In this study, Bt-S84-13a, a native B. thuringiensis isolate from Penang Hill, Malaysia that has been previously reported to produce exosporium-enclosed parasporal inclusion, in addition to free parasporal inclusion, was characterized using a series of morphological, biochemical and molecular analysis. In terms of colony morphology, Bt-S84-13a showed 2.0-2.5 mm white colonies with a typical fried-egg appearance, glossy surface, slightly raised and entire margin. SDS-PAGE of crude protein extracted from sporulated cells of Bt-S84-13a showed four major bands at 46, 31, 28 and 26 kDa. However, the spore-crystal suspension of Bt-S84-13a was not pathogenic to the third instar larvae of Aedes aegypti, Aedes albopictus and Culex quinquefasciatus, although Bt-S84-13a was characterized with cry4 gene through PCR analysis. No correlation was found between the protein profile and cry gene pattern of Bt-S84-13a. Plasmid profiling showed that Bt-S84-13a contains only megaplasmid. Despite the effort of characterizing this unique Malaysian isolate, the actual ecological role of this unique strain remains puzzle and unclear. Further experiments should be performed to unveil the hidden potential in this native Malaysian B. thuringiensis isolate.
Key words: Bacillus thuringiensis, bioassay, cry gene, cyt gene, parasporal inclusion
|
