Microbes Isolated from Ailanthus altissima Leaves Contribute to Samia cynthia's Tolerance to the Toxic Quassinoid Diterpenoid.

Plants participate in complex interactions with microorganisms, co-evolving through specific chemical signaling pathways. Notably, some microorganisms associated with plants may also be acquired by herbivorous insects and potentially contribute to the insect's fitness. Here, we found that when the toxic plant, Ailanthus altissima, is consumed by silkworms (Samia cynthia), it can significantly alter the assembly of microbial community in S. cynthia midgut, particularly affecting members of Enterobacteriaceae and Bacillaceae families. And a main defensive quassinoid diterpenoid 6α-3,4-epoxy-tigloyloxychaparrin (6α-ETC) present in A. altissima leaves was found to promote the growth of Priestia sp. WY-1 (Bacillaceae). Furthermore, Salmonella sp. WY-7, WY-10 (Enterobacteriaceae), and Pseudomonas sp. WY-5 (Pseudomonadaceae), which were also isolated from S. cynthia midgut, demonstrated the ability to degrade 6α-ETC to a certain extent. Surprisingly, after PCR verification, that the midgut bacteria identified as Priestia sp. and Pseudomonas sp. could be traced back to their origin in A. altissima leaves. These results suggest that S. cynthia can acquire bacteria from A. altissima leaves, and that some of these shared microbes in the families of Enterobacteriaceae, Pseudomonadaceae, and Bacillaceae could contribute to the detoxification of quassinoid diterpenoid, potentially aiding the insect's tolerance to its toxic host plant. This study provides a foundation for studying the interactions between microorganisms, plants and insects.