"''

Candidatus In prokaryote nomenclature, ''Candidatus'' (Latin for candidate of Roman office) is used to name prokaryotic phyla that are well characterized but yet-uncultured. Contemporary sequencing approaches, such as 16S sequencing or metagenomics, provide m ...

'' Karelsulcia muelleri" is an

aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cellu ...

gram-negative 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 ...

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 the shape (rod) of other so-shaped bacteria; and the plural ''Bacilli ...

bacterium that is a part of the

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

Bacteroidota The phylum Bacteroidota (synonym Bacteroidetes) is composed of three large classes of Gram-negative, nonsporeforming, anaerobic or aerobic, and rod-shaped bacteria that are widely distributed in the environment, including in soil, sediments, and ...

. "''Ca.'' K. muelleri" is an

obligate {{wiktionary, obligate As an adjective, obligate means "by necessity" (antonym ''facultative'') and is used mainly in biology in phrases such as: * Obligate aerobe, an organism that cannot survive without oxygen * Obligate anaerobe, an organism that ...

and mutualistic

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

microbe commonly found occupying specialized cell compartments of sap-feeding insects called bacteriocytes. A majority of the research done on "''Ca.'' K. muelleri" has detailed its relationship with the host ''

Homalodisca vitripennis The glassy-winged sharpshooter (''Homalodisca vitripennis'', formerly known as ''H. coagulata'') is a large leafhopper (family Cicadellidae), similar to other species of sharpshooter. Description These sharpshooters are about in length. Thei ...

''. Other studies have documented the nature of its residency in other insects like the

maize leafhopper ''Cicadulina mbila'', the maize leafhopper, is a leafhopper species in the genus ''Cicadulina''. It is found in sub-Saharan Africa (Kenya, Tanzania and Uganda), the Middle East, West Asia and India. It is one of the vectors of the maize streak ...

(''

Cicadulina ''Cicadulina'' is a leafhopper genus in the tribe Macrostelini. ''Cicadulina'' species are vectors of the maize streak virus, a disease which is a sporadic but severe in sub-Saharan Africa. The cause is a geminivirus which is persistently tran ...

'') or the spittlebug ('' Cercopoidea''). "''Ca.'' K. muelleri" is noted for its exceptionally

minimal genome Minimal may refer to: * Minimal (music genre), art music that employs limited or minimal musical materials * "Minimal" (song), 2006 song by Pet Shop Boys * Minimal (supermarket) or miniMAL, a former supermarket chain in Germany and Poland * Minim ...

and it is currently identified as having the smallest known sequenced

genome at only 245 kilobases.

Discovery

"''Ca.'' K. muelleri" was classified under microscope in 2005 by the evolutionary biologist Nancy A. Moran. The

endosymbiont An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within" ...

was found in the dissected bacteriocyte of the spittlebug (''Calstopter arizonana''). The genus "''Candidatus'' Sulcia" is named after Vytváření Karel Šulc, a

Moravia Moravia ( , also , ; cs, Morava ; german: link=yes, Mähren ; pl, Morawy ; szl, Morawa; la, Moravia) is a historical region in the east of the Czech Republic and one of three historical Czech lands, with Bohemia and Czech Silesia. The me ...

n embryologist who was one of the first scientists to recognize that the insect

bacteriome A bacteriome is a specialized organ, found mainly in some insects, that hosts endosymbiotic bacteria. Bacteriomes contain specialized cells, called bacteriocytes, that provide nutrients and shelter to the bacteria while protecting the host animal ...

is an organ where bacteria reside. The name was amended to "''Ca.'' Karelsulcia" in 2017 to avoid breach of the nomenclatural code, as ''Sulcia'' is already a genus of spiders. The species, ''muelleri'', has been named in the honor of H. J. Müller, (not to be confused with

Hermann Joseph Muller Hermann Joseph Muller (December 21, 1890 – April 5, 1967) was an American geneticist, educator, and Nobel laureate best known for his work on the physiological and genetic effects of radiation (mutagenesis), as well as his outspoken political ...

) who speculated in 1960 that there was a parallel evolutionary history between endosymbionts and a select clade of insect hosts known as

Auchenorrhyncha The Auchenorrhyncha suborder of the Hemiptera contains most of the familiar members of what was called the "Homoptera" – groups such as cicadas, leafhoppers, treehoppers, planthoppers, and spittlebugs. The aphids and scale insects are the ot ...

. "''Ca.'' K. muelleri" is a member of the order

Flavobacteriales The order Flavobacteriales comprises several families of environmental bacteria. Comparative genomics and molecular signatures ''Flavobacteriales'' is of one of the orders from the phylum ''Bacteroidota''. Comparative genomic studies have ident ...

. It is currently not classified as a member of any taxonomic family.

Morphology

Little has been documented about the morphology of "''Ca.'' K. muelleri". "''Ca.'' K. muelleri" is a

rod-shaped A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name ''Bacillu ...

bacterium measuring 5–7 μm in length, .7 μm in diameter and 2–5 μm in width. Because "''Ca.'' K. muelleri" lacks most of the genes responsible for

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

and membrane synthesis, it is sometimes observed to extend to unusual lengths of up to 100 μm during part of its life cycle. Like all other

, "''Ca.'' K. muelleri" is

Phylogeny

The phylogeny of "''Ca.'' K. muelleri" has been discovered to follow the phylogeny of the

Hemiptera Hemiptera (; ) is an order (biology), order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, Reduviidae, assassin bugs, Cimex, bed bugs, and shield bugs. ...

clade,

. The first association between "''Ca.'' K. muelleri" and Auchenorrhyncha is estimated to have occurred sometime between 260 and 280 million years ago. Further evidence supports the idea that "''Ca.'' K. muelleri" has

coevolved In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well ...

with another

lineage from the taxonomic ''class''

Betaproteobacteria Betaproteobacteria are a class of Gram-negative bacteria, and one of the eight classes of the phylum Pseudomonadota (synonym Proteobacteria). The ''Betaproteobacteria'' are a class comprising over 75 genera and 400 species of bacteria. Togeth ...

. The result of this coevolution can be noticed through the fact that both "''Ca.'' K. muelleri" and its host leave cofactor and

vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an Nutrient#Essential nutrients, essential micronutrient that an organism needs in small quantities for the proper functioning of its ...

production to another member of the symbiotic relationship. Although the co-residents of "''Ca.'' K. muelleri" are not always of the

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

Betaproteobacteria, contemporary analyses have shown that they often are. The Betaproteobacteria ancestor is suggested to have diversified into the

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

'' Zinderia'', '' Nasuia'' and '' Vidania''. There are currently 9 unique strains of "''Ca.'' K. muelleri" that have been identified through a complete genome sequence. They can all be found here.

"''Candidatus'' Karelsulcia" and the Flavobacteria

The tree below demonstrates the position of "''Ca.'' K. muelleri" with respect to some other members of the class

Flavobacteriia The class Flavobacteriia is composed of a single order of environmental bacteria. According to Bernardet ''et al''., Flavobacteriia are Gram-negative aerobic rods, 2–5 μm long, 0.3–0.5 μm wide, with rounded or tapered end ...

. The tree was constructed by comparing the peptide sequences of ten different types of proteins. The proteins used were the

DNA polymerase III DNA polymerase III holoenzyme is the primary enzyme complex involved in prokaryotic DNA replication. It was discovered by Thomas Kornberg (son of Arthur Kornberg) and Malcolm Gefter in 1970. The complex has high processivity (i.e. the number of ...

beta-subunit,

initiation factor Initiation factors are proteins that bind to the small subunit of the ribosome during the initiation of translation, a part of protein biosynthesis. Initiation factors can interact with repressors to slow down or prevent translation. They have t ...

IF-2,

leucyl-tRNA synthetase Leucyl-tRNA synthetase, cytoplasmic is an enzyme that in humans is encoded by the ''LARS'' gene. Function This gene encodes a cytosolic leucine-tRNA synthetase, a member of the class I aminoacyl-tRNA synthetase family. The encoded enzyme catal ...

, the

phenylalanine—tRNA ligase In enzymology, a phenylalanine—tRNA ligase () is an enzyme that catalyzes the chemical reaction :ATP + L-phenylalanine + tRNAPhe \rightleftharpoons AMP + diphosphate + L-phenylalanyl-tRNAPhe The 3 substrates of this enzyme are ATP, L-phenyl ...

beta-subunit, VARS,

elongation factor Elongation factors are a set of proteins that function at the ribosome, during protein synthesis, to facilitate translational elongation from the formation of the first to the last peptide bond of a growing polypeptide. Most common elongation f ...

Tu, the

RNA polymerase In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that synthesizes RNA from a DNA template. Using the enzyme helicase, RNAP locally opens the ...

beta-subunit, and the

ribosomal protein A ribosomal protein (r-protein or rProtein) is any of the proteins that, in conjunction with rRNA, make up the ribosomal subunits involved in the cellular process of translation. ''E. coli'', other bacteria and Archaea have a 30S small subunit an ...

s L2, S5, and S11. Where "''Ca.'' K. muelleri" is found occupying the body of

hosts, the other members of Flavobacteriia are found residing in freshwater bodies and soils. The inference for the long, isolated stretch of the "''Ca.'' K. muelleri" branch is that there has been a high frequency of

base-pair substitution A point mutation is a genetic mutation where a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence of an organism's genome. Point mutations have a variety of effects on the downstream protein product—consequence ...

which has led to noticeable genetic differences between "''Ca.'' K. muelleri" and most other Flavobacteriia. Phylogeny using 120 bacterial markers from known genomes (see

GTDB The Genome Taxonomy Database (GTDB) is an online database that maintains information on a proposed nomenclature of prokaryotes, following a phylogenomic approach based on a set of conserved single-copy proteins. In addition to breaking up parap ...

) place the bacterium under family

Blattabacteriaceae ''Blattabacterium'' is a genus of obligate mutualistic endosymbiont bacteria that are believed to inhabit all species of cockroach studied to date, with the exception of the genus '' Nocticola''. The genus' presence in the termite ''Mastoterme ...

. Using 11 full genomes of acceptable quality, the database is able to define two species-level groups.

Genomics

The "''Ca.'' K. muelleri", strain GWSS genome was completely sequenced at

McDonnell Genome Institute McDonnell Genome Institute (The Elizabeth H. and James S. McDonnell III Genome Institute) at Washington University in St. Louis, Missouri, is one of three Nih, NIH funded large-scale sequencing centers in the United States. Affiliated with Washing ...

using

Illumina dye sequencing Illumina dye sequencing is a technique used to determine the series of base pairs in DNA, also known as DNA sequencing. The reversible terminated chemistry concept was invented by Bruno Canard and Simon Sarfati at the Pasteur Institute in Paris. I ...

. The genome is an exceptionally reduced genome, where the genetic range of "''Ca.'' K. muelleri" is only 10% of that of ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

''s. It is composed of one circular chromosome that measures 245,530 kilobases long. There are neither any

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...

s nor any other

mobile genetic elements Mobile genetic elements (MGEs) sometimes called selfish genetic elements are a type of genetic material that can move around within a genome, or that can be transferred from one species or replicon to another. MGEs are found in all organisms. In h ...

. The genome contains a total of 263 genes: 227 protein genes, 36 RNA genes and one

pseudogene Pseudogenes are nonfunctional segments of DNA that resemble functional genes. Most arise as superfluous copies of functional genes, either directly by DNA duplication or indirectly by Reverse transcriptase, reverse transcription of an mRNA trans ...

. Of the 227 different

polypeptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A p ...

s, 99 of them are

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

s and another 9 are

transport protein A transport protein (variously referred to as a transmembrane pump, transporter, escort protein, acid transport protein, cation transport protein, or anion transport protein) is a protein that serves the function of moving other materials within ...

s. The

GC-content In molecular biology and genetics, GC-content (or guanine-cytosine content) is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine (G) or cytosine (C). This measure indicates the proportion of G and C bases out o ...

is 22.4%. A distinct feature of the "''Ca.'' K. muelleri" genome is the presence of three unique rRNA sequences at the positions of (486-504), (1001-1016), (1418-1431). The implications of these unique sequences are not identified.

Reduced genome

The "''Ca.'' K. muelleri" genome is what scientists refer to as a reduced genome; it is categorized by the apparent evolutionary loss of many ostensibly essential genes related to processes like

DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...

translation Translation is the communication of the Meaning (linguistic), meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. 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 biological membrane that separates and protects the interior of all cells from the outside environment ( ...

biosynthesis. The conditions required for

genome reduction Genome size is the total amount of DNA contained within one copy of a single complete genome. It is typically measured in terms of mass in picograms (trillionths (10−12) of a gram, abbreviated pg) or less frequently in daltons, or as the total ...

can be multifaceted, however they often involve some form of stability. The occurrence of genome reduction raises interesting questions about what the minimal requirements for a functioning genome are. Scientists are currently testing their hypotheses about the matter by engineering their own reduced genomes.

Symbiosis

"''Ca.'' K. muelleri" is a

symbiont Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

for a group of insects classified under the suborder

. Usual hosts are

cicada The cicadas () are a superfamily, the Cicadoidea, of insects in the order Hemiptera (true bugs). They are in the suborder Auchenorrhyncha, along with smaller jumping bugs such as leafhoppers and froghoppers. The superfamily is divided into two ...

leafhopper A leafhopper is the common name for any species from the family Cicadellidae. These minute insects, colloquially known as hoppers, are plant feeders that suck plant sap from grass, shrubs, or trees. Their hind legs are modified for jumping, and a ...

treehopper Treehoppers (more precisely typical treehoppers to distinguish them from the Aetalionidae) and thorn bugs are members of the family (biology), family Membracidae, a group of insects related to the cicadas and the leafhoppers. About 3,200 species ...

spittlebugs The froghoppers, or the superfamily Cercopoidea, are a group of hemipteran insects in the suborder Auchenorrhyncha. Adults are capable of jumping many times their height and length, giving the group their common name, but they are best known ...

, and

planthopper A planthopper is any insect in the infraorder Fulgoromorpha, in the suborder Auchenorrhyncha, a group exceeding 12,500 described species worldwide. The name comes from their remarkable resemblance to leaves and other plants of their environment ...

s. "''Ca.'' K. muelleri" is always found co-residing its host with another bacterial endosymbiont from the phylum

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 ...

. For example, "''Ca.'' K. muelleri" and "''

'' Zinderia insecticola" are both found to live in the

of select species of the spittlebug. Insect-associated symbionts have been found to share a similar set of features. All symbionts appear to possess a reduced genome, have a high

and bear a more frequent

rate compared to their free-living ancestors. Because of

symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

, hosts may be able to utilize

metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical reac ...

s they might not be able to use if their endosymbionts were absent; one relevant example is the ability for sap-feeding insects to survive off of relatively nutrient-poor food sources, e.g.

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...

and

phloem Phloem (, ) is the living biological tissue, tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This tran ...

Symbiosis with the glassy-winged sharpshooter

Most of the contemporary research concerning the nature of the symbiosis between "''Ca.'' K. muelleri" and its hosts has been conducted on the

glassy-winged sharpshooter The glassy-winged sharpshooter (''Homalodisca vitripennis'', formerly known as ''H. coagulata'') is a large leafhopper (family Cicadellidae), similar to other species of sharpshooter. Description These sharpshooters are about in length. Thei ...

. "''Ca.'' K. muelleri" is always found inside the bacteriocyte of a host along with at least one other endosymbiont; The GSWW strain of "''Ca.'' K. muelleri" is found within the glassy-winged sharpshooter along with the

Gammaproteobacterium Gammaproteobacteria is a class of bacteria in the phylum Pseudomonadota (synonym Proteobacteria). It contains about 250 genera, which makes it the most genera-rich taxon of the Prokaryotes. Several medically, ecologically, and scientifically im ...

, ''

Baumannia cicadellinicola ''Baumannia'' can refer to: * Candidatus ''Baumannia'', a candidatus genus of bacteria including Ca. '' Baumannia cicadellinicola'' * ''Knoxia ''Knoxia'' is a genus of flowering plants in the family Rubiaceae The Rubiaceae are a family of ...

''. Genomic analysis has revealed the respective metabolic roles for each other members of this symbiotic triangle. The glassy-winged sharpshooter, which feeds on the xylem of plants, supplies simple amino acids and carbon sources for the two endosymbionts. In return, "''Ca.'' K. muelleri" uses the basic materials to synthesize complex amino acids like

homoserine Homoserine (also called isothreonine) is an α-amino acid with the chemical formula HO2CCH(NH2)CH2CH2OH. -Homoserine is not one of the common amino acids encoded by DNA. It differs from the proteinogenic amino acid serine by insertion of an additi ...

or L-threonine. ''

'' is reported to provide most of the cofactors and vitamins for the system. One unanswered question about this symbiotic relationship asks how the endosymbionts receive a sufficient amount nitrogen. This speculation arises due to the dilute and nutrient-poor character of xylem. Although

nitrogen assimilation Nitrogen assimilation is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in the environment. Organisms like plants, fungi and certain bacteria that can fix nitrogen gas (N2) depend on the abil ...

was hypothesized, genomic analysis suggests that "''Ca.'' K. muelleri" lacks the ability to perform this function.

Metabolic exchange

Listed below is a model of the symbiotic metabolic exchange based on the

metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...

s that are used by "''Ca.'' K. muelleri" and the metabolites that are produced by "''Ca.'' K. muelleri". The glassy-winged sharpshooter is mostly responsible for providing "''Ca.'' K. muelleri" with nutrients and basic amino acids received from the xylem it feeds on. "''Ca.'' K. muelleri", in return, produces more complex substrates.

Biology and metabolism

"''Ca.'' K. muelleri" is found in the bacteriocytes of their insect hosts. The only time when the bacterial cells are not found in the bacteriocyte compartments is when they are transferred vertically from the host to their host's offspring. Evidence suggests that "''Ca.'' K. muelleri" utilizes

aerobic 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 the bulk production of ATP. Cellular respiration may be des ...

. ATP is synthesized by way of a

cytochrome c oxidase The enzyme cytochrome c oxidase or Complex IV, (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and mitochondria of eukaryotes. It is the last enzyme in the respiratory electr ...

catalyzed termination. The cytochrome is of the type ''cbb-3''. The

electron donor In chemistry, an electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process. Typical reducing agents undergo permanent chem ...

for "''Ca.'' K. muelleri" is implied to be some carbon source retrieved from the sap-feeding diet of its host. Some examples are

glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can syn ...

malate Malic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms (L ...

and

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

; all of which are found in xylem sap. The symbiont harvests reducing power in the form of

NADH Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an aden ...

. The analysis of "''Ca.'' K. muelleri", strain GWSS's reduced genome suggests that a proportionate amount of the genes preserved over its evolution are dedicated to

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

biosynthesis. 21.3% of its protein-coding genes are dedicated to creating

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

, while another 33% is dedicated to

-related processes. "''Ca.'' K. muelleri" is usually capable of synthesizing 8 of its essential amino acids:

leucine Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α- ca ...

valine Valine (symbol Val or V) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α- carboxylic acid group (which is in the deprotonat ...

threonine Threonine (symbol Thr or T) is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), a carboxyl group (which is in the deprotonated −COO� ...

isoleucine Isoleucine (symbol Ile or I) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid group (which is in the deprot ...

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −C ...

arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) and both the am ...

phenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the formula . It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine. This essential amino a ...

, and

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α- carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...

. Some strains of "''Ca.'' K. muelleri" are incapable of making the amino acid,

. It receives its other two amino acids –

methionine Methionine (symbol Met or M) () is an essential amino acid in humans. As the precursor of other amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine plays a critical ro ...

and

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH3+ form under biological conditions), a carboxylic acid group (which is in the de ...

from either its host or its co-symbiont. ''Sulcia muelleri'' is responsible for making two complex amino acids for its host:

and 2-ketovaline. "''Ca.'' K. muelleri" lacks a full set of Aminoacyl tRNA synthetases; surprisingly, however, it possesses all of the genes necessary to code for all 20 amino acids. Other proteins that "''Ca.'' K. muelleri" makes include a couple of

transport proteins A transport protein (variously referred to as a transmembrane pump, transporter, escort protein, acid transport protein, cation transport protein, or anion transport protein) is a protein that serves the function of moving other materials within ...

; the microbe creates

organic cation transport proteins An organic cation transport protein mediates the transport of organic cations across the cell membrane. These proteins are members of the solute carrier family, subfamily 22. This family of proteins can also transport zwitterions and anions, tho ...

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...

-related transporters and heavy-metal ion transporters. "''Ca.'' K. muelleri" is marked down for containing only two genes dedicated to cofactor or vitamin production; these genes code for the synthesis of

menaquinone Vitamin K2 or menaquinone (MK) () is one of three types of vitamin K Vitamin K refers to structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis ...

. "''Ca.'' K. muelleri" receives most of its cofactors or vitamins from its cosymbiont. "''Ca.'' K. muelleri" has a minimal set of genes assigned for DNA housekeeping purposes. The only genes it has for DNA repair are the ''mutL'' and

mutS MutS is a mismatch DNA repair protein, originally described in ''Escherichia coli''. Mismatch repair contributes to the overall fidelity of DNA replication and is essential for combating the adverse effects of damage to the genome. It involves th ...

genes.

References

External links

KeggGenome
- A list of all of the currently sequenced strains of "''Ca.'' K. muelleri"
Uniprot.Org
- A list some currently sequenced strains of "''Ca.'' K. muelleri"
BioCyc.Org
- An overview of the complete and sequenced genome of "''Ca.'' K. muelleri", strain GWSS {{Taxonbar, from=Q20721423 Flavobacteria Candidatus taxa