The battle between gut bacteria, immune system and Cry1Ac toxin in Plutella xylostella.

Research into the interaction between Bacillus thuringiensis (Bt) and pest has primarily focused on the Cry toxin receptor, relatively less attention has been paid towards the role of the gut bacteria, particularly the mechanism on how insect gut bacteria affect its sensitivity to Bt. Addressing this gap could provide valuable insights for pest control strategies. This study analyzed the variances of gut microbiota between Cry1Ac-resistant and sensitive strains of Plutella xylostella, as well as field populations. From their gut microbiota, one strain (Enterobacter asburiae, PxG1) that significantly increased and another strain (Enterobacter hormaechei, PxG15) that significantly decreased the Cry1Ac susceptibility of P. xylostella were isolated and cultured. PxG15 degraded Cry1Ac protoxin and activated the proPO-AS and JNK pathway, which reduced Cry1Ac’s damage to the midgut while limiting the invasion of gut bacteria into the hemolymph. Although PxG1 rapidly activated the proPO-AS, the JNK pathway was activated in a much slower and weaker mode when compared to PxG15, which attenuated the repairing efficiency of midgut under the treatment of Cry1Ac, leading to death resulted from sepsis from the quick invasion of gut bacteria into the hemolymph. This study illustrates the intricate interrelationships among Cry1Ac toxins, the pest's midgut bacteria, and its immune system. Different midgut bacteria exhibited distinct interactions with the Cry1Ac toxin and the immune system, resulting in opposing effects on the virulence of Cry1Ac on pests. These findings provide new insights into the role of gut bacteria in influencing the survival of Lepidoptera pest after exposure to Cry1Ac.