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This article is about the bacterial class. For the genus, see Bacillus. For rod-shaped bacteria in general, see bacillus (shape).
Bacillus subtilis Gram.jpg
Bacillus subtilis, Gram stained
Scientific classification e
Domain: Bacteria
Phylum: Firmicutes
Class: Bacilli

Bacilli refers to a taxonomic class of bacteria. It includes two orders, Bacillales and Lactobacillales, which contain several well-known pathogens such as Bacillus anthracis (the cause of anthrax).


Several related concepts make use of similar words, and the ambiguity can create considerable confusion. The term "Bacillus" (capitalized and italicized) is also the name of a genus that, among many other genera, falls within the class Bacilli.

Also, "bacillus" (or the plural "bacilli") can be a generic term to describe the morphology of any rod-shaped bacterium. This general term does not mean that the subject is a member of class Bacilli or genus Bacillus. Thus, it does not necessarily imply a similar group of characteristics. Not all members of class Bacilli are rod-shaped (Staphylococcus is spherical), and many other rod-shaped bacteria that do not fall within that class (Clostridium kamina dalla kotta is rod-shaped but very different taxonomically) exist. Moreover, the general term "bacillus" does not necessarily indicate the Gram-positive staining common to class Bacilli. For example, E. coli is a rod-shaped bacterium that could, therefore, be described as "a bacillus", but it stains Gram-negative and does not belong to genus Bacillus or class Bacilli. Some microbiologists have forsaken the general "bacillus" term because of the confusion it can create.


The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature:[1] [2] and the phylogeny is based on 16S rRNA-based LTP release 106 by 'The All-Species Living Tree' Project [3]


Alicyclobacillaceae [incl. Bacillus tusciae & Tumebacillus permanentifrigoris]



Bacillus schlegelii

Thermicanus aegyptius {Bacillales Family X. Incertae Sedis}



Bacillus species group 14

Paenibacillaceae 1

Bacillaceae 4 [incl. Pullulanibacillus naganoensis, Sinobaca qinghaiensis & Tuberibacillus calidus]


Bacillus species group 13

Bacillus species group 12 [incl. Anaerobacillus]

Bacillus species group 11

Bacillus species group 10

Bacillus taeanensis

Bacillaceae 3

Bacillus species group 9

Bacillus species group 8

Bacilli part 2


Unclassified Bacillales

♠ Strains found at the National Center for Biotechnology Information (NCBI) but not listed in the List of Prokaryotic names with Standing in Nomenclature LPSN

Bacilli part 2 (continued)[edit]

Bacilli part 2

Bacillus species group 7

Bacillus species group 6

Bacillus species group 5 [incl. Aeribacillus pallidus]

Bacillus coagulans


Bacillus aeolius

Bacillaceae 2

Bacillus smithii

Bacillus badius

Exiguobacterium {Bacillales Family XII. Incertae Sedis}

Paenibacillaceae 2

Bacillus species group 4 [incl. Falsibacillus pallidus]

Bacillus species group 3


Bacillus species group 2

Bacillus species group 1


Planococcaceae [incl. Acetobacter pasteurianus ascendens, Lysinibacillus, Psychrobacillus, Viridibacillus & various Bacillus sp.]

Bacillus coahuilensis


Gemella {Bacillales Family XI. Incertae Sedis}


Turicibacter sanguinis

Haloplasma contractile

Erysipelotrichaceae [incl. Anaerorhabdus furcosa, Sharpea azabuensis, Streptococcus pleomorphus and various Clostridium, Eubacterium & Lactobacillus sp.]




  1. ^ See the List of Prokaryotic names with Standing in Nomenclature. Data extracted from J.P. Euzéby. "Bacilli". Retrieved 2012-05-17. 
  2. ^ See the NCBI webpage on Bacilli Data extracted from Sayers; et al. "NCBI Taxonomy Browser". National Center for Biotechnology Information. Retrieved 2012-05-17. 
  3. ^ See the 'The All-Species Living Tree' Project [1]. Data extracted from the "16S rRNA-based LTP release 106 (full tree)" (PDF). Silva Comprehensive Ribosomal RNA Database. Retrieved 2012-05-17.