Peribacillus

''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.''

Members of ''Peribacillus'' were originally part of the genus ''Bacillus'', a large, phylogenetically complicated genus with unclear evolutionary relationships. The polyphyletic nature of the genus could be partially attributed to the vague criteria used to classify new species into this genus. To clarify the taxonomic relationships of ''Bacillus'', multiple phylogenetic and comparative genomic analyses have been conducted, resulting in the transfer of many ''Bacillus'' species into novel genera such as ''Virgibacillus, Solibacillus, Brevibacillus'' and ''Ectobacillus''. In addition, the genus was restricted to only include species closely related to ''Bacillus subtilis'' and ''Bacillus cereus''.

The name ''Peribacillus'' is derived from its placement in phylogenetic trees. The prefix "peri-" comes from the Greek preposition ''peri'', and translates to "about, around or nearby". ''Bacillus'' comes from the Latin noun ''bacillus'', referring to both 'a small staff or rod' and ''Bacillus'', the bacterial genus. Put together, the name ''Peribacillus'' refers to a genus around or nearby ''Bacillus''.

Biochemical characteristics and molecular signatures

Members of the genus ''Peribacillus'' are either aerobic or facultatively anaerobic and demonstrate endospore formation under adverse environmental or nutritional conditions. Most species have been isolated from either soil or human/animal guts. ''Peribacillus'' are usually motile, except in some cases when cells form and grow in chains. ''Peribacillus'' can survive in temperatures ranging from 3 °C to 45 °C, but optimal growth occurs in the range of 25-37 °C. ''Peribacillus butanolivorans'' is used in industrial processes, specifically in the remediation of butanol.

Genomic analyses have identified three conserved signature indels (CSIs) in the proteins HAMP domain-containing protein, phospho-N-acetylmuramoyl-pentapeptide-transferase and stage II sporulation protein E, which are specific for members of the genus ''Peribacillus'' and provide molecular means to distinguish members of this genus from other ''Bacillaceae'' genera and bacteria.

Taxonomy

As of May 2021, there are a total of 17 species with validly published names in the genus ''Peribacillus''. Members of this genus group together and forms a monophyletic branch in phylogenetic trees created from concatenated sequences from conserved proteins, 16S rRNA gene sequences as well as the phylogenetic tree in the Genome Taxonomy Database (GTDB).

Additional phylogenetic studies have identified a number of non-validly published species ("Bacillus cihuensis", "Bacillus massiliglaciei", "Bacillus massilioanorexius", "Bacillus massiliogorillae" and "Bacillus testis''")'' that are considered to be members of this genus as they branch with other members of ''Peribacillus'' in phylogenetic trees and share the same unique molecular markers (specifically conserved signature indels). However, transfer of these species into ''Peribacillus'' was not proposed due to the lack of strain culture information demonstrating the need for future analyses of this clade as more information become available.

References

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Bacteria genera
Bacillaceae