Preliminary Studies On The Compositions And Functions Of Microbiota From Adult And Larval Gut Of Two Leptopilina Wasps

In nature,insects are the most abundant species in animal groups.During a long period of coevolution,insects have evolved a close and mutually beneficial relationship with their gut microbiota.Insect gut microbiota can regulate many aspects of the host,such as nutrition,metabolism,immunity,development,reproduction and so on.Parasitoids are a kind of parasitic insects and are widely used to biocontrol agricultural pests.However,the studies of gut microbiota of parasitoids are very limited.Therefore,we take Leptopilina boulardi and Leptopilina heterotoma as the research objects,and study the taxonomic compositions and functions of microbiota from these two parasitoids.The results are summarized below:1.The taxonomic compositions and relative abundance of microbiota from the adults and larval guts of L.boulardi and L.heterotoma.Through metagenomic analysis,we found that bacteria,especially Proteobacteria,were the dominant microbe species in the adults and larval guts of these two parasitoids.There was a big difference on the type of dominant bacteria from larval guts between L.boulardi and L.heterotoma.The dominant genera in L.boulardi were Acetobacter and Caulobacter,while L.heterotoma was dominated by Sphingobium and Sphingopyxis.Strikingly,the dominant bacteria of adult females between L.boulardi and L.heterotoma were the same,which were Acetobacter and Sphingobium.A comparative analysis of the bacterial diversity revealed that the bacterial species numbers in the larval guts of these two parasitoids were much more than that in the adult females,especially in L.heterotoma,the number of the larval guts were almost twice that of adult females.After KEGG functional annotation of the metagenomes,we found that the data from these two parasitoids all annotated some important metabolic pathways,including carbohydrate metabolism,amino acid metabolism,energy metabolism and lipid metabolism.In addition,we found that Acetobacter was possibly involved in those metabolic pathways.Similarly,COG functional annotation results revealed that relatively high abundance of [E] Amino acid transport and metabolism and [C] Energy production and conversion in all metagenomic samples.Besides,CAZyme functional annotation results showed that the main CAZyme in adult females and larval guts of two parasitoids were Glycoside Hydrolases(GHs),Glycosyl Transferases(GTs)and Carbohydrate Esterases(CEs),which gives us some hints for the future research on microbial carbohydrate metabolism mechanism.2.The dominant cultivable bacteria from L.boulardi and L.heterotoma.By isolation and culture in vitro,we obtained two dominant bacteria from L.boulardi and L.heterotoma,which were Acetobacter pomorum and Lactobacillus fructivorans.Moreover,combining with the results of bacterial genome information,we found two strains of A.pomorum from the two parasitoids,which were A.pomorum SH and A.pomorum BDGP5.Interestingly,their host Drosophila also had the same two A.pomorum strains.In addition,we found that A.pomorum SH showed high abundance comparing to A.pomorum BDGP5.3.The effects of A.pomorum on the development of parasitoids.After parasitizing germ-free Drosophila,most of the parasitic wasp larvae died in their fourth instar and could not successfully pupae and emergence,suggesting that the microbes in host Drosophila are important for the development of parasitic wasps.Further results revealed that feeding A.pomorum BDGP5 and A.pomorum SH to germ-free Drosophila can rescue the development of some parasitic wasp larvae to develop through fifth instar,pupae and finally emerge from the host pupal shell.However,feeding L.fructivorans did not help the development of L.boulardi.Further research found that mixing 1% acetic acid in sterile food also had a significant recovery effect on the development of L.boulardi.These results indicate that both A.pomorum and its metabolic product,acetic acid,play an important role on the development of parasitic wasps.In summary,we found two strains of A.pomorum in both adult females and larval guts of these two parasitoids,which were A.pomorum SH with high abundance and A.pomorum BDGP5 with low abundance.Meanwhile,both A.pomorum and acetic acid were essential for the development of larvae of these two parasitoids.Our research provides us some hints that we may utilize some symbiotic bacteria to enhance the survival of parasitiods.