Abstract
Metagenomic libraries archive large fragments of contiguous genomic sequences from microorganisms without requiring prior cultivation. Generating a streamlined procedure for creating and screening metagenomic libraries is therefore useful for efficient high-throughput investigations into the genetic and metabolic properties of uncultured microbial assemblages. Here, key protocols are presented on video, which we propose is the most useful format for accurately describing a long process that alternately depends on robotic instrumentation and (human) manual interventions. First, we employed robotics to spot library clones onto high-density macroarray membranes, each of which can contain duplicate colonies from twenty-four 384-well library plates. Automation is essential for this procedure not only for accuracy and speed, but also due to the miniaturization of scale required to fit the large number of library clones into highly dense spatial arrangements. Once generated, we next demonstrated how the macroarray membranes can be screened for genes of interest using modified versions of standard protocols for probe labeling, membrane hybridization, and signal detection. We complemented the visual demonstration of these procedures with detailed written descriptions of the steps involved and the materials required, all of which are available online alongside the video.
Protocol
Discussion
The stripping procedure has not been optimized. However, the stripping procedure given in the manufacturer’s instruction (2 washes each, 10 min in 100% ethanol, 1 wash of 1 h at 60°C in 0.5% SDS) is insufficient. At least overnight incubation in 100% ethanol is necessary to dissolve the ECF reaction product; several days incubation in 100% ethanol appears to have no adverse effects on the ability to reprobe the membrane. The manufacturer’s SDS treatment also appears to be insufficient. NUF has tried 1 h at 80°C w…
Materials
| Material Name | Type | Company | Catalogue Number | Comment |
|---|---|---|---|---|
| AlkPhos Direct Labelling Reagents | kit | Amersham | RPN3680 | Contains labeling reagent, cross-linker solution, reaction buffer, water, control DNA, hybridization buffer, blocking reagent. Store hybridization buffer and blocking reagent at room temperature, other reagents at 2-8°C. |
| ECF Substrate | kit | Amersham | RPN3685 | Contains ECF substrate, ECF substrate dilution buffer. Note: Pack contains total 60 ml reagent; aliquot into 10 ml samples in Falcon tube and store at 20°C. Use about 10 ml per membrane (size of 22 by 22 cm). |
| 20x Secondary Wash Buffer | buffer | 121 g Tris (final 1 M), 117 g NaCl (final 2 M). Adjust pH to 10. Adjust to 1 L with water. Store at 2-8°C for up to 4 months. | ||
| 0.5 M NaH2PO4 buffer pH 7 | buffer | 69 g NaH2PO4.H2O. Adjust pH to 7 with NaOH. Adjust to 1 L with water. Store at room temperature. | ||
| 1 M MgCl2 | 50.8 g MgCl2.6H2O Adjust to 250 ml with water. Store at room temperature. | |||
| 10% (w/v) SDS | 20 g SDS Adjust to 200 ml with water. Store at room temperatur |
