Karelsulcia muelleri

Key takeaways

Karelsulcia muelleri belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Karelsulcia muelleri to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Karelsulcia muelleri from memory before moving on to harder problems.

Reference excerpt

Candidatus Karelsulcia muelleri is an aerobic, gram-negative, bacillus bacterium that is a part of the phylum Bacteroidota. Ca. K. muelleri is an obligate and mutualistic symbiotic 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. Other studies have documented the nature of its residency in other insects like the maize leafhopper (Cicadulina) or the spittlebug (Cercopoidea). Ca. K. muelleri is noted for its exceptionally minimal genome and it is currently identified as having the smallest known sequenced Bacteroidota genome at only 245 kilobases. Various "Ca. Karesulcia" strains have an intimate relationship with plant sap-feeding auchenorrhynchan insects of the order Hemiptera, with the initial symbiotic event dating back to 340 million years ago, providing 8 essential amino acids to the host. The "Ca. Karesulcia" symbioant genome is highly conserved among insects and has co-evolved with the host ever since the initial event.

History and Etymology Ca. K. muelleri was classified under microscope in 2005 by the evolutionary biologist Nancy A. Moran. The endosymbiont was found in the dissected bacteriocyte of the spittlebug (Calstopter arizonana). The genus "Candidatus Sulcia" is named after Karel Šulc, a Moravian 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) who speculated in 1960 that there was a parallel evolutionary history between endosymbionts and a select clade of insect hosts known as Auchenorrhyncha.

Morphology Little has been documented about the morphology of Ca. K. muelleri. Ca. K. muelleri is a rod-shaped bacterium measuring 5–7 μm in length, 0.7 μm in diameter and 2–5 μm in width. Because Ca. K. muelleri lacks most of the genes responsible for cell division 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 Flavobacteriales, Ca. K. muelleri is gram-negative.

Phylogeny The phylogeny of Ca. K. muelleri has been discovered to follow the phylogeny of the Hemiptera clade, Auchenorrhyncha. As of February 2026, the NCBI Genome page lists 195 genomes of "Ca. Karelsulcia". Phylogeny using 120 bacterial markers from known genomes (see GTDB) places the bacterium under family Blattabacteriaceae. Using 67 full genomes of acceptable quality, the database is able to define 7 species-level groups.

"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 tree was constructed by comparing the peptide sequences of ten different types of proteins. The proteins used were the DNA polymerase III beta-subunit, initiation factor IF-2, leucyl-tRNA synthetase, the phenylalanine—tRNA ligase beta-subunit, VARS, elongation factor Tu, the RNA polymerase beta-subunit, and the ribosomal proteins L2, S5, and S11. Where Ca. K. muelleri is found occupying the body of Auchenorrhyncha 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.

Genomics The Ca. K. muelleri, strain GWSS genome was completely sequenced at McDonnell Genome Institute 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's. It is composed of one circular chromosome that measures 245,530 base pairs long. There are neither any plasmids nor any other mobile genetic elements. The genome contains a total of 263 genes: 227 protein genes, 36 RNA genes and one pseudogene. Of the 227 different polypeptides, 99 of them are enzymes and another 9 are transport proteins. The GC-content 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. It has lost most regulatory genes due to its dependence on the host environment.

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, translation or cell membrane biosynthesis. The conditions required for genome reduction 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.

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Worked examples

Example 1 — a first encounter with Karelsulcia muelleri

Start with the simplest possible case. Write down what Karelsulcia muelleri claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Karelsulcia muelleri before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Karelsulcia muelleri ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Karelsulcia muelleri

In research: Karelsulcia muelleri appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Karelsulcia muelleri in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Karelsulcia muelleri is common in secondary-school and first-year university syllabi. It links to neighbouring topics Candidatus taxa, Flavobacteria, so understanding it makes those chapters shorter.
In everyday life: Look for Karelsulcia muelleri outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Karelsulcia muelleri in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Karelsulcia muelleri means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Karelsulcia muelleri out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Karelsulcia muelleri in simple terms?

Candidatus Karelsulcia muelleri is an aerobic, gram-negative, bacillus bacterium that is a part of the phylum Bacteroidota. Ca.

Why does Karelsulcia muelleri matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Karelsulcia muelleri?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Karelsulcia muelleri.