The mosquitocidal crystals of Bacillus thuringiensis subsp. fukuokaensis were isolated and bioassayed against fourth-instar larvae of two mosquito species. The 50% lethal concentration values of the crystals to Aedes aegypti and Cukx quinquefasciatus were 4.1 and 2.9 ,ug/ml, respectively. In addition, the solubilized crystals had hemolytic activity; 50 ,ug/ml was the lowest detectable level. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that the crystals consisted of polypeptides of 90, 86, 82, 72, 50, 48, 37, and 27 kDa. When the solubilized inclusion was treated with C. quinquefasciatus midgut brush border membrane vesicles or Manduca sexta gut juice, only one major protein was detected. This protein retained mosquitocidal activity but had no detectable hemolytic activity. Immunological analysis of this subspecies and the subspecies israelensis, kyushuensis and darmstadiensis by using polyclonal antisera raised against the whole-crystal protein of B. thuringiensis subsp. fukuokaensis revealed that the proteins in subsp. fukuokaensis are distinct from proteins in the other subspecies because little cross-reaction was observed. Analysis of the plasmid pattern showed that the crystal protein genes are located on a plasmid of 130 MDa. Analysis of plasmid and chromosomal DNA from subsp. fukuokaensis showed little homology to the 72-kDa toxin gene (PG-14) of B. thuringiensis subsp. morisoni. However, some of the proteins of B. thuringiensis subsp. fukuokaensis are homologous to other B. thuringiensis toxins because N-terminal amino acid analysis revealed that the 90-kDa protein is encoded by a crylV gene type. * Corresponding author. kyushuensis and subsp. morrisoni PG-14 share significant homology to the crystal toxin gene of subsp. israelensis (31). More recently the monoclonal antibodies directed against the 68-and 135-kDa toxins of subsp. israelensis have been shown to cross-react with the 26-and 75or 80-kDa proteins of subsp. kyushuensis, respectively (15). In this article we describe the characterization of crystals produced from B. thuringiensis subsp. fukuokaensis which are toxic to larvae of mosquitoes and which in solubilized form are hemolytic. Further, by means of polyclonal antisera specific for crystal proteins of this strain we show that the crystal proteins of this strain do not cross-react with those of three other mosquitocidal strains. Further, we have determined that a large plasmid encodes for the crystal proteins of subsp. fukuokaensis. MATERIALS AND METHODS Bacterial strains and culture conditions. The type strains of B. thuringiensis subsp. israelensis, fukuokaensis, kyushensis, and darmstadiensis (strain 73-E10-2) were from Kyushu University, Fukuoka, Japan. Two Crymutants used in this study, subsp. israelensis YG-1 and subsp. fukuokaensis YG-101, were prepared by curing the type strains as previously described (14). Growth of these strains was as described for B. thuringiensis subsp. israelensis (10). Purification and solubilization of crystals. The spore-crysta...