IRREGULAR CRYSTAL-FORMATION IN SOME ISOLATES OF BACILLUS-THURINGIENSIS

A form of Bacillus thuringiensis was repeatedly isolated from African soil samples in which cells appear to differentiate into spore-forming and crystal-forming cells. Cells in which spores mature do not show a ny signs of crystal development, whereas other cells produce a large, composite, crystalline structure which is released during lysis and wh ich we interpret as being equivalent to the parasporal crystal of othe r strains of B. thuringiensis. The crystalline structure consists of a n irregular main body and an oblong appendage. In 2-day-old cultures t he ratio of free spores to free crystals is approximately 6, but subse quently drops to below 1. Bioassays with washed preparations of five i solates against 10 insect species showed that one isolate was weakly v irulent against larvae of Plutella xylostella. (C) 1994 Academic Press , Inc.