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Bacterial host range describes the hosts in which a specified bacterial strain can establish a defined biological interaction, such as sustained colonization or disease. The endpoint must be stated: detecting the bacterium, observing growth and measuring host damage are different observations. In plant-pathogen classification, a pathovar summarizes disease-response characteristics in one or more hosts.^[ref]

Pseudomonas syringae pv. tomato DC3000 provides a concrete example of a label that does not enumerate the complete range. Its genome paper identifies both tomato and Arabidopsis thaliana as susceptible hosts.^[ref] The pathovar word tomato therefore cannot be interpreted as an exclusive host list.

For a hypothetical three-host panel, strain X gives the chosen response in hosts A and B, while strain Y does so in hosts A and C. Both have two positive hosts, yet their tested ranges differ; counting positives discards which hosts they were. An untested host D remains unclassified by this panel. Even a negative observation is conditional on the readout and setting.

A 2011 experiment illustrates that context: prior colonization by some Sphingomonas strains reduced DC3000 growth and disease symptoms in Arabidopsis thaliana.^[ref] A changed disease outcome in one host need not imply a change in host identity or a newly established species-wide host boundary.

A bacterial strain is a maintained lineage of bacteria descended from a particular isolation in pure culture. It is more specific than a species name. The naming code describes descent from an isolation and subsequent cultures; it does not require every cell forever to retain an identical genome.^[ref]

A concrete example is Pm70, the avian isolate used for the published Pasteurella multocida genome. Naming both the species and the strain identifies the particular material behind a sequence or assay. The 2001 genome paper reported 2,014 predicted coding sequences for Pm70, not a measurement of every member of the species.^[ref]

For an illustrative experiment, compare a parent strain with a derivative in which one candidate gene has been removed, keeping culture conditions comparable. A change in the measured phenotype tests a claim about that derivative under those conditions. It does not make the two cultures different species, nor establish that all other strains would respond identically.

A useful laboratory record therefore connects the strain designation, source culture and any deliberate genetic changes. Otherwise two reports can use the same species name while testing materially different biological preparations.

Methylobacterium is a taxonomic genus of bacteria whose type species is Methylobacterium organophilum.^[ref] The 1976 genus description concerned pink, rod-shaped isolates and emphasized facultative methylotrophy: using one-carbon compounds while also being able to grow with more complex organic carbon sources. That is a description of the original isolates, not a promise that every bacterial strain subsequently assigned to Methylobacterium has identical physiology.^[ref]

Plant experiments show why identifying the genus is only a starting point. In 2011, researchers established candidate bacterial colonists on Arabidopsis thaliana, then tested their effects during challenge by Pseudomonas syringae pv. tomato DC3000. The tested Methylobacterium strains did not reduce disease development, whereas some Sphingomonas isolates did.^[ref]

The negative result distinguishes presence from protective function. Detecting a Methylobacterium sequence on a healthy leaf does not establish that the bacterium caused the leaf to remain healthy. Testing that idea needs a controlled comparison with a specified strain, host and outcome. Equally, failure to protect in this experiment does not rule out other interactions in different biological settings.

Methylobacterium radiotolerans is a species of bacteria within Methylobacterium. Its type strain has deposits including DSM1819, ATCC27329 and JCM2831. The organism was originally named Pseudomonas radiora; the accepted combination and corrected epithet place it in Methylobacterium. The epithet refers to tolerating radiation.^[ref]

A radiation-related name does not itself supply a survival curve. In an invented measurement, suppose a specified exposure leaves $2\times 10^5$ recoverable colony-forming units from an initially comparable $10^6$. The measured fraction is $2\times 10^5/10^6=0.2$, or 20 percent. Comparing organisms requires a stated bacterial strain, exposure and recovery readout; a single species adjective cannot fix those conditions or identify a universal resistance threshold. These numbers illustrate the measurement, not observed values for this species.

Reference-culture identity also matters when interpreting molecular data. LPSN notes that the older deposit DSM760, once associated with Methylobacterium organophilum, represents Methylobacterium radiotolerans.^[ref] A genome comparison based on an incorrect label could therefore attribute between-species differences to variation within one species. The name, maintained strain and measured phenotype are complementary pieces of a reproducible record.

Methylorubrum extorquens is a species of bacteria and the type species of Methylorubrum. The older combination Methylobacterium extorquens names the same species: LPSN records it as a homotypic synonym, meaning that the two names share a nomenclatural type.^[ref] Experimental results still need a specified bacterial strain; a species name alone does not identify every tested culture.

Methylorubrum extorquens AM1 is a model for facultative methylotrophy. Its studied pathway converts methanol to formaldehyde, with carbon subsequently divided between oxidation toward carbon dioxide and carbon assimilation into cellular material.^[ref]

A 2005 experiment compared AM1-derived mutants with a reference strain during colonization of Medicago truncatula. Mutants defective in methylotrophy lost ground in competition, yet could reach comparable populations when tested separately. This distinction supports a competitive advantage from methanol use without making it the only usable carbon source.^[ref] In an illustrative count, a population share changing from $1/2$ to $1/4$ halves the strain's share; it does not show that its absolute number of cells halved. Both the fraction and the total count are needed to distinguish relative success from population decline.

Methylorubrum extorquens AM1 is a laboratory bacterial strain used to investigate methylotrophy, the use of reduced one-carbon compounds such as methanol. The ATCC collection identifies AM1 with deposit ATCC 14718 and designation NCIB 9133. It explicitly marks this as not the type strain. A widely used experimental strain and the reference that anchors a species name need not be the same culture.^[ref]

AM1 makes a metabolic hypothesis testable. In a 2005 study, an AM1-derived mutant lacking functional methanol dehydrogenase could not perform the usual first oxidation from methanol to formaldehyde. Researchers compared its colonization of Medicago truncatula with that of a fluorescently marked reference derivative. The mutant was disadvantaged in competition, yet separately inoculated mutants could reach populations comparable to the wild type. Methanol utilization therefore contributed to competitive success without being indispensable for colonization in that experiment.^[ref]

For a distinct illustrative calculation, suppose both populations start at $10^4$ cells, but finish at $4\times 10^4$ and $1.6\times 10^5$. Both grew, yet the first population's fraction fell from $1/2$ to $1/5$. A declining competitive fraction is thus compatible with an increasing absolute population. The reference, mutant, host and measured quantity all belong to the meaning of an AM1 experimental result.

A nomenclatural type anchors a taxon name to a reference. In prokaryotic nomenclature, it need not be the most typical member. For a species this is normally a type strain; for a genus it is a designated species.^[ref]

A reference and a statistical representative need not coincide. Suppose a hypothetical group contains bacterial strains T, U and V, with a stipulated trait measured as 1, 10 and 11 arbitrary units. Its arithmetic mean is $22/3\approx 7.33$ units. Designating T as the type strain does not require its measurement to be close to that mean. Conversely, choosing U because its value lies closer to the mean would not itself make U the designated reference.

The nomenclatural type also makes naming decisions interpretable when a taxon is divided or combined with another. It supplies an anchor for applying an existing name through a change of circumscription.^[ref]

The naming rules do not themselves delimit taxa or determine their biological relationships. Evidence about genomes and phenotypes supplies a different kind of information.^[ref]

Pasteurella multocida is a species of Gram-negative bacteria associated with animal hosts and diseases, including fowl cholera. Different bacterial strains can differ in host association and molecular properties; one sequenced isolate does not exhaust the diversity of the species.^[ref]

In 2001, investigators reported the genome of the avian isolate Pm70, predicting 2,014 coding sequences. Sequence comparisons identified candidate functions associated with virulence and iron acquisition. This supplied testable molecular leads, rather than direct proof that every predicted gene caused disease.^[ref]

An existing biochemical example makes the distinction between prediction and measurement concrete. Work on its hyaluronan synthase characterized use of two activated sugar substrates to build hyaluronic acid, whose chain alternates glucuronic acid and N-acetylglucosamine. An enzyme assay tests the actual chemical activity of a preparation; a sequence match proposes a possible activity that still needs such tests.^[ref]

The species name, bacterial strain, genome annotation and measured enzyme function therefore answer different biological questions. Keeping them distinct makes comparisons among isolates more informative than assigning every property of one isolate to all members.

A pathovar is an infrasubspecific grouping of bacterial strains distinguished by disease responses in one or more hosts. The criterion concerns pathogenic characteristics and bacterial host range, rather than simply the collection from which a strain came. The 2022 revision of the prokaryotic naming code lists pathovar in its advice on infrasubspecific subdivisions; Rule14a places designations below subspecies outside the code's principal Rules and Recommendations.^[ref]

The name Pseudomonas syringae pv. tomato DC3000 shows the levels of information. Pseudomonas syringae is the species designation, pv. tomato supplies the pathovar designation and DC3000 specifies the bacterial strain. The published DC3000 genome study describes disease on both tomato and Arabidopsis thaliana.^[ref] The word tomato in the name therefore does not mean that only tomato can be affected.

A bacterial host range observation is bounded by the hosts and conditions tested. If two strains share a species name but produce different responses across a host panel, the panel can reveal a pathogenic distinction. It does not by itself establish that the strains are genetically identical within each group, nor determine responses in every untested host. A pathovar designation summarizes a biological pattern while the individual strain record preserves which material was actually measured.

Prokaryotic nomenclature is the system of rules used to attach scientific names to taxa of bacteria and archaea. Naming supplies stable references for scientific communication; deciding which organisms belong together remains a question of taxonomy and evidence. The 2025 revision of the International Code of Nomenclature of Prokaryotes explicitly preserves freedom of taxonomic thought.^[ref]

A nomenclatural type anchors a name to a reference element. A type strain serves this role for a named species under the ordinary species rules. The reference need not be the most typical member of its group: it fixes how the name is applied when the boundaries of a taxon are reconsidered.^[ref]

For an invented classification example, suppose a named species contains bacterial strains A, B and C, with A its type strain. New evidence divides the group into A+B and C. Anchoring the old name to A identifies which resulting group retains that reference; finding that C has an unusual metabolism does not itself move the name to C. The example separates a reproducible naming decision from the biological evidence for splitting the group.

A species name combines a genus name with a specific epithet. Valid publication and the use of a correct name involve further rules, including publication and priority requirements. A name appearing somewhere in print is therefore not automatically a name with standing under this Code.^[ref]

Pseudomonas is a taxonomic genus of bacteria. Its type species is Pseudomonas aeruginosa, and it also contains Pseudomonas syringae. A type species anchors the genus name in biological nomenclature; it is not an assertion that every member has the same physiology or ecological role.^[ref]

The distinction matters in plant experiments. A study of Pseudomonas syringae can identify the particular bacterial strain used, its host and its measured effects, without turning those results into a universal property of Pseudomonas. In a 2011 Arabidopsis thaliana study, researchers measured both growth of the challenge strain and disease symptoms. Those are biological outcomes attached to a specified experimental system.^[ref]

For an identification example, Pseudomonas sp. records genus-level assignment while leaving the species unspecified. Replacing that label with Pseudomonas aeruginosa adds information requiring evidence. Conversely, pooling counts from several Pseudomonas species answers a genus-level abundance question while concealing their individual contributions.

Pseudomonas syringae is a species of bacteria in Pseudomonas, important in the study of interactions between plants and their associated microorganisms. Its nomenclatural type strain is deposited under identifiers including ATCC19310 and NCPPB281. Such collection identifiers locate reference material; they are not interchangeable with every experimental bacterial strain assigned to the species.^[ref]

A 2011 experiment used the strain reported as Pseudomonas syringae pv. tomato DC3000 to challenge Arabidopsis thaliana. Plants were grown with or without candidate bacterial colonists. Some Sphingomonas isolates reduced both pathogen growth and disease symptoms, whereas the tested Methylobacterium strains did not show that protective effect. The experiment asked whether prior colonization changed an observed disease outcome, rather than merely whether both organisms could be detected on a leaf.^[ref]

Pathogen population and host damage are distinct readouts. In an invented normalized-count example, $10^6$ versus $10^5$ colony-forming units per gram of leaf differs tenfold, or by one base-ten logarithmic unit. That calculation alone supplies neither a disease-severity score nor proof of a particular protective mechanism. Host, strain identity and measurement conditions remain part of the interpretation.

Pseudomonas syringae pv. tomato DC3000 is the name used for a well-studied bacterial strain in experimental interactions with tomato and Arabidopsis thaliana. The abbreviation pv. denotes pathovar, a classification related to pathogenic characteristics, while DC3000 identifies the particular strain. Those parts of the label carry more information than the species name Pseudomonas syringae alone.^[ref]

The 2003 genome report described about 6.5 megabases of DNA, comprising one circular chromosome and two plasmids, with 5763 predicted open reading frames. The assembly and annotation created a reference for comparing molecular observations, rather than merely attaching a name to a culture.^[ref] A predicted open reading frame is not automatically an experimentally established protein function.

In a 2011 plant-community experiment, this strain supplied a common challenge against which different bacterial colonists were compared. Both pathogen population and host disease symptoms were measured.^[ref] Holding the challenge strain fixed makes differences between colonist treatments easier to interpret. It does not make the experiment representative of every Pseudomonas syringae strain or every host.

Sphingomonas is a taxonomic genus of bacteria. Its type species is Sphingomonas paucimobilis; the genus name is validly published in the prokaryotic naming system. A bacterial strain, an individual species and the genus are different levels of identification.^[ref]

A2011 experiment made that distinction consequential. Researchers grew Arabidopsis thaliana with or without candidate bacterial colonists, then challenged the plants with the leaf pathogen Pseudomonas syringae. Many plant-derived Sphingomonas isolates reduced both disease symptoms and pathogen growth. Isolates obtained from air, dust or water did not necessarily protect, even at comparable bacterial densities on the plant.^[ref]

The experiment distinguishes colonization from a protective function. Finding a Sphingomonas sequence or a high bacterial count does not by itself show disease suppression. A controlled comparison needs the particular bacterial strain, host and outcome. Differences in carbon-source use suggested competition as one possible mechanism, but did not exclude other explanations.^[ref]

A type strain is a living reference lineage designated as the nomenclatural type of a species or subspecies in prokaryotic nomenclature. It consists of cultures descended from the designated strain, rather than one uniquely irreplaceable physical vial. The Code expects close agreement with the original description.^[ref]

This role supports comparisons between biological observations and a named reference. Culture collections preserve and identify such material; their accession identifiers can supply different labels for the same underlying type strain.^[ref]

Consider a constructed database example. Collection A labels the designated lineage A-101, while collection B labels a documented descendant B-202. Counting the two accessions as two independent species would confuse storage records with biological classification. The essential record is the documented relationship between the materials, the designated lineage and the name.

A type strain supplies a reference, not a guarantee that every other bacterial strain in the same species has identical phenotypes. It is also a living lineage whose measured properties require appropriate characterization. A comparison should state the actual material and conditions tested, so that a discrepancy can be investigated rather than silently attributed to an entire species.