoderms. Some Bacillota species are not gram-positive. These belong to the class
Mollicutes Mollicutes is a class of bacteria distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin ''mollis'' (meaning "soft" or "pliable"), and ''cutis'' (meaning "skin"). Individuals are very small, typically only 0. ...
(alternatively considered a class of the phylum
Mycoplasmatota Mycoplasmatota is a phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (biology), divisi ...
), which lack peptidoglycan ( gram-indeterminate), and the class Negativicutes, which includes ''
Selenomonas Members of the genus ''Selenomonas'' (motile crescent-shaped bacteria in general) are referred to trivially as selenomonads. The genus ''Selenomonas'' constitutes a group of motile crescent-shaped bacteria and includes species In biology, ...
'' and stain gram-negative. Additionally, a number of bacterial taxa (viz.
Negativicutes The Negativicutes are a class (taxonomy), class of bacteria in the phylum Bacillota, whose members have a peculiar cell wall with a lipopolysaccharide outer membrane which stains gram-negative bacteria, gram-negative, unlike most other members of ...
,
Fusobacteriota Fusobacteriota are obligately anaerobic non-sporeforming Gram-negative Gram-negative bacteria are bacteria that do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. They are cha ...
,
Synergistota The Synergistota is a phylum of anaerobic bacteria that show Gram-negative Gram-negative bacteria are bacteria that do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. They are ...
, 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 GroEL is a protein which belongs to the chaperonin family of Chaperone (protein), molecular chaperones, and is found in many bacteria. It is required for the proper protein folding, folding of many proteins. To function properly, GroEL requires ...
) protein distinguishes all traditional phyla of gram-negative bacteria (e.g.,
Pseudomonadota Pseudomonadota (synonym Proteobacteria) is a major phylum of Gram-negative bacteria. The renaming of phyla in 2021 remains controversial among microbiologists, many of whom continue to use the earlier names of long standing in the literature. The ...
,
Aquificota The ''Aquificota'' phylum (biology), phylum is a diverse collection of bacteria that live in harsh environmental settings. The name ''Aquificota'' was given to this phylum based on an early genus identified within this group, ''Aquifex'' (“wate ...
,
Chlamydiota The Chlamydiota (synonym Chlamydiae) are a bacterial phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany t ...
,
Bacteroidota The phylum (biology), phylum Bacteroidota (synonym Bacteroidetes) is composed of three large classes of Gram-negative bacteria, Gram-negative, nonsporeforming, anaerobic or aerobic, and rod-shaped bacteria that are widely distributed in the envir ...
,
Chlorobiota The green sulfur bacteria are a phylum of obligately anaerobic organism, anaerobic photoautotrophic bacteria that metabolize sulfur. Green sulfur bacteria are motility, nonmotile (except ''Chloroherpeton thalassium'', which may glide) and capabl ...
, "
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum (biology), phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's ...
",
Fibrobacterota Fibrobacterota is a small bacterial phylum (biology), phylum which includes many of the major rumen bacteria, allowing for the degradation of plant-based cellulose in ruminants, ruminant animals. Members of this phylum were categorized in other p ...
,
Verrucomicrobiota Verrucomicrobiota is a phylum of Gram-negative bacteria that contains only a few described species. The species identified have been isolated from fresh water, marine and soil environments and human Feces, faeces. A number of as-yet uncultivated ...
, Planctomycetota,
Spirochaetota A spirochaete () or spirochete is a member of the phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany ...
,
Acidobacteriota Acidobacteriota is a phylum of Gram-negative bacteria. Its members are physiologically diverse and ubiquitous, especially in soils, but are under-represented in culture. Description Members of this phylum are physiologically diverse, and can be ...
, etc.) from these other atypical diderm bacteria, as well as other phyla of monoderm bacteria (e.g.,
Actinomycetota The ''Actinomycetota'' (synonym ''Actinobacteria'') are a phylum of mostly Gram-positive bacteria. They can be terrestrial animal, terrestrial or aquatic animal, aquatic. They are of great economic importance to humans because agriculture and fo ...
,
Bacillota The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have gram-positive bacteria, gram-positive cell wall structure. The renaming of phyla such as Firmicutes in 2021 remains controversial among microbiologists, many of whom ...
,
Thermotogota The Thermotogota are a phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (biology), div ...
,
Chloroflexota The Chloroflexota are a phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (biology), di ...
, etc.). The presence of this CSI in all sequenced species of conventional LPS (
lipopolysaccharide Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the Bacterial ...
)-containing gram-negative bacterial phyla provides evidence that these phyla of bacteria form a monophyletic clade and that no loss of the outer membrane from any species from this group has occurred.


Pathogenicity

In the classical sense, six gram-positive genera are typically pathogenic in humans. Two of these, ''
Streptococcus ''Streptococcus'' is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of bi ...
'' and ''
Staphylococcus ''Staphylococcus'' is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of b ...
'', are
cocci A coccus (plural cocci) is any bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of proka ...
(sphere-shaped). The remaining organisms are
bacilli Bacilli is a taxonomic class of bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typicall ...
(rod-shaped) and can be subdivided based on their ability to form
spore In biology, a spore is a unit of sexual reproduction, sexual or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of ...
s. The non-spore formers are ''
Corynebacterium ''Corynebacterium'' () is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of ...
'' and ''
Listeria ''Listeria'' is a genus of bacteria that acts as an intracellular parasite in mammals. Until 1992, 17 species were known, each containing two subspecies. By 2020, 21 species had been identified. The genus is named in honour of the British pio ...
'' (a coccobacillus), whereas ''
Bacillus ''Bacillus'' (Latin "stick") is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum ''Bacillota'', with 266 named species. The term is also used to describe bacillus (shape), the shape (rod) of other so-shaped bacteria; and the ...
'' and ''
Clostridium ''Clostridium'' is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biolo ...
'' produce spores. The spore-forming bacteria can again be divided based on their
respiration Respiration may refer to: Biology * Cellular respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive ...
: ''Bacillus'' is a
facultative anaerobe A facultative anaerobic organism is an organism In biology, an organism () is any life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (bio ...
, while ''Clostridium'' is an
obligate anaerobe Obligate anaerobes are microorganisms killed by normal Atmosphere of Earth, atmospheric concentrations of oxygen (20.95% O2). Oxygen tolerance varies between species, with some species capable of surviving in up to 8% oxygen, while others lose v ...
. 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 An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmiss ...
in newborn infants. Access provided by the University of Pittsburgh. Novel species of clinically relevant gram-positive bacteria also include '' Catabacter hongkongensis'', which is an emerging pathogen belonging to
Bacillota The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have gram-positive bacteria, gram-positive cell wall structure. The renaming of phyla such as Firmicutes in 2021 remains controversial among microbiologists, many of whom ...
.


Bacterial transformation

Transformation Transformation may refer to: Science and mathematics In biology and medicine * Metamorphosis, the biological process of changing physical form after birth or hatching * Malignant transformation, the process of cells becoming cancerous * Trans ...
is one of three processes for
horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between Unicellular organism, unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offsprin ...
, in which exogenous genetic material passes from a donor bacterium to a recipient bacterium, the other two processes being
conjugation Conjugation or conjugate may refer to: Linguistics *Grammatical conjugation In linguistics Linguistics is the scientific study of human language. It is called a scientific study because it entails a comprehensive, systematic, objectiv ...
(transfer of
genetic material Nucleic acids are biopolymers, macromolecules, essential to all Organism, known forms of life. They are composed of nucleotides, which are the monomers made of three components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. ...
between two bacterial cells in direct contact) and transduction (injection of donor bacterial DNA by a
bacteriophage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek language, Greek φαγεῖν ('), meaning "to d ...
virus into 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 Gram-negative bacteria are bacteria that do not retain the Crystal violet, 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 peptidogly ...
; 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 pneumoniae'', or pneumococcus, is a Gram-positive, spherical bacteria, hemolysis (microbiology), alpha-hemolytic (under aerobic conditions) or beta-hemolytic (under anaerobic conditions), aerotolerant anaerobe, aerotolerant anaero ...
'', ''
Streptococcus mutans ''Streptococcus mutans'' is a Facultative anaerobic organism, facultatively anaerobic, gram-positive coccus (round bacteria, bacterium) commonly found in the human oral cavity and is a significant contributor to dental caries, tooth decay. It is ...
'', ''
Staphylococcus aureus ''Staphylococcus aureus'' is a Gram-positive bacteria, Gram-positive coccus, spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the Respiratory tract, upper respir ...
'' and ''
Streptococcus sanguinis ''Streptococcus sanguinis'', formerly known as ''Streptococcus sanguis'', is a Gram-positive facultative anaerobic coccus species of bacteria and a member of the Streptococcus viridans, Viridans Streptococcus group. ''S. sanguinis'' is a normal ...
'' and in gram-positive soil bacterium ''
Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyst ...
, Bacillus cereus''.


Orthographic note

The adjectives ''Gram-positive'' and ''Gram-negative'' derive from 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 A style guide or manual of style is a set of standards for the writing, formatting, and design of documents. It is often called a style sheet, although that term also has multiple other meanings. The standards can be applied either for gene ...
(e.g., that of the
CDC The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services The United States Department of He ...
), if any, governs the document being written. This is further explained at '' Gram staining § Orthographic note''.


References


External links

*
3D structures of proteins associated with plasma membrane of gram-positive bacteria

3D structures of proteins associated with outer membrane of gram-positive bacteria
{{Authority control Staining Bacteriology