Synergistic Effect Of Intestinal Bacterium MB1 To The Insecticidal Activity Of Bacillus Thuringiensis Toward Bombyx Mori

Bacillus thuringiensis (Bt) is a Gram-positive bacterium, which can generate parasporal crystal protein during the formation of spore. In these years, the researchers have done a lot of study about the improvement of insecticidal activity and made a series of progress. At the same time, the researchers proposed the different models of insecticidal mechanism of Bt, such as sepsis model. Recently, some researchers have proposed intestinal bacteria have important effection on the insecticidal activity of Bt. In other words, intestinal bacteria have a synergistic or inhibitory effect on the activity of Bt insecticide. The perspective about intestinal bacteria is controversial, and the mechanism of effect about intestinal bacteria remains unclear. This paper contrasted the intestinal bacteria separated from Bombyx mori on the impact of the insecticidal activity of Bt. We obtained a strain intestinal bacterium MB 1 which can improve the insecticidal activity of Cry toxin to B. mori. In addition, we have done preliminary study about the synergistic mode of action of MB1, which can lay the foundation for clarifying the mechanism of synergism of MB1 and improve the insecticidal activity of Bt insecticide in practice.1. By disinfecting the eggs of B. mori and rearing aseptically, we obtained sterile B. mori which was untreated with antibiotics. The sterile B. mori is basic material to obtain the effect of intestinal bacteria to Cry toxin and the subsequent research.2. By bioassay, we found the intestinal bacterium MB1, which can enhance the insecticidal activity of Bt. In addition, we analyzed the effect of antibiotics to the mortality of B. mori to Cry toxin. Antibiotics can reduce the sensitivity of B. mori to Cry toxin, and lead to the lower mortality of B. mori and slower death speed of B. mori. The spore from BMB171 had no impact on B. mori, but both the spore and MB1 had the synergism to Cry toxin, and the specific mechanism remains unclear.3. In order to understand the model of the synergistic effect of MB1, we studied the colonization of intestinal bacteria in the B. mori. and the result showed the synergistic effect was not due to the largest number of colonized MB 1, but may be associated with the characteristic of MB 1. Then, we compared the effect of MB 1 to the protoxin of Cry and the actived Cry toxin, and found MB1 had no significant influence on the actived Cry toxin. So, we concluded that the MB1 played an important role in the activation of protoxin.4. We investigated the growth of MB1 and BMB171 in the hemolymph of B. mori. The results showed that both MB1 and BMB171 can proliferate in the hemolymph of B. mori, it may be associated with the synergy of MB1 and the pathogenicity of Bt.5. We injected the different numbers of BMB171 and MB1 into the hemolymph of B. mori, and observed the mortality for B mori. The results showed that the injection of BMB 171 generated higher mortality than MB1, and the mortality of B. mori correlated with the number of bacteria. In summary, the synergistic effect of MB1 for the insecticidal activity of Bt may be related to the growth of MB1 in the hemolymph and a certain number of bacteria can cause the death of B. mori.