Firmicutes
Encyclopedia
The Firmicutes are a phylum of bacteria
, most of which have Gram-positive cell wall
structure. A few, however, such as Megasphaera, Pectinatus
, Selenomonas and Zymophilus
, have a porous pseudo-outer-membrane that causes them to stain Gram-negative. Scientists once classified the Firmicutes to include all Gram-positive bacteria, but have recently defined them to be of a core group of related forms called the low-G+C
group, in contrast to the Actinobacteria
. They have round cells, called cocci (singular coccus), or rod-shaped forms.
Many Firmicutes produce endospore
s, which are resistant to desiccation
and can survive extreme conditions. They are found in various environments, and the group includes some notable pathogens. Those in one family, the heliobacteria
, produce energy through photosynthesis
. Firmicutes play an important role in beer, wine, and cider spoilage.
, which are anaerobic
, the Bacilli
, which are obligate or facultative aerobes, and the Mollicutes
.
On phylogenetic tree
s, the first two groups show up as paraphyletic or polyphyletic, as do their main genera, Clostridium
and Bacillus
.
Bacilli, order Bacillales
Bacilli, order Lactobacillales
Clostridia
Erysipelotrichi
has been shown to be involved in energy resorption and obesity.
exchange across species and genera, the presence of Firmicutes can now be detected by real-time PCR using the methodologies recently described.
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, most of which have Gram-positive cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
structure. A few, however, such as Megasphaera, Pectinatus
Pectinatus
Pectinatus is a genus of Firmicutes bacteria classified within the class Negativicutes....
, Selenomonas and Zymophilus
Zymophilus
Zymophilus is a genus of Firmicutes bacteria classified within the class Negativicutes....
, have a porous pseudo-outer-membrane that causes them to stain Gram-negative. Scientists once classified the Firmicutes to include all Gram-positive bacteria, but have recently defined them to be of a core group of related forms called the low-G+C
GC-content
In molecular biology and genetics, GC-content is the percentage of nitrogenous bases on a DNA molecule that are either guanine or cytosine . This may refer to a specific fragment of DNA or RNA, or that of the whole genome...
group, in contrast to the Actinobacteria
Actinobacteria
Actinobacteria are a group of Gram-positive bacteria with high guanine and cytosine content. They can be terrestrial or aquatic. Actinobacteria is one of the dominant phyla of the bacteria....
. They have round cells, called cocci (singular coccus), or rod-shaped forms.
Many Firmicutes produce endospore
Endospore
An endospore is a dormant, tough, and temporarily non-reproductive structure produced by certain bacteria from the Firmicute phylum. The name "endospore" is suggestive of a spore or seed-like form , but it is not a true spore . It is a stripped-down, dormant form to which the bacterium can reduce...
s, which are resistant to desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
and can survive extreme conditions. They are found in various environments, and the group includes some notable pathogens. Those in one family, the heliobacteria
Heliobacteria
The heliobacteria are phototrophic, that is to say, they convert light energy into chemical energy by photosynthesis; they use a PSI type reaction center. The primary pigment involved is bacteriochlorophyll g, which is unique to the group and has a unique absorption spectrum; this gives the...
, produce energy through photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
. Firmicutes play an important role in beer, wine, and cider spoilage.
Classes
The group is typically divided into the ClostridiaClostridia
The Clostridia are a class of Firmicutes, including Clostridium and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them. Species of the genus Clostridium are all Gram-positive and have the ability to...
, which are anaerobic
Anaerobic organism
An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present...
, the Bacilli
Bacilli
Bacilli refers to a taxonomic class of bacteria. It includes two orders, Bacillales and Lactobacillales, which contain several well-known pathogens like Bacillus anthracis .-Ambiguity:...
, which are obligate or facultative aerobes, and the Mollicutes
Mollicutes
The Mollicutes are a class of bacteria distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin mollis , and cutis . They are parasites of various animals and plants, living on or in the host's cells. Individuals are very small, typically only 0.2–0.3 μm in size...
.
On phylogenetic tree
Phylogenetic tree
A phylogenetic tree or evolutionary tree is a branching diagram or "tree" showing the inferred evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical and/or genetic characteristics...
s, the first two groups show up as paraphyletic or polyphyletic, as do their main genera, Clostridium
Clostridium
Clostridium is a genus of Gram-positive bacteria, belonging to the Firmicutes. They are obligate anaerobes capable of producing endospores. Individual cells are rod-shaped, which gives them their name, from the Greek kloster or spindle...
and Bacillus
Bacillus
Bacillus is a genus of Gram-positive, rod-shaped bacteria and a member of the division Firmicutes. Bacillus species can be obligate aerobes or facultative anaerobes, and test positive for the enzyme catalase. Ubiquitous in nature, Bacillus includes both free-living and pathogenic species...
.
Genera
While there are currently more than 274 genera within the Firmicutes phylum, notable genera of Firmicutes include:Bacilli, order Bacillales
Bacillales
The Bacillales are an order of Gram-positive bacteria, placed within the Firmicutes. Representative genera include Bacillus, Listeria and Staphylococcus....
- BacillusBacillusBacillus is a genus of Gram-positive, rod-shaped bacteria and a member of the division Firmicutes. Bacillus species can be obligate aerobes or facultative anaerobes, and test positive for the enzyme catalase. Ubiquitous in nature, Bacillus includes both free-living and pathogenic species...
- Listeria
- StaphylococcusStaphylococcusStaphylococcus is a genus of Gram-positive bacteria. Under the microscope they appear round , and form in grape-like clusters....
Bacilli, order Lactobacillales
Lactobacillales
The Lactobacillales are an order of Gram-positive bacteria that comprise the lactic acid bacteria. They are widespread in nature, and are found in soil, water, plants and animals. They are widely used in the production of fermented foods, including dairy products such as yogurt, cheese, butter,...
- EnterococcusEnterococcusEnterococcus is a genus of lactic acid bacteria of the phylum Firmicutes. Enterococci are Gram-positive cocci that often occur in pairs or short chains, and are difficult to distinguish from streptococci on physical characteristics alone. Two species are common commensal organisms in the...
- LactobacillusLactobacillusLactobacillus is a genus of Gram-positive facultative anaerobic or microaerophilic rod-shaped bacteria. They are a major part of the lactic acid bacteria group, named as such because most of its members convert lactose and other sugars to lactic acid. They are common and usually benign...
- LactococcusLactococcusLactococcus is a genus of lactic acid bacteria that were formerly included in the genus Streptococcus Group N1. They are known as homofermentors meaning that they produce a single product, lactic acid in this case, as the major or only product of glucose fermentation...
- LeuconostocLeuconostocLeuconostoc is a genus of Gram-positive bacteria, placed within the family of Leuconostocaceae. They are generally ovoid cocci often forming chains. Leuconostoc spp. are intrinsically resistant to vancomycin and are catalase-negative . All species within this genus are heterofermentative and are...
- PediococcusPediococcusPediococcus is a genus of Gram-positive lactic acid bacteria, placed within the family of Lactobacillaceae. They usually occur in pairs or tetrads, and divide along two planes of symmetry, as do the other lactic acid cocci genera Aerococcus and Tetragenococcus. They are purely homofermentative...
- StreptococcusStreptococcusStreptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...
Clostridia
Clostridia
The Clostridia are a class of Firmicutes, including Clostridium and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them. Species of the genus Clostridium are all Gram-positive and have the ability to...
- AcetobacteriumAcetobacteriumAcetobacterium is a genus of gram-positive bacteria which belong to the Eubacteriaceae family. Usually they are homoacetogens, which means they predominantly produce acetic acid as a metabolic by-product. Not to be confused with acetic acid bacteria which are aerobic, gram-negative...
- ClostridiumClostridiumClostridium is a genus of Gram-positive bacteria, belonging to the Firmicutes. They are obligate anaerobes capable of producing endospores. Individual cells are rod-shaped, which gives them their name, from the Greek kloster or spindle...
- Eubacterium
- Heliobacterium
- Heliospirillum
- Megasphaera
- PectinatusPectinatusPectinatus is a genus of Firmicutes bacteria classified within the class Negativicutes....
- Selenomonas
- ZymophilusZymophilusZymophilus is a genus of Firmicutes bacteria classified within the class Negativicutes....
- SporohalobacterSporohalobacterSporohalobacter are a genus of anaerobic bacteria belonging to the family Haloanaerobiaceae. The organisms are spore-forming bacteria that grow in hypersaline environments....
- SporomusaSporomusaSporomusa is a genus of Firmicutes bacteria classified within the class Negativicutes.-Phylogeny:The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature and the phylogeny is based on 16S rRNA-based LTP release 106 by The All-Species Living Tree...
Erysipelotrichi
- ErysipelothrixErysipelothrix rhusiopathiaeErysipelothrix rhusiopathiae is a gram-positive, catalase-negative, rod-shaped bacterium. It grows aerobically and anaerobically and does not contain endotoxin. Distributed worldwide, E. rhusiopathiae is primarily considered an animal pathogen, causing a disease known as erysipelas in animals...
Health implications
Firmicutes make up the largest portion of the mouse and human gut microbiome. The division Firmicutes as part of the gut floraGut flora
Gut flora consists of microorganisms that live in the digestive tracts of animals and is the largest reservoir of human flora. In this context, gut is synonymous with intestinal, and flora with microbiota and microflora....
has been shown to be involved in energy resorption and obesity.
Laboratory detection
While there has up to this point in time not been a way to categorically define a given bacterium as belonging to Firmicutes, as the phylum is highly diverse in phenotypic characteristics due to its members' promiscuous plasmidPlasmid
In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...
exchange across species and genera, the presence of Firmicutes can now be detected by real-time PCR using the methodologies recently described.
External links
- Phylum "Firmicutes" - J.P. Euzéby: List of Prokaryotic names with Standing in Nomenclature