Bm. Hansen et al., MOLECULAR AND PHENOTYPIC CHARACTERIZATION OF BACILLUS-THURINGIENSIS ISOLATED FROM LEAVES AND INSECTS, Journal of invertebrate pathology, 71(2), 1998, pp. 106-114
Bacillus thuringiensis isolates from the phylloplane of organically cu
ltivated cabbage were characterized using molecular and phenotypic met
hods. Of the 58 isolates under study, 31 belonged to serovar kurstaki,
16 did not react with any of the currently recognized antisera, 7 rea
cted with known antisera, and 4 could not be serotyped as they were no
nmotile. Round crystals were found in 26 isolates, while bipyramidal c
rystals mere found in the remaining 32 isolates, all of which had acti
vity to lepidopteran larvae. Further, one isolate with unknown serotyp
e and round crystals had lepidopteran activity. Colony hybridization w
as found to be a useful tool for screening the isolates for specific g
ene homologies and showed good correlation with the phenotypic observa
tions. Polymerase chain reaction (PCR) was used for confirmation of th
e colony hybridization data, in most cases with concordant results. Ho
wever, in one case some of the colony hybridization data could not be
confirmed by PCR, due to DNA sequence variations in the binding area o
f one of the primers. The random amplified polymorphic DNA (RAPD) anal
ysis showed that isolates otherwise indistinguishable could be disting
uished by this method. However, the method was not able to distinguish
the 31 kurstaki isolates. Further, the kurstaki isolates could not be
distinguished from the B. thuringiensis serovar kurstaki HD-1 strain
used in commercial products for lepidopteran control. One of the isola
tes was a serovar israelensis, but no genes encoding dipteran activity
could be detected, and the RAPD analysis revealed that the DNA finger
print of this israelensis isolate deviated from the israelensis ONR60A
isolate used in commercial products. In conclusion we find that a mol
ecular method like colony hybridization is suitable for screening larg
e collections of bacteria. When colony hybridization data are combined
with RAPD analyses isolates can be grouped based on genetic potential
and DNA fingerprint, whereby further characterizations by PCR and the
more labourious phenotypic methods can be performed more effectively.
(C) 1998 Academic Press.