Bacillus thuringiensis endotoxin production: a systematic review of the past 10 years

Bacillus thuringiensis (Bt) is one of the most promising biological control agents used commercially. Its products can contribute to reducing ecological and environmental problems associated with the use of chemical pesticides. Among the limiting factors of using Bt as bioinsecticide are the costs and ensuring its biological activity, which may vary according to the strain and culture conditions. This systematic review aimed to collect state-of-the-art information on the production of Bt endotoxins and to score the methodological feasibility of the data obtained, thus highlighting possible incoherencies. In order to consolidate recent findings and guide future studies, a total of 47 original articles from the last 10 years was analysed, with special attention being given to corroborating data, identifying inconsistencies and suggesting future adjustments so as to increase data reliability. With a maximum score of 8 points, three production parameters were classified on the following scale: preferable (score: 2), adequate (score: 1) and inadequate (score: 0), and another two parameter were classified as adequate (score: 1) or inadequate (score: 0). No article scored more than 6 out of the maximum of 8, thus reflecting the need for more detailed studies regarding Bt endotoxin production. The lack of standardization of methods and units of measurement also have made a comparison of results and an overall analysis difficult. Standards are suggested in the present study. The inclusion of bioassays and quantifying toxin via alkaline dilution are strongly recommended for studies of this nature, along with LC50 expressed in mg/L. Sixteen articles (34%) did not use either of these suggested methods, which indicates the need for further supporting studies. These findings reinforce the need for robust studies in this area, which could include the development of more affordable and effective bioinsecticides, thus increasing their competitiveness against insecticides derived from unsustainable sources.