"''

Candidatus In prokaryote nomenclature, ''Candidatus'' (abbreviated ''Ca.''; Latin for "candidate of Roman office") is used to name prokaryotic taxa that are well characterized but yet- uncultured. Contemporary sequencing approaches, such as 16S ribosomal R ...

'' 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, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

bacillus ''Bacillus'', from Latin "bacillus", meaning "little staff, wand", 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-sh ...

bacterium that is a part of the

phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...

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 ...

. "''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 ...

and mutualistic

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

microbe commonly found occupying specialized cell compartments of sap-feeding insects called

bacteriocyte A bacteriocyte ( Greek for ''bacteria cell''), also known as a mycetocyte, is a specialized adipocyte found primarily in certain insects such as aphids, tsetse flies, German cockroaches, weevils, and ants. These cells contain endosymbioti ...

s. 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. Their ...

''. Other studies have documented the nature of its residency in other insects like the maize leafhopper ('' Cicadulina'') or the spittlebug (''

Cercopoidea The superfamily Cercopoidea, some members of which are called froghoppers and still others known as spittlebugs, are a group of hemipteran insects in the suborder Auchenorrhyncha. Adults are capable of jumping many times their height and length, ...

''). "''Ca.'' K. muelleri" is noted for its exceptionally minimal genome 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 an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualism (biology), mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia), whi ...

was found in the dissected

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

Moravia Moravia ( ; ) is a historical region in the eastern Czech Republic, roughly encompassing its territory within the Danube River's drainage basin. It is one of three historical Czech lands, with Bohemia and Czech Silesia. The medieval and early ...

n embryologist who was one of the first scientists to recognize that the insect bacteriome 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 who was awarded the 1946 Nobel Prize in Physiology or Medicine, "for the discovery that mutations can be induced by X-rays". Muller warned of long-term dang ...

) 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 o ...

. "''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 Bacterial cellular morphologies are the shapes that are characteristic of various types of bacteria and often key to their identification. Their direct examination under a light microscope enables the classification of these bacteria (and archae ...

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 of insects, commonly called true bugs, comprising more than 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from ...

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 with another

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

lineage from the taxonomic ''class''

Betaproteobacteria ''Betaproteobacteria'' are a class of Gram-negative bacteria, and one of the six classes of the phylum '' Pseudomonadota'' (synonym Proteobacteria). Metabolism The ''Betaproteobacteria'' comprise over 75 genera and 400 species. Together, they ...

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

vitamin Vitamins are Organic compound, organic molecules (or a set of closely related molecules called vitamer, vitamers) that are essential to an organism in small quantities for proper metabolism, metabolic function. Nutrient#Essential nutrients, ...

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

class Class, Classes, 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 d ...

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

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

'' 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 class of environmental bacteria. It contains the family Flavobacteriaceae, which is the largest family in the phylum Bacteroidota. This class is widely distributed in soil, fresh, and seawater habi ...

. 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 o ...

beta-subunit,

initiation factor In molecular biology, initiation factors are proteins that bind to the small subunit of the ribosome during the initiation of Translation (genetics), translation, a part of protein biosynthesis. Initiation factors can interact with repressors to ...

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 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 ...

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 catalyzes the chemical reactions that synthesize RNA from a DNA template. Using the e ...

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 ...

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 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 resolving paraphyl ...

) places the bacterium under family Blattabacteriaceae. 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 funded large-scale sequencing centers in the United States. Affiliated with Washingt ...

using Illumina dye sequencing. 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. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...

''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 and ...

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 ...

. 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. Pseudogenes can be formed from both protein-coding genes and non-coding genes. In the case of protein-coding genes, most pseudogenes arise as superfluous copies of fun ...

. Of the 227 different

polypeptide Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty ...

s, 99 of them are

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

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 of ...

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 (biology), cell identifies and corrects damage to the DNA molecules that encode its genome. A weakened capacity for DNA repair is a risk factor for the development of cancer. DNA is cons ...

translation Translation is the communication of the semantics, 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 English la ...

cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

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 or 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

Candidatus Sulcia muelleri is an obligate endosymbiont of sap-feeding insects, primarily cicadas and leafhoppers, where it provides essential amino acids missing from their plant sap diet. It often coexists with a secondary symbiont, such as Hodgkinia or Baumannia, which complements its metabolic capabilities. Sulcia muelleri has an extremely reduced genome, averaging around 250 kilobases, losing most regulatory genes due to its dependence on the host environment.McCutcheon, J. P., & Moran, N. A. (2010). Functional convergence in reduced genomes of bacterial symbionts spanning 200 million years of evolution. Genome Biology and Evolution, 2(1), 708-718. https://doi.org/10.1093/gbe/evq054 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 base-pair substitution rate compared to their free-living ancestors. Because of

symbiosis Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biological interaction, between two organisms of different species. The two organisms, termed symbionts, can fo ...

, hosts may be able to utilize

metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell (biology), cell. The reactants, products, and Metabolic intermediate, intermediates of an enzymatic reaction are known as metabolites, which are ...

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 (biology), tissue in vascular plants, the other being phloem; both of these are part of the vascular bundle. The basic function of the xylem is to transport water upward from the roots to parts o ...

and

phloem Phloem (, ) is the living 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 transport process is ...

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. Their ...

. "''Ca.'' K. muelleri" is always found inside the

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 genus-rich taxon of the Prokaryotes. Several medically, ecologically, and scienti ...

, '' Baumannia cicadellinicola''. 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. L-Homoserine is not one of the common amino acids encoded by DNA. It differs from the proteinogenic amino acid serine by insertion of an addit ...

L-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 when dissolved in water), a carboxyl group (which is in the deprotonated −COO− fo ...

. '' Baumannia cicadellinicola'' 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 of 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

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

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 of oxidizing biological fuels using an inorganic electron acceptor, such as oxygen, to drive production of adenosine triphosphate (ATP), which stores chemical energy in a biologically accessible form. Cellu ...

. 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 the mitochondria of eukaryotes. It is the last enzyme in the Cellular respir ...

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

electron donor In chemistry, an electron donor is a chemical entity that transfers electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process. An obsolete definition equated an electron dono ...

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; known as glutamate in its anionic form) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a Essential amino acid, non-essential nutrient for humans, meaning that ...

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 ( ...

and

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

; 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 ade ...

. 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 over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

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 over 500 amino acids exist in nature, by far the most important are the Proteinogenic amino acid, 22 α-amino acids incorporated into p ...

, 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-Car ...

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 deproton ...

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 when dissolved in water), 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 depro ...

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. Lysine contains an α-amino group (which is in the protonated form when the lysine is dissolved in water at physiological pH), an α-carboxylic acid group ( ...

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

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

, 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 aromat ...

. 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 non-essential amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine play ...

and

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

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,

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 ...

-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, the other two being vitamin K1 (phylloquinone) and K3 (menadione). K2 is both a tissue and bacterial product (derived from vitamin K1 in both cases) and is usually found in an ...

. "''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 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