Bacillus thuringiensis Toxin Nomenclature:

Bacillus thuringiensis Toxin Nomenclature:
The Bacillus thuringiensis delta-endotoxin nomenclature committee was set up in 1993 in order to update the nomenclature originally devised in 1989 by Hofte and Whiteley (Microbiological Reviews 53:242-255) and consists of the following committee members.

The current nomenclature, based solely on amino acid identity, allows closely related toxins to be ranked together and removes the necessity for researchers to bioassay each new toxin against a growing series of organisms. Biological specificity being a component of the orginal nomenclature. Roman numerals have also been exchanged for Arabic numerals in the primary rank (eg CryIIIA became Cry3A). Each new toxin is assigned a unique name incorporating four ranks. A completely new toxin might therefore be assigned the name Cry50Aa1. For the sake of convenience we propose that the use of the quaternary rank (which distinguishes between toxins that are more than 95% identical) is optional, only being used for the sake of clarity. Note that quaternary ranks are assigned to each independently sequenced toxin gene, thus despite the fact that some toxins have different quaternary ranks - they may in fact be identical.

Vip Nomenclature:
A nomenclature for the Vip and Vip-related toxins can be found here

Parasporin Nomenclature:
A new nomenclature for the sub-class of Bt toxins known as parasporins can be found here


Criteria for Inclusion:
The primary criterion for a toxin to be included in the nomenclature it must:

"have significant sequence similarity to one or more toxins within the nomenclature or be a Bacillus thuringiensis parasporal inclusion protein that exhibits pesticide activity or some experimentally verifiable toxic effect to a target organism"

Due to the large amount of data that are being generated as a result of genomic sequencing projects we are now having to be more strict when deciding whether or not to include a toxin in the nomenclature. Unless a toxin shares >95% sequence identity with an existing sequence then additional evidence will be required that that the sequenced gene encodes a toxin.

Binary Toxins:
An exception to the above applies to the recently described series of binary toxins. Crystal proteins can now be included in the nomenclature if together they exhibit a significant toxic effect whereas individually they do not.

Presentation of the Nomenclature:
There are a number of lists and figures available on this web site, clicking on the following links will open them in separate windows:

Full toxin list This lists all toxins within the nomenclature and the relationships between the binary toxin componants
Holotype list This simply lists the holotype toxin for each unique class
Three domain dendrogram This figure shows a dendrogram describing the relatedness of all the toxins believed to share the common three-domain structure
Other toxin dendrogram This figure shows a dendrogram describing the relatedness of the rest of the toxins within the nomenclature and includes related proteins not in the Bt nomenclature
Recent news Is updated whenever a new toxin is added to the nomenclature

Publication and Citation:
The following review was published in 1998:

Revision of the Nomenclature for the Bacillus thuringiensis Pesticidal Crystal Proteins
N. Crickmore, D.R. Zeigler, J. Feitelson, E. Schnepf, J. Van Rie, D. Lereclus, J. Baum, and D.H. Dean. Microbiology and Molecular Biology Reviews (1998) Vol 62: 807-813
It is also available online

Due to the fact that the nomenclature is constantly being updating we also recommend citing this Web Site. The correct format for doing this is:

Crickmore, N., Baum, J., Bravo, A., Lereclus, D., Narva, K., Sampson, K., Schnepf, E., Sun, M. and Zeigler, D.R. "Bacillus thuringiensis toxin nomenclature" (2018)

Aquiring a Name for Your Toxin:
Workers with a newly sequenced toxin are encouraged to submit it to the committee in order that a logical name be assigned to it. Before a toxin can be entered into the nomenclature it's sequence must be made publically available, usually via the EMBL or GenBank databases. We envisage that just prior to publication, or submission to a database, workers will submit their sequence to either Neil Crickmore or Dan Zeigler who will then consult the committee and assign a name to the toxin. This name can then be used in the publication / database submission. Alternatively sequences can be submitted elctronically using this form. We request that both DNA and protein sequences are submitted as this can greatly assist the naming process.

Bt toxin scanner
An online server is available for researchers to scan genomic sequences for Bt toxins and can be found at See Ye et al 2012 for more information.


Bt toxin specificity database
A relational database giving known insecticidal activities of the delta-endotoxins was set up by
Kees Van Frankenhuyzen and Carl Nystrom at but unfortunately is now no longer available