Distribution Of The Endosymbionts In Cicadas(Hemiptera: Cicadidae)

Cicadas feed exclusively on plant xylem sap, and the nutrients in their diets are extremely unbalanced. Endosymbionts play an essential role in provisioning nutrients and the development of the cicadas. Usually, endosymbionts of cicadas are harbored in organ-like structures called bacteriomes. However, the bacterial diversity of bacteriomes in most cicadas remains unknown, and little is documented about the bacterial communities in other organs of cicadas such as the alimentary canal, salivary glands, Malpighian tubules, testes, and ovaries, etc. The bacterial communities were investigated in this thesis by using 16 S rRNA-PCR restriction fragment length polymorphism(RFLP) method, which were associated with Malpighian tubules and ovaries of different cicadas(Cryptotympana atrata(Fabricius), Hyalessa maculaticollis(Motschulsky), Karenia caelatata Distant, and Subpsaltria yangi Chen), and with various organs and intestinal regions of the cicada Hyalessa maculaticollis(Motschulsky). The results are as follows:1. Bacterial composition and diversity among the Malpighian tubules of the three representative cicada species(C. atrata, K. caelatata, and H. maculaticollis) were clearly different. Six bacteria belonging to the Phyla Gammaproteobacteria and Actinobacteria were detected in the Malpighian tubules of C. atrata. In H. maculaticollis, only two bacterial species belonging to Gammaproteobacteria were detected from their Malpighian tubules. In K. caelatata, four bacterial species were detected in the Malpighian tubules, among which one predoniment species belongs to the Alphaproteobacteria, while the other three bacteria belong to the Gammaproteobacteria.2. The endosymbiont Candidatus Sulcia muelleri was detedcted in the bacteriomes of all the three cicadas(S. yangi, C. atrata, and H. maculaticollis), which belongs to the phylum Bacteroidetes. In the bacteriomes of C. atrata and S. yangi, only the endosymbiont Ca. Sulcia muelleri was detected. Thirteen bacterial species were detected in the bacteriomes of H. maculaticollis, among which the Ca. Sulcia muelleri accounted for 5.5% of the clone library.3. Bacterial communities vary across different organs of H. maculaticollis, but they had similar dominant bacterial species.(1) Seven bacteria were detected in the salivary glands, which belong to the Phyla Proteobacteria and Firmicutes. The bacterial community was dominated by Pseudomonas aeruginosa and Enterobacter sp., and each of them accounted for 48.7% in the clone library. In total, the other five bacterial species together accounted for 2.05% of the clone library.(2) Twelve species were detected in the clone library of oesophagus, which belong to the phyla Proteobacteria, Firmicutes, Deinococcus-Thermus, and Bacteroidetes, respectively. Enterobacter cancerogenus was the most dominant bacterium, accounting for 46.28%. Pseudomonas aeruginosa was the second, accounting for 33.88%. The other 10 bacterial species were discovered at very low levels, in total accounting for 19.84%. Nine species of the phylum Proteobacteria were detected in the clone library of “filter chamber + conical segment”. E. cancerogenus was the most dominant bacterium, accounting for 38.36%. Enterobacter sp. was the second, accounting for 35.77%. Ps. aeruginosa was the third, accounting for 18.53%. The other 6 bacterial species were discovered at very low levels, in total accounting for 7.34%. Four species, all belonging to the phylum Gammaproteobacteria, were detected in the clone library of midgut loop, with E. cancerogenus accounting for 0.87%, Ps. aeruginosa accounting for 2.61%, Pantoea agglomerans accounting for 95.22%, and Pantoea sp. accounting for 1.30%. Three species belonging to the phylum Gammaproteobacteria were detected in the ileum, with E. cancerogenus accounting for 1.39%, P. aeruginosa accounting for 1.39%, and Pa. agglomerans accounting for 97.22%. Three species belonging to the phylum Gammaproteobacteria were detected in the “peritoneal sheath + rectum”, with Ps. aeruginosa accounting for 0.97%, Pa. agglomerans accounting for 97.58%, and Sodalis glossinidius accounting for 1.45%.(3) In the clone library of Malpighian tubules, two species of the Gammaproteobacteria were detected in the clone library, i.e., Enterobacter sp. accounting for 91.15% and P. aeruginosa accounting for 9.65%.(4) Thirteen species were detected in the bacteriomes, which belong to the phyla Deinococcus-Thermus, Betaproteobacteria, Actinobacteria and Bacteroidetes, respectively. The bacterial community was dominated by Meiothermus cerbereus(accounting for 32.5%) and Caldimonas hydrothermale(accounting for 21.5%). Ca. Sulcia muelleri accounted for 5.5% of the clone library. Other bacterial species were discovered at very low levels, in total accounting for 46% of the clone library.(5) Six bacterial species were detected in the testes. They belong to the phyla Bacteroidetes, Actinobacteria, Proteobacteria, and Deinococcus-Thermus, respectively. Ca. Sulcia muelleri was the most dominant bacterium, accounting for 89.06% of the clone library. The other five bacterial species were discovered at very low levels, in total accounting for 10.94%. In the clone library of ovaries, only the endosymbiont Ca. Sulcia muelleri was detected.The results indicated that the composition of bacterial communities in examined organs of cicadas were relatively simple and usually dominated by two or three bacterial species. The endosymbiont Ca. Sulcia muelleri was only detected in the bacteriomes, testes, and ovaries of cicadas.