Basic HTML Version
Bt Research 2013, Vol.4 No.2 8-13
ISSN 1925-1939
http://bt.sophiapublisher.com
10
Figure 1 SDS-PAGE 10% of
Bt
strains toxic to
Simulium
spp.
Note: M=molecular marker, 1:
Bti
T 14001, 2:
Bti
S1785, 3:
S2271, 4: S2272, 5:
Bt medellin
163-0131, 6:
Bt jegathesan
T28 A001
According to data available at the website maintained
by Dr. Crickmore (Crickmore et al., 2010) strains of
B.
thuringiensis
subsp.
israelensis
can express the
proteins of approximately 135 kDa (Cry4Aa1,
Cry4Aa2, Cry4Aa3); 128 kDa (Cry4Ba1, Cry4Ba2,
Cry4Ba3, Cry4Ba4 and Cry4Ba5); 78 kDa (Cry10Aa1,
Cry10Aa2 and Cry10Aa3); 72 kDa (Cry11Aa1,
Cry11Aa2 and Cry11Aa3); 29 kDa (Cry60Aa2,
Cry60Ba2, Cyt1Aa1, Cyt1Aa5, Cyt1Aa2; Cyt1Ca1;
Cyt2Ba1, Cyt2Ba2 and Cyt2Ba9). The Cry4 and
Cry11 are the most toxic Cry proteins to
A. aegypti
(Chen et al., 2009; Fernandez et al., 2009).
Bt
medellin
was first isolated in Colombia and
presents high toxicity for some species of Culicidae
(Orduz et al., 1991; Restrepo et al., 1997).
According to Crickmore (2010), strains of serotype
medellin
can express proteins Cry11Bb1 (94 kDa),
Cry29Aa1, Cry30Aa1, and Cyt1Ab1 (27 kDa) and
Cyt2Bc1 (29.7 kDa).
Bt
jegathesan
was isolated in Malaysia and also shows
toxicity to the larvae of Culicidae (Kawalek et al.,
1995; Wirth et al., 2004). According to Crickmore
(2010) strains of serotype
jegathesan
may express
toxins Cry11Ba1 (81 kDa), Cry24Aa1 (75.9 kDa),
Cry25Aa1 (76 kDa), and Cry30Ca2, Cry60Aa1 and
Cyt2Bb1 (30 kDa). Work undertaken with
Bt
jegathesan
strain 367 and
Bt
medellin
strain
163~131 showed that although these strains are very
toxic to mosquito larvae, they are 10 times less toxic
than
Bt
israelensis
strains in laboratory conditions
(Thiery et al., 1999).
In several studies, serovar israelensis is reported to be
toxic to larvae of
Simulium
spp. (Myburgh and Nevill,
2003, Petry et al., 2004; Stoops and Adler, 2006), and
a non-agglutinating strain of
Bt
has also recently been
reported to have high toxicity against these insects
(Cavados et al., 2005), however, to date there are no
reports of the toxic activity of strains of serotypes
jegathesan
and
medellin
to blackflies.
The results of this study indicate that the Amazonian
strains are promising for blackfly control with similar
activities to those obtained with the strains of
Bt
serovar israelensis
. This study, along with previous
work (Cavados et al., 2005) also indicates that some
auto-agglutinating strains can have good activity
against these insects whereas strains of serotypes
medellin
and
jegathesan
significantly less effective for
controlling blackfly larvae.
2 Materials and Methods
2.1
Bacillus thuringiensis
strains
Strains used in this study were isolated from 200 soil
samples from the city of Manaus and its surroundings,
in the Amazon region. The isolation of strains was
performed at the Laboratory of Entomopathogenic
Bacteria of EMBRAPA Genetic Resources and
Biotechnology,
Brasília-DF/Brazil
using
the
methodology described by the World Health
Organization (WHO, 1987).
2.2 Selective bioassays against larvae of
Aedes
aegypti
and
Culex quinquefasciatus
To select the most toxic samples, we first carried out a
pre-selection of strains of
B. thuringiensis
from soil of
the Amazon by selective bioassay using larvae of
Aedes aegypti
(Linnaeus) and
Culex quinquefasciatus
Say (Diptera Culicidae), maintained at EMBRAPA
Genetic Resources and Biotechnology.
Strains were grown in EMBRAPA medium (Monnerat
et al., 2007) for 72 hours on shaker at 200 r/min and
28
℃
. After this time, optical microscopy was
performed to observe the structures (spores and
crystals). The bioassay was performed by placing 1
mL of sporulated culture in 100 mL of water in cups