Effects of Bacillus thurungiensis Cry1A(c) δ-endotoxin on diversity of Legume Nodulating Bacteria (LNB) and nitrogen fixation in Clay soil

Abstract

Bt technology alleviates many problems associated with the use of chemical pesticides, contributes to increased grain yields and a reduced need for insecticidal sprays. However, the potential impacts of Bt crops on the environment remain a topic of debate worldwide, calling for the assessment of Bt crops on the environment. In the current study, the effect of Bacilllus  thuringiensis (Bt) Cry1A(c) d-endotoxin on the diversity of legume nodulating bacteria (LNB) and nitrogen fixation in clay soil was evaluated. Bt Cry1A(c) d-endotoxin from a  local B. thuringiensis isolate (ICIPE L1-2) active against Chilo partellus (Swinhoe) was used.  Beans  (Phaseolus  vulgaris  L.)  and  Siratro  (Macroptilium  atropurpureum DC.)  seedlings were  grown  in  pots  treated with Bt Cry1A(c)  d-endotoxin  solution  (100  μg/ml). Control  experiments were  treated with water. The  plants were maintained  in  the greenhouse until nodulation  (8 weeks)  stage when  sampling was done. LNB were  isolated  from  the  root  nodules. Restriction fragment  length polymorphism  (RFLP) assessed  the diversity of  the LNB  species. Soil  samples  in hungate  tubes were  treated with Bt Cry1A(c)  d-endotoxin  solution  (100  μg/ml)  and  the  control  sample  sprayed with  equally  volume  of  distilled water. Subsequently,  acetylene  reduction  assays  were  performed  over  a  60  hour  period.  The  results  showed  that  Bt  Cry1A(c)  d-endotoxin had no effect on nitrogen  fixation  rates by  free  living  soil microorganisms. However, RFLP data  showed a  slightly higher  diversity  of  LNB  in  the  control  samples  than  the  test  samples,  indicating  that  Bt  Cry1A(c)  d-endotoxin  (100  μg/ml) reduced or modified the number of LNB in the rhizosphere.

Key words: Bacillus thuringiensis, Bt Cry1A(c) δ-endotoxin, Macroptilium atropurpureum (DC.), RFLP.