Bt Research, 2015, Vol.6, No.8, 1-15
6
conformed to the phylogenetic relatedness, their
RAPD genotypes were variable e. g. 5 genotypes (1, 5,
6, 11 and 12) were visible among the strains of
sub-cluster A1 which were from the biotype kurstaki.
This genetic diversity might be due to the presence of
many different plasmids in each strain and high
frequency of DNA rearrangements in variable regions
by conjugation transfer mechanism and the transposon-like
inverted repeats flanking the endotoxin genes. Plasmid
DNA exchange in nature is well documented in
B.
thuringiensis
strains and has been implicated as the
source of the remarkable diversity of
cry
genes
(Carlson and Kolst
ø
, 1993). Other comparisons of soil
isolates of
B. cereus
and
B. thuringiensis
strains,
selected with no regard for insect toxicity, have
demonstrated extensive chromosomal DNA exchange
with no apparent clonal population structure (Hu et al.,
2004). On the other hand, correlation persisted for the
highly conserved phenotypes like biochemical
properties and genotypes such as 16S rRNA etc. as
these are regulated by the in house conserved genes.
The number of available
cry
genes among these
strains was also variable. It can, therefore, be said that
Fig. 6 Comparison of relatedness between the
Bt
strains determined by 16S rRNA gene sequence, biochemical properties, RAPD
genotyping and availability of
cry
genes.
the report of conformity between phylogenetic
and phenotypic i.e. biotype or serotype (biotype in
this case) relatedness (Shishir et al., 2014) was also
evidenced in this study though RAPD- genotyping and
cry
gene profile did not follow the pattern.
2 Materials and methods
2.1 Bacterial strains and growth conditions
Indigenous
Bt
strains (n=177) preserved at
Bt
resource Centre
in the Department of Microbiology, University
of Dhaka and the reference
Bt
kurstaki
HD-73,
Bt
sotto
T84A1 and
Bt
japonensis
Buibui strains
collected from
Bt
stock collection of Okayama University,
Japan were used in this study. LB agar (per litre: tryptone
10 g, yeast extract 5 g, NaCl 10 g, agar 15 g) and LB
broth were used for culture maintenance, propagation and
subculture throughout the study.
2.2 Total DNA extraction
Total DNA was extracted from the indigenous
Bt
