DNA stable-isotope probing is a cultivation-independent method to identify and characterize active communities of microorganisms that are capable of utilizing specific substrates. Assimilation of substrate enriched in heavy isotope leads to incorporation of labelled atoms into microbial biomass. Density gradient ultracentrifugation retrieves labelled DNA for downstream molecular analyses.
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In This Article
Summary
Abstract
DNA stable-isotope probing (DNA-SIP) is a powerful technique for identifying active microorganisms that assimilate particular carbon substrates and nutrients into cellular biomass. As such, this cultivation-independent technique has been an important methodology for assigning metabolic function to the diverse communities inhabiting a wide range of terrestrial and aquatic environments. Following the incubation of an environmental sample with stable-isotope labelled compounds, extracted nucleic acid is subjected to density gradient ultracentrifugation and subsequent gradient fractionation to separate nucleic acids of differing densities. Purification of DNA from cesium chloride retrieves labelled and unlabelled DNA for subsequent molecular characterization (e.g. fingerprinting, microarrays, clone libraries, metagenomics). This JoVE video protocol provides visual step-by-step explanations of the protocol for density gradient ultracentrifugation, gradient fractionation and recovery of labelled DNA. The protocol also includes sample SIP data and highlights important tips and cautions that must be considered to ensure a successful DNA-SIP analysis.
Protocol
1. Preparation of Reagents
DNA-SIP requires the use of reagents that should be prepared in advance of the actual procedure. The directions for preparing each reagent are listed in this section and are modified from a previous SIP protocol1.
- Cesium chloride (CsCl) solution for preparing SIP gradients - Prepare a 7.163 M CsCl solution by gradually dissolving 603.0 g of CsCl in distilled and deionized water (ddH2O) to a final volume of 500 mL. Be careful not to exceed 500 mL! Warming the solution slightly while stirring will help dissolve all of the CsCl. Aliquot the final solution in sealed aliquots. I....
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Discussion
Proper design of stable-isotope probing experiments is of critical importance for obtaining labelled DNA above the background unlabelled community. Considerations related to sample incubation times, substrate concentrations, incubation conditions (e.g. nutrients, soil moisture content), cross-feeding and replication have been discussed elsewhere 10,18 and we recommend the reader consult these publications when designing a SIP incubation. Related to the current protocol, it is worth commenting on additional con.......
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Disclosures
No conflicts of interest declared.
Acknowledgements
This work was supported by Strategic Project and Discovery Grants to J.D.N. from the Natural Sciences and Engineering Research Council of Canada (NSERC).
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Materials
| Name | Company | Catalog Number | Comments | |
|---|---|---|---|---|
| Bromophenol Blue | Reagent | Fisher Scientific | BP115-25 | |
| Cesium chloride | Reagent | Fisher Scientific | BP210-500 | |
| Ethanol, reagent grade | Reagent | Sigma-Aldrich | 652261 | |
| Ethidium bromide | Reagent | Sigma-Aldrich | E1510 | |
| Hydrochloric acid | Reagent | Fisher Scientific | 351285212 | |
| Linear polyacrylamide | Reagent | Applichem | A6587 | |
| Polyethylene Glycol 6000 | Reagent | VWR international | CAPX1286L-4 | |
| Potassium Chloride | Reagent | Fisher Scientific | AC42409-0010 | |
| Sodium Chloride | Reagent | Fisher Scientific | S2711 | |
| Sodium Hydroxide pellets | Reagent | Fisher Scientific | S3181 | |
| Tris base | Reagent | Fisher Scientific | BP1521 | |
| Dark Reader | Equipment | Clare Chemical | DR46B | |
| Microcentrifuge | Equipment | Eppendorf | 5424 000.410 | |
| Nanodrop 2000 | Equipment | Fisher Scientific | 361013650 | |
| Infusion pump | Equipment | Braintree Scientific, Inc. | N/A | Model Number: BSP See www.braintreesci.com for ordering details. |
| Tube sealer | Equipment | Beckman Coulter Inc. | 358312 | |
| Ultracentrifuge | Equipment | Beckman Coulter Inc. | ||
| Ultracentrifuge rotor | Equipment | Beckman Coulter Inc. | 362754 | |
| Ultraviolet light source | Equipment | UVP Inc. | 95-0017-09 | Any UV source will suffice |
| Ultraviolet light face shield | Equipment | Fisher Scientific | 114051C | |
| Butyl rubber stoppers, gray | Material | Sigma-Aldrich | 27232 | |
| Centrifuge tubes | Material | Beckman Coulter Inc. | 342412 | |
| Hypodermic needle, 23 gauge, 2” length | Material | BD Biosciences | 305145 | |
| Microfuge tubes, 1.5 mL | Material | DiaMed | AD151-N500 | |
| Open center seals, 20 mm diameter | Material | Sigma-Aldrich | 27230-U | |
| Pasteur pipettes, glass | Material | Fisher Scientific | 13-678-6C | |
| Pipet tips | Material | DiaMed | BPS340-1000 | Catalogue number is for 200 μl tips. 10 or 20 μl tips may be purchased from the same source |
| Pump tubing 1.5 mm bore x 1.5 mm wall | Material | Appleton Woods | ||
| Screw-cap tubes, 15 mL | Material | DiaMed | AD15MLP-S | |
| Serum vials, 125 mL volume | Material | Sigma-Aldrich | Z114014 | |
| Syringe, 60 mL | Material | BD Biosciences | 309653 |
References
- Neufeld, J. D. DNA stable-isotope probing. Nat. Protocols. 2, 860-866 (2007).
- Neufeld, J. D., Boden, R., Moussard, H., Schäfer, H., Murrell, J. C. Substrate-specific clades of active marine methylotrophs associated with a phytoplankton bloom in a t....
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