Insecticidal Proteins of Bacillus Thuringiensis and Their Application in Agriculture

Abstract

The insecticidal bacterium Bacillus thuringiensis (Bt) is the most commercially successful biological control agent of insect pests (Glare and O’Callaghan, 2000). Bt is a ubiquitous soil bacterium isolated from soil, stored grain, insect cadavers and the phylloplane (plant surface) (Martin and Travers, 1989). Thus, three prevailing niches of Bt can be envisaged viz., as an entomopathogen, as a phylloplane inhabitant and as a soil microorganism. Bt is a gram-positive, aerobic, endosporeforming bacterium belonging to morphological group I along with Bacillus cereus, Bacillus anthracis, and Bacillus laterosporus (Parry et al., 1983). All these bacteria have endospores. Bt, however, is recognized by its parasporal body (known as the crystal) that is proteinaceous in nature and possesses insecticidal properties. The parasporal body comprises of crystals varying in size, shape and morphology (Figure 1). Bt does not have a significant history of mammalian pathogenicity, and research has concentrated on the insecticidal nature of the crystal proteins, especially Sendotoxins. Considerable amount of information with respect to various aspects of Bt such as fermentation (Bryant, 1994), biology and genetics (Aronson et al., 1986), molecular biology (Hofte and Whiteley, 1989; Kumar et al., 1996; Schnepf et al., 1998), mechanism of action (Knowles, 1994), application as biopesticide (Federici, 1999), and Bt transgenic plants (Schuler et al., 1998; de Maagd et al., 1999) is available. The classification and nomenclature of Bt toxins has been recently described (Crickmore et al., 1998). To date, more than 100 different genes encoding crystal proteins have been cloned from Bt and two other species (Schnepf et al., 1998). Recent information about Bt proteins/genes can be obtained from http://www.biols.susx.ac.uk/Home/Neil-CrickmoreSt/.