Micelle PCR amplification
The micPCR consisted of two PCR rounds of micPCR amplification. This was necessary, because micPCR only yields a limited number of amplicons per template molecule, which is a consequence of the limited reaction volume contained in a single micelle. We estimated that after a micPCR only 1E + 04 amplicon molecules were formed in a single micelle starting with a single genomic DNA fragment carrying a 16S rRNA gene copy. This low number of amplicon molecules is not sufficient for NGS of samples containing low amounts of bacterial DNA, such as nose swabs. However, using a second round of micPCR allowed us to increase the number of amplicon molecules for NGS, as well as allowing the addition of Molecular Identification sequences (MID) and Roche 454 specific A and B sequences. In the first step, micPCR was performed using modified 357F and 926R primers that amplified the V3–V5 regions of 16S rRNA genes and which incorporated universal sequence tails at their 5′ ends. In the second step, a micPCR was again used, but to amplify micPCR amplicons obtained from the first step micPCR. The second step micPCR utilized primers containing complementary sequences to the universal tails and included additional 454 sequencing-specific nucleotides, and specimen-specific MIDs. For both amplification steps, water-in-oil emulsions were prepared using the Micellula DNA Emulsion Kit (Roboklon). The oil phase comprised ~73% Emulsion component 1, ~7% Emulsion component 2, and 20% Emulsion component 3, which was mixed for 5 minutes in a cold room as described by the manufacturer. The aqueous phase was a PCR reaction mix comprising 0.01 mg/ml BSA, 2 μM of each primer, 200 μM dNTP mix, and 2.5 U Taq polymerase with 1× PCR Buffer B (EURx). Template DNA and water were added to give a final volume of 50 μL for each sample. Water-in-oil emulsions were prepared by adding 50 μL of pre-cooled PCR reaction mix to 300 μL of pre-cooled oil phase. The first round of micPCR was carried out using the following cycling conditions: 95 °C for 2 minutes followed by 25 cycles of PCR, with cycling conditions of 15 seconds at 95 °C, 30 seconds at 55 °C, and 60 seconds at 72 °C, and a final extension at 72 °C for 7 minutes. Emulsions were broken by the addition of 1 mL 2-butanol, and 400 μL of Orange-DX buffer (Roboklon) was added to the broken emulsion solution. This solution was centrifuged for phase separation. For the purification of DNA within the water phase, NucliSENS EasyMAG reagents (Biomérieux) were used according to the manufacturer’s instructions. To normalize DNA concentration and reduce the number of template molecules for the second round of amplification, the purified DNA was diluted 1E + 04 or 1E + 02-fold for high and low inputs, respectively, during the first micPCR. The second round of micPCR was performed under the following conditions: initial denaturation at 95 °C for 2 minutes followed by 25 cycles of PCR, with cycling conditions of 15 seconds at 95 °C, 30 seconds at 50 °C and 60 seconds at 72 °C. During the first 10 cycles of PCR, the annealing temperature was increased by 0.5 °C per cycle to an annealing temperature of 55 °C. The PCR was stopped after a final extension at 72 °C for 7 minutes. Again, emulsions were broken using 2-butanol, and DNA was purified using NucliSENS EasyMAG reagents (Biomérieux).
ขยาย micelle PCRThe micPCR consisted of two PCR rounds of micPCR amplification. This was necessary, because micPCR only yields a limited number of amplicons per template molecule, which is a consequence of the limited reaction volume contained in a single micelle. We estimated that after a micPCR only 1E + 04 amplicon molecules were formed in a single micelle starting with a single genomic DNA fragment carrying a 16S rRNA gene copy. This low number of amplicon molecules is not sufficient for NGS of samples containing low amounts of bacterial DNA, such as nose swabs. However, using a second round of micPCR allowed us to increase the number of amplicon molecules for NGS, as well as allowing the addition of Molecular Identification sequences (MID) and Roche 454 specific A and B sequences. In the first step, micPCR was performed using modified 357F and 926R primers that amplified the V3–V5 regions of 16S rRNA genes and which incorporated universal sequence tails at their 5′ ends. In the second step, a micPCR was again used, but to amplify micPCR amplicons obtained from the first step micPCR. The second step micPCR utilized primers containing complementary sequences to the universal tails and included additional 454 sequencing-specific nucleotides, and specimen-specific MIDs. For both amplification steps, water-in-oil emulsions were prepared using the Micellula DNA Emulsion Kit (Roboklon). The oil phase comprised ~73% Emulsion component 1, ~7% Emulsion component 2, and 20% Emulsion component 3, which was mixed for 5 minutes in a cold room as described by the manufacturer. The aqueous phase was a PCR reaction mix comprising 0.01 mg/ml BSA, 2 μM of each primer, 200 μM dNTP mix, and 2.5 U Taq polymerase with 1× PCR Buffer B (EURx). Template DNA and water were added to give a final volume of 50 μL for each sample. Water-in-oil emulsions were prepared by adding 50 μL of pre-cooled PCR reaction mix to 300 μL of pre-cooled oil phase. The first round of micPCR was carried out using the following cycling conditions: 95 °C for 2 minutes followed by 25 cycles of PCR, with cycling conditions of 15 seconds at 95 °C, 30 seconds at 55 °C, and 60 seconds at 72 °C, and a final extension at 72 °C for 7 minutes. Emulsions were broken by the addition of 1 mL 2-butanol, and 400 μL of Orange-DX buffer (Roboklon) was added to the broken emulsion solution. This solution was centrifuged for phase separation. For the purification of DNA within the water phase, NucliSENS EasyMAG reagents (Biomérieux) were used according to the manufacturer’s instructions. To normalize DNA concentration and reduce the number of template molecules for the second round of amplification, the purified DNA was diluted 1E + 04 or 1E + 02-fold for high and low inputs, respectively, during the first micPCR. The second round of micPCR was performed under the following conditions: initial denaturation at 95 °C for 2 minutes followed by 25 cycles of PCR, with cycling conditions of 15 seconds at 95 °C, 30 seconds at 50 °C and 60 seconds at 72 °C. During the first 10 cycles of PCR, the annealing temperature was increased by 0.5 °C per cycle to an annealing temperature of 55 °C. The PCR was stopped after a final extension at 72 °C for 7 minutes. Again, emulsions were broken using 2-butanol, and DNA was purified using NucliSENS EasyMAG reagents (Biomérieux).
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