''Xanthomonas citri'' is a

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 ...

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 Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...

. Although it is harmless for humans, it is a

phytopathogen Plant diseases are diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organ ...

, known for being the causing agent of

citrus canker Citrus canker is a disease affecting ''Citrus'' species caused by the bacterium '' Xanthomonas citri''. Infection causes lesions on the leaves, stems, and fruit of citrus trees, including lime, oranges, and grapefruit. While not harmful to huma ...

. Many

pathovar A pathovar is a bacterial strain or set of strains with the same or similar characteristics, that is differentiated at infrasubspecific level from other strains of the same species or subspecies on the basis of distinctive pathogenicity to one o ...

s are misclassified as ''X. cissicola'', '' X. campestris'', or '' X. axonopodis''. A 2022 study proposes moving 20 pathovars in these three (including the sole representative of ''X. cissicola'') into ''X. citri''. However, based on the principle of priority, all "''X. citri''" should become instead named under the earliest-published name, ''X. cissicola'' like in

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 ...

. The two proposals do not affect the independence of ''X. campestris'' and ''X. axonopodis'', as their type strains are sufficiently distinct from ''X. citri/cissicola'' to be their own species.

Pathovars included

Uncited entries are based on Bansal et al. (2022), either in the article's own results (20 pathovars) or in its description of earlier results. Pathovars that include the type strain of either ''X. citri'' or ''X. cissicola'' are shown in bold. The list is unlikely to be complete.

Bacterial killing via a secretion system

''Xanthomonas citri'' uses its type IV secretion system to kill other Gram-negative bacterial species in a contact-dependent manner. The secretion of the effector proteins requires a conserved C-terminal domain, and its

bacteriolytic Lysis ( ; from Greek 'loosening') is the breaking down of the membrane of a cell, often by viral, enzymic, or osmotic (that is, "lytic" ) mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a ' ...

activity is neutralized by a cognate immunity protein.

Defense against predators

''Xanthomonas citri'' also uses

type VI secretion system The type VI secretion system (T6SS) is one of the bacterial secretion systems, membrane protein complexes, used by a wide range of gram-negative bacteria to transport effectors. Effectors are moved from the interior of a bacterial cell, across t ...

in defense against the predatory amoeba ''

Dictyostelium discoideum ''Dictyostelium discoideum'' is a species of soil-dwelling Amoeboid, amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly referred to as slime mold, ''D. discoideum'' is a eukaryote that transitions from a collection of unic ...

''.

References

citri Bacterial citrus diseases Bacteria described in 1989 {{gammaproteobacteria-stub