Host range and gene contents of Bacillus thuringiensis strains toxic towards Spodoptera exigua

Abstract

Thirty‐five strains of the entomopathogenic bacterium Bacillus thuringiensis active on Spodoptera exigua, were characterized by means of serological identification and determination of cry gene contents by PCR. The insecticidal activity of these 35 strains was further confirmed against S. exigua and tested against two other species of the same genus: S. littoralis and S. frugiperda. The results indicate that serovars aizawai, thuringiensis, and kurstaki were the most frequent within S. exigua ‐active strains and that serovar aizawai had the highest number of strains exhibiting toxicity against the three species bioassayed. The presence in cry genes as determined by PCR suggests a non random distribution of some cry genes among serovars. Genes cry1C, cry1D, and cry1E, which are known to code for proteins toxic against Spodoptera species, were very common within S. exigua‐active strains, specially in those belonging to serovar aizawai. However, some strains harbouring one or more of these genes were not toxic to S. littoralis or S. frugiperda; and some strains lacking all of the Spodoptera‐active genes were found to be toxic to all three species. This suggests differences in the expression levels among strains bearing toxic genes and the involvement of other genes toxic to Spodoptera species. Since strains sharing the same cry genes exhibited different host ranges, the results indicate the need to perform toxicity bioassays in addition to other tests (serological identification and PCR) in order to determine the insecticidal activity of B. thuringiensis strains.

Association analysis between serotype, cry gene content, and toxicity to Helicoverpa armigera larvae among Bacillus thuringiensis isolates native to Spain

“…However, the serovar-dependent distribution of plasmid-borne cry genes is more diYcult to explain, and may be related to some plasmid transfer speciWcity among strains of the same serovar (Baum and Gonzalez, 1992). In contrast, despite a lack of direct correlation between serovars and insecticidal activities, some serovars are known to contain high numbers of strains active against particular insect species (Dulmage, 1981;Porcar et al, 2000). Our results are in agreement with these observations, as this speciWcity may be related to the occurrence of certain speciWc genes, such as cry1C, which are more frequent in some serovars, such as aizawai (Porcar et al, 2000).…”

“…In contrast, despite a lack of direct correlation between serovars and insecticidal activities, some serovars are known to contain high numbers of strains active against particular insect species (Dulmage, 1981;Porcar et al, 2000). Our results are in agreement with these observations, as this speciWcity may be related to the occurrence of certain speciWc genes, such as cry1C, which are more frequent in some serovars, such as aizawai (Porcar et al, 2000). In other words, it seems that serovars will often contain strains that are toxic against insects susceptible to the frequently occurring toxins.…”

“…This system is still useful although the insecticidal activity rarely corresponds to the serotype. B. thuringiensis strains frequently produce crystalline inclusions containing more than one type of insecticidal protein and variation in toxicity between this inclusions has been recently reported between as well as within serovars (Porcar et al, 2000).…”

Molecular characterization of indigenous Bacillus thuringiensis strains isolated from Kashmir valley

“…All these five strains were found to have proteins of *135 and *65 kDa. Porcar et al (2000) reported that Cry1C, Cry1D, Cry1E, Cry1F and Cry9C proteins were highly toxic towards Spodoptera species. Earlier Tabashnik et al (1994) reported that Cry1Aa, Cry1Ab, Cry1Ac, Cry1B, Cry1C, Cry1F and Cry2A were highly toxic to P. xylostella.…”

Molecular characterization of local strains of Bacillus thuringiensis in the North of Algeria

“…The authors could not discriminate between the two species until after the observation by scanning electron microscope, which allowed the visualization of the parasporal crystal which is present only in B. thuringiensis and responsible for entomopathogenic activity of this bacterium against several devastating species. The toxicity of B. thuringiensis did not depend on Cry gene content only because factors other than Cry proteins may contribute to toxicity as well as spore interaction with crystal protein and the other soluble toxins such as β-exotoxin (Porcar et al, 2000). Martinez et al (2004) suggested that the biological activity of a strain cannot be fully predicted on the basis of its Cry gene content alone.…”