Enterobacterales is an order of Gram-negative, non-spore forming, facultatively anaerobic, rod-shaped bacteria with the class Gammaproteobacteria.[1] The type genus of this order is Enterobacter.
The name Enterobacterales is derived from the Latin term Enterobacter, referring the type genus of the order and the suffix "-ales", an ending used to denote an order. Together, Enterobacterales refers to an order whose nomenclatural type is the genus Enterobacter.
Enterobacterales was proposed in 2005 under the name "Enterobacteriales". However, the name "Enterobacteriales" was not validated according to the rules of the International Code of Nomenclature of Prokaryotes, thus it lacked standing in nomenclature, so the name was written in parentheses. "Enterobacteriales" was a monotypic order, containing only the family Enterobacteriaceae, and shared its type genus Escherichia.[2] [3] [4] The order contained a large, diverse group of species, occupying distinct ecological niches and possessing a variety of biochemical characteristics.[5] Many genera within the order have significant impacts on human activity, such as the pathogenic species Escherichia coli, Salmonella enterica, and Yersinia pestis, as well as agriculture-harming phytopathogens such as members of the genera Dickeya, Pectobacterium, Brenneria, Erwinia and Pantoea. The large number of species as well as the range of different biochemical characteristics made describing the order and its subgroups extremely difficult. The assignment and classification of this order was largely based on 16S rRNA genome sequences, which is known to have low discriminatory power and yield different results depending on the algorithm and organism strain used. In addition, these analyses have shown that 'Enterobacteriales' exhibited polyphyletic branching, with distinct subgroups.
In 2016, "Enterobacteriales" was proposed to be reclassified as Enterobacterales, and the type genus changed to Enterobacter in accordance with the International Code of Nomenclature of Prokaryotes. In addition, several new families within the order Enterobacterales were proposed, consisting of species that were formerly members of the family Enterobacteriaceae based on groupings found in phylogenetic trees constructed based on conserved genomes, 16S rRNA sequences and multi-locus sequence analysis as well as independent molecular markers (conserved signature indels).
As of 2021, the order Enterobacterales contains 7 validly published families (Budviciaceae, Enterobacteriaceae, Erwiniaceae, Hafniaceae, Morganellaceae, Pectobacteriaceae and Yersiniaceae).[6]
Analyses of genome sequences from Enterobacterales species identified five conserved signature indels (CSIs) for this order in the proteins peptide ABC transporter permease, elongation factor P-like protein YeiP, L-arabinose isomerase, pyrophosphatase, and a hypothetical protein, which in most cases are exclusively shared by either all or most members of this order. These CSIs provide a molecular means of demarcating this order from other Gammaproteobacteria and supports the monophyletic nature of the order Enterobacterales.
The following genera have been validly published, thus they have "Standing in Nomenclature". The year the genus was proposed is listed in parentheses after the genus name.