TITLE:
An Overview on the Crystal Toxins from Bacillus thuringiensis
AUTHORS:
Veloorvalappil N. Jisha, Robinson B. Smitha, Sailas Benjamin
KEYWORDS:
Bacillus thuringiensis; δ-Endotoxin; Resistanc
JOURNAL NAME:
Advances in Microbiology,
Vol.3 No.5,
September
11,
2013
ABSTRACT: Strains of Bacillus
thuringiensis (Bt) are
known to produce crystalline proteins (δ-endotoxins) concomitantly with
sporulation during their stationary phase of growth, which are demonstrated as lethal to
lepidopeterous, coleopeterous and dipterous insects in addition to mites,
nematodes, protozoa and flukes. Upon ingestion, the δ-nascent endotoxin
is an inactive protoxin complex of (Cry alone or Cry and Cyt toxins together) high molecular mass, which is cleaved upon
ingestion into the active component proteins at the high alkaline environments
in the digestive tract of these agricultural pests. Conventionally, Bt-crystals
are being produced employing submerged or liquid fermentation techniques in commercial
media, but recently many workers have used solid-state
fermentation strategy for the enhanced production of Bt-toxin at low
cost. Apart from δ-endotoxin, some isolates of Bt produce another
class of insecticidal small molecules called β-exotoxin (thuringiensin),
which may be harmful to humans. Moreover, resistance to Bt developed in various target
pest is yet another concern for Bt-industry.
Following a brief introduction, this review addresses various toxins produced
by various strains of Bt, Bt production media and media formulations with emphasis to solid-state fermentation,
general structure of Cry toxin, its mode of action, target pests, bioassay, resistance to Bt toxins and
resistance management. Briefly, this review would provide the readers an
overview on the general aspects of Bt toxin, its general structure and mechanism of action.