SUMMARY: During the past decade the pesticidal bacterium Bacillus thuringiensis has been the subject of intensive research. These efforts have yielded considerable data about the complex relationships between the structure, mechanism of action, and genetics of the organism’s pesticidal crystal proteins, and a coherent picture of these relationships is beginning to emerge. Other studies have focused on the ecological role of the B. thuringiensis crystal proteins, their performance in agricultural and other natural settings, and the evolution of resistance mechanisms in target pests. Armed with this knowledge base and with the tools of modern biotechnology, researchers are now reporting promising results in engineering more-useful toxins and formulations, in creating transgenic plants that express pesticidal activity, and in constructing integrated management strategies to insure that these products are utilized with maximum efficiency and benefit.

SUMMARY: The crystal proteins of Bacillus thuringiensis have been extensively studied because of their pesticidal properties and their high natural levels of production. The increasingly rapid characterization of new crystal protein genes, triggered by an effort to discover proteins with new pesticidal properties, has resulted in a variety of sequences and activities that no longer fit the original nomenclature system proposed in 1989. Bacillus thuringiensis pesticidal crystal protein (Cry and Cyt) nomenclature was initially based on insecticidal activity for the primary ranking criterion. Many exceptions to this systematic arrangement have become apparent, however, making the nomenclature system inconsistent. Additionally, the original nomenclature, with four activity-based primary ranks for 13 genes, did not anticipate the current 73 holotype sequences that form many more than the original four subgroups. A new nomenclature, based on hierarchical clustering using amino acid sequence identity, is proposed. Roman numerals have been exchanged for Arabic numerals in the primary rank (e.g., Cry1Aa) to better accommodate the large number of expected new sequences. In this proposal, 133 crystal proteins comprising 24 primary ranks are systematically arranged.

In 1998 a nomenclature for the growing list of pesticidal proteins from Bacillus thuringiensis (Bt) was derived based solely on protein sequence comparisons. This nomenclature was widely adopted and provided a robust framework for the naming and classification of the proteins. The success of these proteins in integrated pest management schemes prompted an increased effort to find others with improved or more diverse activities. These discovery activities led to the characterization of proteins from a wider range of bacteria and with a variety of different protein folds. Since most of these new proteins were grouped together as Cry proteins it became apparent that the existing nomenclature had limitations in representing the diverse range of proteins that had been identified. This revised nomenclature retains the basic principles of the 1998 version but provides specific mnemonics to represent different structural groups. For the purposes of consistency, the vast majority of the proteins have either retained their name or have a new name that clearly references the previous one. Other pesticidal proteins not previously included in the nomenclature have been incorporated into this version.