Bt protein, produced by Bacillus thuringiensis, can bind receptors to destroy the physiological functions of the insect midgut. It is unknown whether Bt can also target the hindgut and influence its defense against fecal bacteria. Here we show that Crystal protein 1Ab (Cry1Ab), a Bt protein, was detected in the larval hindgut contents of Bombyx mori after ingestion of this toxin protein. The number of fecal bacteria that can be inhibited by the hindgut prophenoloxidase-induced melanization was significantly enhanced after oral ingestion of Cry1Ab. Although the hindgut contents became brown, the activity of hindgut phenoloxidase was decreased. LC-MS/MS analysis of the hindgut lumen contents revealed that many new proteins including several proteases were newly secreted. The enhanced secretion of proteases cleaved prophenoloxidase to decrease its activity, including the corresponding activity to inhibit the fecal bacteria. In addition, after ingestion of Cry1Ab, the pylorus (between the midgut and hindgut) could not autonomously contract due to the physical detachment of the acellular cuticle-like membrane from the epidermal cells, which prevented the movement of food from the midgut to the hindgut. Some cells in the cryptonephry of the hindgut became swollen and degraded, possibly due to the presence of Cry1Ab in the hindgut. These findings demonstrate that the inhibition of feces bacteria by the hindgut prophenoloxidase-induced melanization is out of control after Cry1Ab ingestion.

苏云金芽孢杆菌产生的Bt蛋白可以结合受体破坏昆虫中肠的生理功能。目前尚不清楚 Bt 是否也可以靶向后肠并影响其对粪便细菌的防御。在这里，我们表明在家蚕幼虫后肠内容物中检测到晶体蛋白 1Ab (Cry1Ab)，一种 Bt 蛋白摄入这种毒素蛋白后。口服 Cry1Ab 后，可被后肠酚氧化原酶诱导的黑化抑制的粪便细菌数量显着增加。虽然后肠内容物变成褐色，但后肠酚氧化酶活性降低。后肠腔内容物的 LC-MS/MS 分析表明，新分泌了许多新蛋白质，包括几种蛋白酶。蛋白酶分泌的增强会裂解酚氧化酶原以降低其活性，包括相应的抑制粪便细菌的活性。此外，在摄入 Cry1Ab 后，由于脱细胞角质层样膜与表皮细胞的物理分离，幽门（中肠和后肠之间）无法自主收缩，这阻止了食物从中肠到后肠的运动。后肠隐肾中的一些细胞肿胀和降解，可能是由于后肠中存在 Cry1Ab。这些发现表明，在摄入 Cry1Ab 后，后肠酚氧化原酶诱导的黑色素化对粪便细菌的抑制失控。