1, lane 4 and lane 5). And both bands (c. 39 and 46.5 kDa) were present in the supernatants of induced cultures of BL (Bi; Fig. 1, lane 3). It indicated that both Plu1961 and Plu1962 were expressed as soluble proteins in BL21 (DE3), no matter whether they were separately expressed or co-expressed. When Plu1961/Plu1962 was applied by mixing with diet, neither mortality nor growth inhibition of both H. armigera and S. exigua larvae was observed within the tested amounts
(15–150 μL) of BL (Bi) lysate. However, injection of 10 μL of supernatant of BL (Bi) lysate resulted in around 42% mortality of S. exigua fourth-instar larvae after 24 h. And the mortality rate rose click here with the increase in BL (Bi) lysate volume. When 100 μL of concentrated
supernatant of BL (Bi) lysate was injected into S. exigua fourth-instar larvae, 97% mortality rate was observed after 24 h (Fig. 2b). When compared with the control group (supernatant of BL21 (DE3) lysate and heat-inactivated supernatant of BL (Bi) lysate), the supernatant of BL (Bi) lysate caused extensive blackening of larvae (Fig. 2a). Blackening of S. exigua larvae suggested that injection of BL (Bi) lysate PD0325901 in vivo resulted in the activation of phenoloxidase which was responsible for the synthesis of melanin, a key component in arthropod immunity and wound healing (Li et al., 2008). It demonstrated that Plu1961/Plu1962 had injectable toxicity against tested insect larvae, but no oral toxicity. MTT assay was performed
against insect midgut CF-203 cells to investigate the cytotoxicity of Plu1961/Plu1962. Neither component of binary toxin could affect the growth of CF-203 cells even after 4 days of incubation. In contrast, the mixture of Plu1961/Plu1962 caused a loss of cell viability after 24 h of incubation within the tested concentrations (0.2–1.6 μmol L−1). 0.2 μmol L−1 of binary toxin mixture resulted in 55% loss of cell viability. More than 90% of cells lost viability after treatment with 1.6 μmol L−1 of binary toxin (Fig. 2c). When compared with control cells (Fig. 3a), CF-203 cells treated with the mixture of Plu1961/Plu1962 showed Acesulfame Potassium marked swelling, formation of surface blisters, followed by membrane lysis and dispersal of the cytoplasmic organelles and swollen nuclear contents into the surrounding medium (Fig. 3d). In contrast, individual application of Plu1961 or Plu1962 alone had no morphological effect on CF-203 cells (Fig. 3b and c). Morphological changes in CF-203 cells exposed to Plu1961/Plu1962 mixture were further investigated by confocal microscope. The control cells and cells treated by Plu1961 alone displayed strong green fluorescence (microtubules) around the nuclei (strong blue fluorescence), the mitochondria (red fluorescence) appeared to be almost evenly distributed in the cytoplasm (Fig. 4a and b). In contrast, cells treated with the mixture of Plu1961/Plu1962 lost virtually all green and red fluorescence and exhibited only blue fluorescence (Fig. 4d).