Morphology of a spectrum of parasporal endotoxin crystals from cultures ofBacillus thuringiensis ssp kurstaki isolate A3-4

Morphology of the parasporal delta -endotoxin crystals of Bacillus thuringi ensis subsp. kurstaki isolate A3-4, a native (Taiwan) strain was studied by scanning (SEM) and transmission (TEM) electron microscopy. The typical bip yramidal crystals and an unusual parasporal inclusion with an embedded body were observed. The parasporal delta -endotoxin crystal with an embedded bo dy, which was in different size and shape was well demonstrated in thin sec tions by transmission electron microscopy. The sporulated cells had multipl e individually separated inclusions up to four crystals in one cell, which was unique to this isolate, and has not been reported before. The delta -en dotoxin crystals included in the cell or released from the cell after batch fermentation or fed-batch fermentation did not show any altered morphologi cal characteristics. However, judging from thin-sections of TEM, cells and the included parasporal crystals from fed-batch fermentation appeared large r than those from batch fermentation. It was observed that release of spore and parasporal crystals from the bacterial cell produced from batch cultur es was earlier than that of fed-batch cultures. Preliminary bioassay result s showed that the isolate cultures from both types of culture were equally effective against Plutella xylostella larvae. Based on the morphological ob servations, this strain may have a multiple insecticidal activities toward different insect species.