Revision of the Nomenclature for the Bacillus thuringiensis Pesticidal Crystal Proteins

Abstract

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.

Bacteria used in the biological control of plant-parasitic nematodes: populations, mechanisms of action, and future prospects

“…Some Cry proteins are also toxic to other invertebrates such as nematodes, mites and protozoans (Feitelson et al, 1992). To date, there are six Cry proteins (Cry5, Cry6, Cry12, Cry13, Cry14, Cry21) known to be toxic to larvae of a number of free-living or parasitic nematodes (Alejandra et al, 1998;Crickmore et al, 1998;Marroquin et al, 2000;Wei et al, 2003;Kotze et al, 2005). On the basis of amino acid sequence homology, these nematode-affecting Cry proteins (except for Cry6A) were assigned to a single cluster in the main Cry lineage, parallel to other main groups (Bravo, 1997;Marroquin et al, 2000).…”

PCR-based identification of Bacillus thuringiensis pesticidal crystal genes

“…Even though the homology between two cry sequences within the same group can be as low as 45%, the homology of some speci¢c regions within the sequences can be as high as 95%. Because of this homology between cry gene sequences, the development of speci¢c probes was used earlier to detect and characterize putative new cry genes, using hybridization techniques [61]. With the advent of faster and more reliable technologies and, especially, with the increasing number of characterized cry genes, this methodology was abandoned due to its low speci¢city and the high number of probes required.…”

Why Bacillus thuringiensis insecticidal toxins are so effective: unique features of their mode of action

“…Most of the research has been done with toxins active on Lepidoptera, designated Cry1 (see [8] for the terminology). The structures of a Cry1 toxin, Cry1Aa, and of a toxin active on Coleoptera, Cry3A, have been determined and are very similar despite only about 25^30% amino acid sequence identity [9,10].…”