Rearing the Fruit Fly Drosophila melanogaster Under Axenic and Gnotobiotic Conditions

Summary

A method for rearing Drosophila melanogaster under axenic and gnotobiotic conditions is presented. Fly embryos are dechorionated in sodium hypochlorite, transferred aseptically to sterile diet, and reared in closed containers. Inoculating diet and embryos with bacteria leads to gnotobiotic associations, and bacterial presence is confirmed by plating whole-body Drosophila homogenates.

Abstract

The influence of microbes on myriad animal traits and behaviors has been increasingly recognized in recent years. The fruit fly Drosophila melanogaster is a model for understanding microbial interactions with animal hosts, facilitated by approaches to rear large sample sizes of Drosophila under microorganism-free (axenic) conditions, or with defined microbial communities (gnotobiotic). This work outlines a method for collection of Drosophila embryos, hypochlorite dechorionation and sterilization, and transfer to sterile diet. Sterilized embryos are transferred to sterile diet in 50 ml centrifuge tubes, and developing larvae and adults remain free of any exogenous microbes until the vials are opened. Alternatively, flies with a defined microbiota can be reared by inoculating sterile diet and embryos with microbial species of interest. We describe the introduction of 4 bacterial species to establish a representative gnotobiotic microbiota in Drosophila. Finally, we describe approaches for confirming bacterial community composition, including testing if axenic Drosophila remain bacteria-free into adulthood.

Introduction

Most animals are intimately associated with bacteria ('microbiota') from birth to death¹. Comparisons of microorganism-free ('axenic') and microorganism-associated ('conventional') animals have shown microbes influence diverse aspects of animal health, including metabolic, nutritional, vascular, hepatic, respiratory, immunological, endocrine, and neurological function². The fruit fly Drosophila melanogaster is a key model for understanding many of these processes in the presence of microbes^3,4 and for studying microbiota influence on animal health^5,6. No bacterial species is present in every ....

Protocol

1. Culture Bacteria (Start ~1 Week before Picking Eggs)

1. Prepare modified MRS²⁰ (mMRS) plates and broth tubes (Table 1). Pour 20 ml mMRS agar into each 100 mm Petri plate and allow to cool/dry overnight, or 5 ml mMRS broth into 18 mm test tubes.
2. Streak Acetobacter pomorum, A. tropicalis, Lactobacillus brevis, and L. plantarum on mMRS agar plates. Incubate Acetobacter overnight at 30 °C. Incubate Lactobacillus anaerobically by placing the plates in an airtight container and flooding with carbon dioxide before sealing. Incubate at 30 °C overnight.
   Note....

Results

Successful rearing of axenic flies is confirmed by isolation of no CFUs from whole-body homogenizations of D. melanogaster adults (Figure 1). Alternatively, if the plated homogenate yields colonies, the vials are contaminated and should be discarded. For gnotobiotic flies, each of the four bacterial isolates were isolated from pools of 5 adult males, demonstrating differences in total viable CFUs associated with adult flies (Figure 1). Each bacte.......

Discussion

The method described here is one of several approaches for embryo dechorionation^{8,11,18,25,26,27}, together with alternative methods of rearing axenic flies, including serial transfer of axenic adults^18,27 or antibiotic treatment^13,18. Other dechorionation methods include ethanol washes and reduce^11,25,26 or extend⁸ hypochlorite treatment. Different wash steps may aid rearing different fly genotypes: in a previous study most of ~100 Drosophila genotypes were .......

Materials

Name	Company	Catalog Number	Comments
Brewer's Yeast	MP Biomedicals, LLC.	903312	http://www.mpbio.com/product.php?pid=02903312
Glucose	Sigma Aldrich	158968-3KG	http://www.sigmaaldrich.com/catalog/product/aldrich/158968?lang=en&region=US
Agar	Fisher--Lab Scientific	fly802010	https://www.fishersci.com/shop/products/drosophila-agar-8-100mesh-10kg/nc9349177
Welch's 100% Grape Juice Concentrate	Walmart or other grocery store	9116196	http://www.walmart.com/ip/Welch-s-Frozen-100-Grape-Juice-Concentrate-11.5-oz/10804406
Cage: 32 oz. Translucent Round Deli Container	Webstaurant Store	999L5032Y	http://www.webstaurantstore.com/newspring-delitainer-sd5032y-32-oz-translucent-round-deli-container-24-pack/999L5032Y.html
Translucent Round Deli Container Lid	Webstaurant Store	999YNL500	http://www.webstaurantstore.com/newspring-delitainer-ynl500-translucent-round-deli-container-lid-60-pack/999YNL500.html
Stock Bottles	Genesee Scientific	32-130	https://geneseesci.com/shop-online/product-details/?product=32-130
Droso-Plugs	Genesee Scientific	49-101	https://geneseesci.com/shop-online/product-details/?product=49-101
Nylon Mesh	Genesee Scientific	57-102	https://geneseesci.com/shop-online/product-details/715/?product=57-102
Plastic Bushing	Home Depot	100343125	http://www.homedepot.com/p/Halex-2-1-2-in-Rigid-Insulated-Plastic-Bushing-75225/100343125
Specimen Cup	MedSupply Partners	K01-207067	http://www.medsupplypartners.com/covidien-specimen-containers.html
Repeater M4	Eppendorf	4982000322	https://online-shop.eppendorf.us/US-en/Manual-Liquid-Handling-44563/Dispensers--Burettes-44566/Repeater-M4-PF-44619.html
50 ml Centrifuge Tubes	Laboratory Product Sales	TR2003	https://www.lpsinc.com/Catalog4.asp?catalog_nu=TR2003
Food Boxes	USA Scientific	2316-5001	http://www.usascientific.com/search.aspx?find=2316-5001
Lysing Matrix D Bulk	MP Biomedicals, LLC.	116540434	http://www.mpbio.com/search.php?q=6540-434&s=Search
Filter Pipette Tips, 300μl	USA Scientific	1120-9810	http://www.usascientific.com/search.aspx?find=1120-9810
Petri Dishes	Laboratory Product Sales	M089303	https://www.lpsinc.com/Catalog4.asp?catalog_nu=M089303
Ethanol	Decon Laboratories, INC.	2701	http://www.deconlabs.com/products.php?ID=88
Paintbrush	Walmart	5133	http://www.walmart.com/ip/Chenille-Kraft-5133-Acrylic-Handled-Brush-Set-Assorted-Sizes-colors-8-Brushes-set/41446005
Forceps	Fisher	08-882	https://www.fishersci.com/shop/products/fisherbrand-medium-pointed-forceps-3/p-128693
Household Bleach (6-8% Hypochlorite)	Walmart	550646751	http://www.walmart.com/ip/Clorox-Concentrated-Regular-Bleach-121-fl-oz/21618295
Universal Peptone	Genesee Scientific	20-260	https://geneseesci.com/shop-online/product-details/?product=20-260
Yeast Extract	Fisher Scientific	BP1422-500	https://www.fishersci.com/shop/products/fisher-bioreagents-microbiology-media-additives-yeast-extract-3/bp1422500?matchedCatNo=BP1422500
Dipotassium Phosphate	Sigma Aldrich	P3786-1KG	http://www.sigmaaldrich.com/catalog/search?term=P3786-1KG&interface=All&N=0&mode=match%20partialmax&lang=en&region=US&focus=product
Ammonium Citrate	Sigma Aldrich	25102-500g	http://www.sigmaaldrich.com/catalog/search?term=25102-500g&interface=All&N=0&mode=match%20partialmax&lang=en&region=US&focus=product
Sodium Acetate	VWR	97061-994	https://us.vwr.com/store/catalog/product.jsp?catalog_number=97061-994
Magnesium Sulfate	Fisher Scientific	M63-500	https://www.fishersci.com/shop/products/magnesium-sulfate-heptahydrate-crystalline-certified-acs-fisher-chemical-3/m63500?matchedCatNo=M63500
Manganese Sulfate	Sigma Aldrich	10034-96-5	http://www.sigmaaldrich.com/catalog/search?term=10034-96-5&interface=CAS%20No.&N=0&mode=match%20partialmax&lang=en&region=US&focus=product
MRS Powder	Sigma Aldrich	69966-500G	http://www.sigmaaldrich.com/catalog/product/sial/69966?lang=en&region=US
96 Well Plate Reader	BioTek (Epoch)	NA	http://www.biotek.com/products/microplate_detection/epoch_microplate_spectrophotometer.html
1.7 ml Centrifuge Tubes	USA Scientific	1615-5500	http://www.usascientific.com/search.aspx?find=1615-5500
Filter Pipette Tips, 1000μl	USA Scientific	1122-1830	http://www.usascientific.com/search.aspx?find=1122-1830
96 Well Plates	Greiner Bio-One	655101	https://shop.gbo.com/en/usa/articles/catalogue/article/0110_0040_0120_0010/13243/
Ceramic Beads	MP Biomedicals, LLC.	6540-434	http://www.mpbio.com/product.php?pid=116540434
Tissue Homogenizer	MP Biomedicals, LLC.	116004500	http://www.mpbio.com/product.php?pid=116004500
Class 1 BioSafety Cabinet	Thermo Scientific	Model 1395	http://www.thermoscientific.com/en/product/1300-series-class-ii-type-a2-biological-safety-cabinet-packages.html