Industrial Production of Bacillus Thuringiensis Based Bio-Insecticide: Which Way Forward?

Considering long term negative effect of chemical insecticides on the environment and human health, globally biological pest management has been promoted. Bacillus thuringiensis (Bt) is mostly explored and commercially successful microbial insecticide. According to a report, it constitutes almost 2% of insecticide market [1]. There are at least 32 companies involved in Bt based bio-insecticide business [2]. Microbiologically, Bt is gram-positive, facultative anaerobic bacterium most common habitats of which are soil, water or plant surfaces [3]. It can produce almost nine distinct types of toxins, among them δendotoxin, which is toxic to a range of insects, is mostly studied for insecticidal application [3]. This type of toxin is also known as Cry protein or Cry toxin and belongs to a family of toxin called pore forming toxins. They can kill the larvae of different insect groups usually by forming pore in mid-gut cell membrane followed by celllysis [1]. There are at least 500 known cry gene sequences which are broadly divided into 67 groups named as Cry1 to Cry67 [1]. Expression of the genes encoding Cry toxin are controlled by certain RNA polymerase which is produced during sporulation. Cry toxin production, therefore, coincides with spore formation [2], and hence, achieving high spore count is one of the major targets of Bt fermentation.