CHARACTERIZATION OF A NOVEL STRAIN OF BACILLUS-THURINGIENSIS

Bacillus thuringiensis is a well-known species of entomopathogenic bac teria that is widely used as a biopesticide against many insect pests. Insecticidal proteins, coded for by genes located in plasmids, form t ypical parasporal, crystalline inclusions during sporulation. In this report, an unusual strain of B. thuringiensis subserovar oyamensis (LB IT-113), isolated from living larvae of Anopheles pseudopunctipennis i n Mexico, was characterized by its ultrastructure, the protein composi tion of its parasporal crystal, plasmid pattern, and toxicological pro perties against several insect and noninsect targets. The parasporal c rystal is enclosed within the spore's outermost envelope (exosporium), as determined by transmission electron microscopy, and exhibits a squ are, flat shape. Its main components are two proteins with sizes of 88 and 54 kDa. Despite some crystal morphology resemblance, both protein s are immunologically unrelated to the Cry IIIA protein, as shown by i mmunoblot analysis, when probed with antisera raised against the 88-kD a protein and the Cry IIIA protein. Partial N-terminal sequence of the 88-kDa protein revealed a unique amino acid arrangement among the Cry proteins. Solubilization of the crystal proteins was achieved at 3.3 M NaBr, and its digestion with trypsin showed only one ca; 60-kDa pept ide, as observed by sodium dodecyl sulfate-polyacrylamide gel electrop horesis. The patterns of three plasmids of strain LBIT-113 were consid erably different from those of B. thuringiensis subspp. kurstaki, tene brionis, and israelensis. Parasporal crystals showed no toxicity to la rvae of four species of caterpillar, three species of mosquito, two sp ecies of beetle, one species of cricket, one species of ant, one speci es of aphid, one species of nematode, one species of ostracod, one spe cies of ameba, and one species of rotifer.