JoVE Logo
Autorzy
Skontaktuj Się z Nami

Zaloguj się

Aby wyświetlić tę treść, wymagana jest subskrypcja JoVE. Zaloguj się lub rozpocznij bezpłatny okres próbny.

W tym Artykule

  • Podsumowanie
  • Streszczenie
  • Wprowadzenie
  • Protokół
  • Wyniki
  • Dyskusje
  • Ujawnienia
  • Podziękowania
  • Materiały
  • Odniesienia
  • Przedruki i uprawnienia

Podsumowanie

To obtain an axenic insect, its egg surface is sterilized, and the hatched larva is subsequently reared using axenic leaves. This method provides an efficient way for axenic insect preparation without administering antibiotics or developing an artificial diet, which can also be applied to other leaf-eating insects.

Streszczenie

Insect guts are colonized by diverse bacteria that can profoundly impact the host's physiological traits. Introducing a particular bacterial strain into an axenic insect is a powerful method to verify gut microbial function and elucidate the mechanisms underlying gut microbe-host interactions. Administering antibiotics or sterilizing egg surfaces are two commonly used methods to remove gut bacteria from insects. However, in addition to the potential adverse effects of antibiotics on insects, previous studies indicated that feeding antibiotics could not eliminate gut bacteria. Thus, germ-free artificial diets are generally employed to maintain axenic insects, which is a tedious and labor-intensive process that cannot fully resemble nutritional components in natural food. Described here is an efficient and simple protocol to prepare and maintain axenic larvae of a leaf beetle (Plagiodera versicolora). Specifically, surfaces of the beetle eggs were sterilized, following which germ-free poplar leaves were used to rear axenic larvae. The axenic status of the insects was further confirmed via culture-dependent and culture-independent assays. Collectively, by combining egg disinfection and germ-free cultivation, an efficient and convenient method was developed to obtain axenic P. versicolora, providing a readily transferable tool for other leaf-eating insects.

Wprowadzenie

Similar to mammals, the insect digestive tract is a cavity for food digestion and absorption. Most insects harbor diverse commensal bacteria that thrive in their guts and live on nutrition supplied by hosts1. The gut commensal community has a profound impact on multiple physiological processes in insects, including food digestion and detoxification2,3,4, nutrition and development5,6,7, defense against pathogens and parasites8,9,10,11, chemical communication12,13 and behaviors14,15. Intriguingly, some gut microbiota can be facultatively pathogenic or be manipulated by invading pathogens to aggravate infection, indicating that gut bacteria can be harmful in some cases16,17,18. Gut bacteria can also serve as a microbial resource for biotechnical applications and pest management. For example, lignocellulose-digesting bacteria from phytophagous and xylophagous insects were used to digest plant cells for developing biofuels19. The dispersal of engineered gut symbionts expressing bioactive molecules is a novel and promising tactic to manage agriculture and forestry pests and mosquitoes transmitting infectious diseases19,20,21, which can also be used to improve the fitness of beneficial insects22. Illustrating how a gut bacterium behaves in vivo is thus considered a priority to fully leverage its function and further exploit it for various applications.

Animals can harbor 1 to >1000 symbiotic microbial species in the gut1. As a result, it is difficult to accurately verify how individual bacterial taxa or their assembly perform inside an animal, and whether the host or its microbial partners drive a specific function. Therefore, preparing axenic larvae to obtain gnotobiotic insects by mono- or multi-species colonization is necessary to investigate bacterial function and interaction with insects23. At present, administering antibiotic cocktails and sterilizing the surface of insect eggs are common methods to remove gut bacteria14,24,25,26. However, antibiotic diets cannot eliminate gut bacteria completely and have a negative effect on host insect physiology27,28. Consequently, the use of antibiotic-treated insects may obscure the true abilities of some gut bacteria. Fortunately, surface sterilization of eggs can negate this problem23,29, which has no or negligible effects on experimental insects. Furthermore, artificial diets cannot fully resemble natural insect food, and developing an artificial diet is a costly and labor-consuming process30,31.

The willow leaf beetle, Plagiodera versicolora (Laicharting) (Coleoptera: Chrysomelidae), is a widespread leaf-eating pest that mainly feeds on salicaceous trees, such as willows (Salix) and poplar (Populus L.)32,33. Here, the willow leaf beetle was used as a representative leaf-eating insect to develop a protocol to prepare and rear a germ-free insect. We exploited plant tissue culture to obtain germ-free poplar leaves to rear P. versicolora axenic larvae from sterilized eggs. The axenic status of P. versicolora larvae was verified via culture-dependent and culture-independent assays. This protocol can maintain axenic insects that better mimic the wild condition than insect rearing with an artificial diet. More importantly, this method is convenient at a very low cost, which increases the feasibility of obtaining axenic insects for future insect-gut microbiota interaction studies, especially for non-model insects without well-developed artificial diets.

Access restricted. Please log in or start a trial to view this content.

Protokół

1. Insect rearing

  1. Maintain the P. versicolora population in a growth chamber at the condition of 27 °C and 70 ± 5% relative humidity with a photoperiod of 16 h light/8 h dark. Place them in perforated plastic boxes with tiled wet absorbing paper and feed them fresh poplar branches. Spray clean water on absorbing paper to maintain moisture and change the branches every two days.
  2. Isolate adults for oviposition after pupation. Feed them tender leaves to obtain more eggs.
  3. Collect newly laid eggs (within 24 h). Place the eggs on moist absorbing paper for 60 h to prepare axenic larvae.
    ​NOTE: Newly laid eggs will hatch after ~72 h. The best time to sterilize egg surfaces is the day before hatching; otherwise, the number of successfully hatched eggs will decrease.

2. Germ-free poplar culturing

  1. Prepare Murashige and Skoog (MS) medium and 1 mg/mL α-naphthalene acetic acid (NAA) stock solutions (see the Table of Materials).
  2. In a biosafety hood, add 50 µL of 1 mg/mL NAA stock solution to 500 mL of MS medium, shake to mix well, and pour ~50 mL per tissue culture container and wait for solidification.
  3. Prepare scalpels, alcohol lamp, and forceps; sterilize the scalpels and forceps in the alcohol lamp flame in the biosafety hood.
  4. Cut 3-4 cm stem segments with apical buds or lateral buds from poplar seedlings at ~1 month of growth (germ-free tissue-cultured seedlings), and insert them into the culture medium, one or two stem segments per container.
  5. Incubate these stem segments in a growth chamber at 25 °C and 50 ± 10 cd light intensity with a photoperiod of 16 h light/8 h dark for approximately 30 days. Use the germ-free leaves to feed the axenic larvae.

3. Egg surface sterilization and rearing axenic larvae

  1. Autoclave Petri dishes, paintbrushes, filter paper, distilled water, and a Petri dish containing LB (Luria-Bertani) agar medium.
  2. Place leaves with adherent eggs in a Petri dish, carefully remove the eggs from the leaves using forceps, and transfer them to another Petri dish.
    NOTE: This step should be performed very carefully because the eggs are adherent to the leaves.
  3. Wash these eggs with 75% ethanol for 8 min, and repeat the wash four times with sterile water.
  4. Transfer the eggs onto LB agar medium to preserve moisture for hatching.
    NOTE: Using LB agar medium can help to verify whether the disinfected egg is germ-free.
  5. Place the Petri dish in a growth chamber and wait for the eggs to hatch within 24 h.
  6. In a biosafety hood, tile three pieces of wet filter paper in a Petri dish, place germ-free poplar leaves on the paper, collect the larvae and place them on the leaves, seal the Petri dish with parafilm, and incubate them in a growth chamber at 27 °C and 70 ± 5% relative humidity with a photoperiod of 16 h light/8 h dark.
    NOTE: The tissue-cultured leaves are delicate and can lose water quickly. Thus, using moist filter paper is necessary when transferring the leaves to the Petri dish.
  7. Change the leaves every two days.
  8. For the conventionally reared groups, transfer the eggs from the leaves to a Petri dish containing moist filter paper and feed these larvae with germ-free poplar leaves.

4. Verification of axenic larvae with culture-dependent assays

  1. Randomly select three 1st, 2nd, and 3rd instar larvae from the germ-free and conventionally reared groups.
  2. Dissect the 3rd instar larvae with sterile scissors and forceps under a stereomicroscope and collect their guts in microcentrifuge tubes. Collect intact 1st and 2nd instar larvae in tubes.
    NOTE: Collect whole 1st and 2nd instar larvae as they are too small to dissect, and keep their guts intact.
  3. Add 100 µL of phosphate-buffered saline and three steel balls to 1.5 mL tubes and grind the tissues into homogenates using a bead-beating homogenizer.
  4. Add 100 µL of the homogenate to LB agar medium and plate using a sterile glass spreading rod.
  5. Place the plates at 37 °C for 24 h and observe the bacterial colonies.

5. Verification of axenic individuals with culture-independent assays

  1. Extract the total DNA of tissues (obtained in section 4) using a DNA extraction kit.
  2. Measure DNA concentration using a spectrophotometer at 260 nm.
  3. Amplify the bacterial 16S rRNA gene using universal 16S rRNA primers with PCR. Set up the reaction system with 18 µL of 1.1x PCR master mix (see the Table of Materials), 0.5 µL of 27F primer (5'-ACGGATACCTTGTTACGAC-3'), 0.5 µL of 1495R primer (5'-ACGGATACCTTGTTACGAC-3') and 100 ng template DNA. Set the PCR conditions at 95 °C for 3 min; 28 cycles of 95 °C for 30 s, 55 °C for 1 min, and 72 °C for 1 min; followed by 72 °C for 10 min. Store the PCR products at 4 °C until further analysis.
  4. Mix the PCR products with nucleic acid dye and analyze them using electrophoresis on a 1% agarose gel in 1x TAE buffer. Use 10 µL of a DNA marker as a reference.
  5. Observe the gel with a UV transilluminator and look for the target fragment around 1,500 bp.

Access restricted. Please log in or start a trial to view this content.

Wyniki

The life stages of P. versicolora are shown in Figure 1. The adult male is smaller than the adult female (Figure 1A). In the field, the beetle clusters its eggs on a leaf; here, four eggs were detached from a leaf (Figure 1B). The poplar stem segments and seedlings used for axenic insect rearing are shown in Figure 2. The gut of a 3rd instar larva is shown in Fig...

Access restricted. Please log in or start a trial to view this content.

Dyskusje

Preparation of germ-free larvae and obtaining gnotobiotic larvae by reintroducing specific bacterial strains are powerful methods to elucidate the mechanisms underlying host-microbe interactions. Newly hatched larvae obtain gut microbiota in two main ways: vertical transmission from the mother to the offspring or horizontal acquisition from siblings and the environment34. The former can be fulfilled by parental transfer to the offspring through contamination of the egg surface35<...

Access restricted. Please log in or start a trial to view this content.

Ujawnienia

The authors have no conflicts of interest to disclose.

Podziękowania

This work was funded by the National Natural Science Foundation of China (31971663) and the Young Elite Scientists Sponsorship Program by CAST (2020QNRC001).

Access restricted. Please log in or start a trial to view this content.

Materiały

NameCompanyCatalog NumberComments
0.22 µm syringe filtersMilliporeSLGP033RB
1 mg/mL NAA stock solutiona. Prepare 0.1 M NaOH solution (dissolve 0.8 g NaOH in 200 mL of distilled water).
b. Add 0.2 g NAA in a 250 mL beaker, add little 0.1 M NaOH solution until NAA dissolved, and adjust the final volume to 200 mL with distilled water.
c. Filter the solution to remove bacteria with a 0.22 µm syringe filter and a 50 mL sterile syringe, subpackage the solution in 1.5 mL centrifuge tubes and restore at -20 °C.
1.5 mL microcentrifuge tubesSangon BiotechF600620
10x PBS stock solutionBiosharp Life SciencesBL302A
2 M KOH solutionDissolve 22.44 g KOH (molecular weight: 56.1) in 200 mL of distilled water and autoclave it for 20 min at 121 °C.
250 mL and 2,000 mL beakersShubosb16455
50 mL sterile syringesJintaJT0125789
500 mL measuring cylinderShubosb1601
50x TAE stock solutiona. Dissolve 242 g Tris and 18.612 g EDTA in 700 mL of distilled water.
b. Adjust pH to 7.8 with about 57.1 mL of acetic acid.
c. Adjust the final volume to 1,000 mL.
d. The stock solution was diluted to 1x TAE buffer when used.
75% ethanolXingheda trade
α-naphthalene acetic acid (NAA)Solarbio Life Sciences86-87-3
Absorbing paper22.3 cm x 15.3 cm x 9 cm
Acetic acidSinopharm Chemical Reagent Co. Ltd
AgarCoolaber9002-18-0
AgaroseBiowest111860
AutoclavePanasonicMLS-3781L-PC
Bead-beating homogenizerJing XinXM-GTL64
DNA extraction kitMP Biomedicals116560200
EDTASaiguo Biotech1340
Filter paperJiaojie70 mm diameter
Gel electrophoresis unitBio-rad164-5052
Gel Signal Green nucleic acid dyeTsingKeTSJ003
Germ-free poplar seedlingsShan Xin poplar from Ludong University in Shandong Province
Golden Star Super PCR Master Mix (1.1×)TsingKeTSE101
Growth chamberRuihuaHP400GS-C
LB agar mediuma. Dissolve 5 g tryptone, 5 g NaCl, 2.5 g yeast extract in 300 mL of distilled water.
b. Adjust the final volume to 500 mL, transfer the solution to a 1,000 mL conical flask, and add 7.5 g agar.
c. Autoclave the medium for 20 min at 121 °C.
Mini centrifugeDRAGONLABD1008
MS basic mediumCoolaberPM1121-50LM0245
MS solid medium for germ-free poplar seedling culturea. Dissolve 4.43 g MS basic medium powder and 30 g sucrose in 800 mL of distilled water.
b. Adjust the pH to about 5.8 with 2 M KOH by a pH meter.
c. Adjust the final volume to 1,000 mL, separate into two parts, transfer into two 1,000 mL conical flasks, and add 2.6 g agar per 500 mL.
d. Autoclave for 20 min at 121 °C.
NanoDrop 1000 spectrophotometerThermo Fisher Scientific
Paintbrush1 cm width, used to collect the eggs
ParafilmBemisPM-996
PCR Thermal CyclersEppendorf6331000076
Petri dishesSupin90 mm diameter
pH meterMETTLER TOLEDOFE20
Pipettes 0.2-2 µLGilsonECS000699
Pipettes 100-1,000 µLEppendorf3120000267
Pipettes 20-200 µLEppendorf3120000259
Pipettes 2-20 µLEppendorf3120000232
Plant tissue culture containerChembaseZP21240 mL
Plastic box2.35 L
Potassium hydroxide (KOH)Sinopharm Chemical Reagent Co. Ltd
Primers for amplifying the bacterial 16S rRNA geneSangon Biotech27-F: 5’-ACGGATACCTTGTTACGAC-3’, 1492R: 5’-ACGGATACCTTGTTACGAC-3’
Sodium chloride (NaCl)Sinopharm Chemical Reagent Co. Ltd
Sodium hydroxide (NaOH)Sinopharm Chemical Reagent Co. Ltd
Steel balls0.25 mmused to grind tissues
StereomicroscopeOLYMPUSSZ61
SucroseSinopharm Chemical Reagent Co. Ltd
Trans2K plus II DNA markerTransgene BiotechBM121-01
Tris baseBiosharp Life Sciences1115
TryptoneThermo Fisher Scientific LP0037
UV transilluminatorMonad BiotechQuickGel 6100
VortexerScilogexMX-S
Willow branchesSha Lake Park, Wuhan, China
Willow leaf beetleHuazhong Agricultural University, Wuhan, China
Yeast extractThermo Fisher ScientificLP0021

Odniesienia

  1. Moran, N. A., Ochman, H., Hammer, T. J. Evolutionary and ecological consequences of gut microbial communities. Annual Review of Ecology, Evolution, and Systematics. 50 (1), 451-475 (2019).
  2. Warnecke, F., et al. Metagenomic and functional analysis of hindgut microbiota of a wood-feeding higher termite. Nature. 450 (7169), 560-565 (2007).
  3. Tokuda, G., et al. Fiber-associated spirochetes are major agents of hemicellulose degradation in the hindgut of wood-feeding higher termites. Proceedings of the National Academy of Sciences of the United States of America. 115 (51), 11996-12004 (2018).
  4. Wang, G. H., et al. Changes in microbiome confer multigenerational host resistance after sub-toxic pesticide exposure. Cell Host & Microbe. 27 (2), 213-224 (2020).
  5. Shin, S. C., et al. Drosophila microbiome modulates host developmental and metabolic homeostasis via insulin signaling. Science. 334 (6056), 670-674 (2011).
  6. Storelli, G., et al. Lactobacillus plantarum promotes Drosophila systemic growth by modulating hormonal signals through TOR-dependent nutrient sensing. Cell Metabolism. 14 (3), 403-414 (2011).
  7. Salem, H., et al. Vitamin supplementation by gut symbionts ensures metabolic homeostasis in an insect host. Proceedings. Biological Sciences. 281 (1796), 20141838(2014).
  8. Koch, H., Schmid-Hempel, P. Socially transmitted gut microbiota protect bumble bees against an intestinal parasite. Proceedings of the National Academy of Sciences of the United States of America. 108 (48), 19288-19292 (2011).
  9. Cirimotich, C. M., et al. Natural microbe-mediated refractoriness to Plasmodium infection in Anopheles gambiae. Science. 332 (6031), 855-858 (2011).
  10. Kaltenpoth, M., Gottler, W., Herzner, G., Strohm, E. Symbiotic bacteria protect wasp larvae from fungal infestation. Current Biology. 15 (5), 475-479 (2005).
  11. Yuan, C., Xing, L., Wang, M., Hu, Z., Zou, Z. Microbiota modulates gut immunity and promotes baculovirus infection in Helicoverpa armigera. Insect Science. , (2021).
  12. Dillon, R. J., Vennard, C. T., Charnley, A. K. Pheromones - Exploitation of gut bacteria in the locust. Nature. 403 (6772), 851(2000).
  13. Xu, L. T., Lou, Q. Z., Cheng, C. H., Lu, M., Sun, J. H. Gut-associated bacteria of Dendroctonus valens and their involvement in verbenone production. Microbial Ecology. 70 (4), 1012-1023 (2015).
  14. Schretter, C. E., et al. A gut microbial factor modulates locomotor behaviour in Drosophila. Nature. 563 (7731), 402-406 (2018).
  15. Jia, Y., et al. Gut microbiome modulates Drosophila aggression through octopamine signaling. Nature Communications. 12 (1), 2698(2021).
  16. Ma, M., et al. Metabolic and immunological effects of gut microbiota in leaf beetles at the local and systemic levels. Integrative Zoology. 16 (3), 313-323 (2021).
  17. Xu, L., et al. Synergistic action of the gut microbiota in environmental RNA interference in a leaf beetle. Microbiome. 9 (1), 98(2021).
  18. Xu, L., et al. Gut microbiota in an invasive bark beetle infected by a pathogenic fungus accelerates beetle mortality. Journal of Pest Science. 92, 343-351 (2019).
  19. Berasategui, A., Shukla, S., Salem, H., Kaltenpoth, M. Potential applications of insect symbionts in biotechnology. Applied Microbiology and Biotechnology. 100 (4), 1567-1577 (2016).
  20. Tikhe, C. V., Martin, T. M., Howells, A., Delatte, J., Husseneder, C. Assessment of genetically engineered Trabulsiella odontotermitis as a 'Trojan Horse' for paratransgenesis in termites. BMC Microbiology. 16 (1), 202(2016).
  21. Wang, S., et al. Fighting malaria with engineered symbiotic bacteria from vector mosquitoes. Proceedings of the National Academy of Sciences of the United States of America. 109 (31), 12734-12739 (2012).
  22. Leonard, S. P., et al. Engineered symbionts activate honey bee immunity and limit pathogens. Science. 367 (6477), 573-576 (2020).
  23. Kietz, C., Pollari, V., Meinander, A. Generating germ-free Drosophila to study gut-microbe interactions: protocol to rear Drosophila under axenic conditions. Current Protocols in Toxicology. 77 (1), 52(2018).
  24. Brummel, T., Ching, A., Seroude, L., Simon, A. F., Benzer, S. Drosophila lifespan enhancement by exogenous bacteria. Proceedings of the National Academy of Sciences of the United States of America. 101 (35), 12974-12979 (2004).
  25. Correa, M. A., Matusovsky, B., Brackney, D. E., Steven, B. Generation of axenic Aedes aegypti demonstrate live bacteria are not required for mosquito development. Nature Communications. 9 (1), 4464(2018).
  26. Romoli, O., Schonbeck, J. C., Hapfelmeier, S., Gendrin, M. Production of germ-free mosquitoes via transient colonisation allows stage-specific investigation of host-microbiota interactions. Nature Communications. 12 (1), 942(2021).
  27. Berasategui, A., et al. Gut microbiota of the pine weevil degrades conifer diterpenes and increases insect fitness. Molecular Ecology. 26 (15), 4099-4110 (2017).
  28. Lin, X. L., Kang, Z. W., Pan, Q. J., Liu, T. X. Evaluation of five antibiotics on larval gut bacterial diversity of Plutella xylostella (Lepidoptera: Plutellidae). Insect Science. 22 (5), 619-628 (2015).
  29. Muhammad, A., Habineza, P., Hou, Y., Shi, Z. Preparation of red palm weevil Rhynchophorus Ferrugineus (Olivier) (Coleoptera: Dryophthoridae) germ-free larvae for host-gut microbes interaction studies. Bio-protocol. 9 (24), 3456(2019).
  30. Gelman, D. B., Bell, R. A., Liska, L. J., Hu, J. S. Artificial diets for rearing the Colorado potato beetle, Leptinotarsa decemlineata. Journal of Insect Science. 1, 7(2001).
  31. Bengtson, D. A. A comprehensive program for the evaluation of artificial diets. Journal of the World Aquaculture Society. 24 (2), 285-293 (2007).
  32. Utsumi, S., Ando, Y., Ohgushi, T. Evolution of feeding preference in a leaf beetle: the importance of phenotypic plasticity of a host plant. Ecology Letters. 12 (9), 920-929 (2009).
  33. Ishihara, M., Ohgushi, T. Reproductive inactivity and prolonged developmental time induced by seasonal decline in host plant quality in the willow leaf beetle Plagiodera versicolora (Coleoptera: Chrysomelidae). Environmental Entomology. 35 (2), 524-530 (2006).
  34. Bright, M., Bulgheresi, S. A complex journey: transmission of microbial symbionts. Nature Reviews: Microbiology. 8 (3), 218-230 (2010).
  35. Hassan, B., Siddiqui, J. A., Xu, Y. Vertically transmitted gut bacteria and nutrition influence the immunity and fitness of Bactrocera dorsalis larvae. Frontiers in Microbiology. 11, 596352(2020).
  36. Hosokawa, T., et al. Obligate bacterial mutualists evolving from environmental bacteria in natural insect populations. Nature Microbiology. 1, 15011(2016).
  37. Habineza, P., et al. The promoting effect of gut microbiota on growth and development of red palm weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera: Dryophthoridae) by modulating its nutritional metabolism. Frontiers in Microbiology. 10, 1212(2019).
  38. Meilan, R., Ma, C. Poplar (Populus spp.). Methods in Molecular Biology. 344, Clifton, N.J. 143-151 (2006).
  39. Wani, Z. A., Ashraf, N., Mohiuddin, T., Riyaz-Ul-Hassan, S. Plant-endophyte symbiosis, an ecological perspective. Applied Microbiology and Biotechnology. 99 (7), 2955-2965 (2015).
  40. Grout, B. W. Meristem-tip culture. Methods in Molecular Biology. 6, Clifton, N.J. 81-91 (1990).

Access restricted. Please log in or start a trial to view this content.

Przedruki i uprawnienia

Zapytaj o uprawnienia na użycie tekstu lub obrazów z tego artykułu JoVE

Zapytaj o uprawnienia

Przeglądaj więcej artyków

Axenic InsectsGut MicrobiotaLeaf BeetleTissue Cultured SeedlingsGerm free LeavesHost gut InteractionPhysiological ProcessesMS MediumNAA Stock SolutionInsect RearingSurface sterilized EggsOvipositionPoplar BranchesSterilization ProtocolGrowth Chamber

This article has been published

Video Coming Soon

JoVE Logo

Prywatność

Warunki Korzystania

Zasady

Skontaktuj Się z Nami

Poleć Bibliotece

BIULETYNY JoVE

Badania

Edukacja

Autorzy

Bibliotekarze

O JoVE

Copyright © 2025 MyJoVE Corporation. Wszelkie prawa zastrzeżone