Sporulation, Structure Assembly, and Germination in the Soil Bacterium Bacillus thuringiensis: Survival and Success in the Environment and the Insect Host

Abstract

Bacillus thuringiensis (Bt) is a rod-shaped, Gram-positive soil bacterium that belongs to the phylum Firmicutes and the genus Bacillus. It is a spore-forming bacterium. During sporulation, it produces a wide range of crystalline proteins that are toxic to different orders of insects. Sporulation, structure assembly, and germination are essential stages in the cell cycle of B. thuringiensis. The majority of studies on these issues have focused on the model organism Bacillus subtilis, followed by Bacillus cereus and Bacillus anthracis. The machinery for sporulation and germination extrapolated to B. thuringiensis. However, in the light of recent findings concerning the role of the sporulation proteins (SPoVS), the germination receptors (Gr), and the cortical enzymes in Bt, the theory strengthened that conservation in sporulation, structure assembly, and germination programs drive the survival and success of B. thuringiensis in the environment and the insect host. In the present minireview, the latter pinpointed and reviewed.

Multiple cry Genes in Bacillus thuringiensis Strain BTG Suggest a Broad-Spectrum Insecticidal Activity

“…When ingested by the insect or its larvae, the crystal protoxins are activated by proteases in the digestive system. The active toxins bind to specific receptors on the cells of the midgut, disrupt the membrane transport, and cause the death of the insect or its larvae after 2 to 48 h [ 8 , 9 , 10 , 11 , 12 ]. Currently, two molecular models describe Cry toxins’ insecticidal mechanisms of action: the sequential binding model, which suggests the formation of cell membrane pores, and the signaling pathway model describing a signaling cascade of cell apoptosis induction [ 13 ].…”