Résumé
Housekeeping genes have proven to be effective taxonomic markers for characterizing bacterial microbiota in short-read amplicon metabarcoding studies. A region of the rpoB gene has been shown to minimize Operational Taxonomic Unit (OTU) overestimation bias with a high degree of accuracy, providing better species-level taxonomic resolution (J.-C. Ogier, S. Pagès, M. Galan, M. Barret, and S. Gaudriault, S., BMC Microbiol. 19:171, https://doi.org/10.1186/s12866-019-1546-z). However, the primers for rpoB are highly degenerate, leading to potential problems in the amplification of bacterial DNA present at low concentration in the sample or embedded within eukaryotic matrices, as for the host-associated microbiota. We addressed these limitations by using a two-step PCR approach to optimize the rpoB procedure. The first PCR amplifies a region of the rpoB gene with the outer primers, and the second PCR then uses primers incorporating Illumina adapters, the inner primers, to amplify the taxonomic marker for metabarcoding. We first used in silico approaches to evaluate the universality of the outer and inner rpoB primers. We then tested the nested rpoB PCR method on commercial mock samples. The nested PCR approach increased amplification efficiency for dilute samples without biasing the bacterial composition of the mock sample revealed by metabarcoding relative to single-step PCR. We also tested the nested rpoB PCR method on field-collected samples of insects. The nested PCR outperformed single-step PCR, increasing amplification efficiency for bacterial DNA present at low concentrations (insect oral secretions) or embedded in eukaryotic DNA matrices (insect larvae). This method provides a promising new strategy for characterizing host-associated microbiota.