| Hypothetical example | ||||||||||||||||||
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| B is phylogenetically part of the A group but not taxonomically, so A is paraphyletic. |
In bacteriology, a taxon in disguise is a species, genus or higher unit of biological classification whose evolutionary history reveals has evolved from another unit of a similar or lower rank, making the parent unit paraphyletic. [1] [2] That happens when rapid evolution makes a new species appear so radically different from the ancestral group that it is not (initially) recognised as belonging to the parent phylogenetic group, which is left as an evolutionary grade.
While the term is from bacteriology, parallel examples are found throughout the tree of life. For example, four-footed animals have evolved from piscine ancestors but since they are not generally considered fish, they can be said to be "fish in disguise".
In many cases, the paraphyly can be resolved by reclassifying the taxon in question under the parent group. However, in bacteriology, since renaming groups may have serious consequences since by causing confusion over the identity of pathogens, it is generally avoided for some groups.
The bacterial genus Shigella is the cause of bacillary dysentery, a potentially-severe infection that kills over a million people every year. [3] The genus ( S. dysenteriae , S. flexneri , S. boydii , S. sonnei ) have evolved from the common intestinal bacterium Escherichia coli , which renders that species paraphyletic. E. coli itself can also cause serious dysentery, [4] but differences in genetic makeup between E. coli and Shigella cause different medical conditions and symptoms. [2]
Escherichia coli is a badly-classified species since some strains share only 20% of their genome. It is so diverse that it should be given a higher taxonomic ranking. However, medical conditions associated with E. coli itself and Shigella make the current classification not to be changed to avoid confusion in medical context. Shigella will thus remain "E. coli in disguise".
Similarly, the Bacillus species of the B. cereus-group ( B. anthracis , B. cereus , B . thuringiensis , B. mycoides , B. pseudomycoides , B. weihenstephanensis and B. medusa ) have 99-100% similar 16S rRNA sequence (97% is a commonly-cited adequate species limit) and should be considered a single species. [5] Some members of the group appear to have arisen from other Bacillus strains by acquiring a protein coding plasmid and so the group may thus be polyphyletic. For medical reasons, such as anthrax, the current arrangement of separate species has remained intact. [5]
Bacillus 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 is the name of the class of bacteria to which this genus belongs. Bacillus species can be either obligate aerobes which are dependent on oxygen, or facultative anaerobes which can survive in the absence of oxygen. Cultured Bacillus species test positive for the enzyme catalase if oxygen has been used or is present.
Shigella is a genus of bacteria that is Gram negative, facultatively anaerobic, non–spore-forming, nonmotile, rod shaped, and is genetically nested within Escherichia. The genus is named after Kiyoshi Shiga, who discovered it in 1897.
Swarming motility is a rapid and coordinated translocation of a bacterial population across solid or semi-solid surfaces, and is an example of bacterial multicellularity and swarm behaviour. Swarming motility was first reported by Jorgen Henrichsen and has been mostly studied in genus Serratia, Salmonella, Aeromonas, Bacillus, Yersinia, Pseudomonas, Proteus, Vibrio and Escherichia.
Bacterial taxonomy is subfield of taxonomy devoted to the classification of bacteria specimens into taxonomic ranks. Archaeal taxonomy are governed by the same rules.
Alkalihalobacillus is a genus of gram-positive or gram-variable rod-shaped bacteria in the family Bacillaceae from the order Bacillales. The type species of this genus is Alkalihalobacillus alcalophilus.
Neobacillus is a genus of rod-shaped bacteria that show Gram-positive or Gram-variable staining. This genus belongs under the family Bacillaceae within the order Bacillales. The type species of Neobacillus is Neobacillus niacini.
Cytobacillus is a genus of rod-shaped bacteria that stain either Gram-positive or Gram-variable in the family Bacillaceae within the order Bacillales. The type species for this genus is Cytobacillus firmus.
Peribacillus is a genus of rod-shaped bacteria that exhibits Gram-positive or Gram-variable staining that belongs in the family Bacillaceae within the order Bacillales. The type species for this genus is Peribacillus simplex.
Mesobacillus is a genus of gram-positive or gram-variable, rod-shaped bacteria in the family Bacillaceae within the order Bacillales. The type species for this genus is Mesobacillus jeotgali.
Ectobacillus is a genus of Gram-positive, rod-shaped bacteria in the family Bacillaceae within the order Bacillales. The type species for this genus is Ectobacillus panaciterrae.
Evansella is a genus of Gram-positive rod-shaped bacteria in the family Bacillaceae within the order Bacillales. The type species for this genus is Evansella cellulosilytica.
Ferdinandcohnia is a genus of rod-shaped bacteria that generally display Gram-positive staining in the family Bacillaceae within the order Bacillales. The type species for this genus is Ferdinandcohnia humi.
Gottfriedia is a genus of gram-positive or Gram-variable rod-shaped bacteria in the family Bacillaceae within the order Bacillales. The type species for this genus is Gottfriedia luciferensis.
Heyndrickxia is a genus of gram-positive rod-shaped bacteria in the family Bacillaceae within the order Bacillales. The type species for this genus is Heyndrickxia oleronia.
Lederbergia is a genus of gram-positive or Gram-variable, rod-shaped bacteria in the family Bacillaceae within the order Bacillales. The type species for this genus is Lederbergia galactosidilyticus.
Niallia is a genus of Gram-Positive rod-shaped bacteria in the family Bacillaceae from the order Bacillales. The type species of this genus is Niallia circulans.
Robertmurraya is a genus of mostly Gram-Positive rod-shaped bacteria in the family Bacillaceae from the order Bacillales. The type species of this genus is Robertmurraya siralis.
Schinkia is a genus of Gram-positive rod-shaped bacteria in the family Bacillaceae from the order Bacillales. The type species of this genus is Schinkia azotoformans.
Siminovitchia is a genus of Gram-Positive or Gram-negative rod-shaped bacteria in the family Bacillaceae from the order Bacillales. The type species of this genus is Siminovitchia fortii.
Weizmannia is a genus of Gram-Positive rod-shaped bacteria in the family Bacillaceae from the order Bacillales. The type species of this genus is Weizmannia coagulans.
