Industry Symposia

Title:

The Bias Before the Sequencer: How Fixed-Cycle Amplification Distorts Microbial Community Profiles

Abstract:

Amplification influences most quality metrics in amplicon-based microbiome studies. Yet most library preparations still use a fixed cycle number for every sample, regardless of input amount, community complexity, or inhibitors. Low-input samples are under-amplified while high-input samples are over-cycled, generating chimeras, odd-size products, uneven read depth, and loss of rare taxa. Bioinformatic filtering can remove some artifacts, but it cannot restore molecules that were never correctly represented. The opportunity for artifacts grows with amplicon length, especially with full-length 16S rRNA gene sequencing.

With adaptive amplification, each well is cycled independently, monitored by real-time fluorescence, and stopped once it reaches a target yield, normalizing libraries during PCR. We summarize matched comparisons against fixed-cycle PCR across short-read and PacBio full-length 16S workflows. In one 16S assay, the mean chimera rate fell from 39.7% to 9.2%, and from 5.6% to 3.2% in a second, with all 86 matched samples showing qualitative improvement.  The share of pooled libraries in the expected size range rose from 9–19% to 74–78%. In a PacBio full-length 16S study, adaptive cycling retained more processed reads (10.5M) than 20-, 24-, or 30-cycle protocols (6.7–9.2M). High-diversity specimens were the most vulnerable to read loss at high cycle numbers. Adaptive amplification also improved alpha-diversity estimates and removed separate quantification and normalization steps from the workflow.

The benefit is largest where reactions differ: wide or unknown input ranges, long amplicons, complex communities such as soil, and tight pooling or read budgets. The goal is not more amplification, but the right amplification for each sample.

Presenter:

Tushar Shah, Business Development at n6