Distribution of cryI, cryII and cryV genes within Bacillus thuringiensis isolates from Spain

Using a PCR-based approach, a collection of 223 isolates of Bacillus thuringiensis from Spain was screened for the presence of cry genes belonging to three families. Genes from the cryI, cryII and cryV families were found in 54%, 42%, and 66% of the isolates, respectively. Only 23% of the isolates did not show the presence of any of the genes tested. Frequencies of these genes were compared in isolates from soil samples and from samples of cereal stores and mills, being this higher in the latter Specific primers were used to detect cryIA(a), cryIA(b), cryIA(c), cryIA(d), cryIA(e), cryIB, cryIC, cryID, cryIE, cryIF and cryIG genes. Within the cryI family, the most frequent gene was cryIA(c) (62%), followed by cryIA(a), cryID, cryIC and cryIA(b) (49, 43, 35, and 34%, respectively). A high frequency of joint occurrence was observed for cryIC and cryID; the latter was present in 93% of the isolates-containing cryIC. A random sample of 97 isolates was tested for toxicity against the insect pests Plutella xylostella and Spodoptera exigua. Among the isolates showing toxicity, the most common gene combination was cryIA-cryIC-cryID-cryII-cryV. Although in mo st cas es toxicity could be related to gene content, in some others toxicity was unexpected according to the results obtained by PCR. We found no apparent relationship between gene content in our isolates and the serovar to which they belong.