Comparison of Environmental and Culture-Derived Bacterial Communities through 16S Metabarcoding: A Powerful Tool to Assess Media Selectivity and Detect Rare Taxa.

To compare environmental and culture-derived microbial communities, we performed 16S metabarcoding of uncultured samples and their culture-derived bacterial lawns. Microbial communities were obtained from freshwater river samples representative of an anthropization gradient along a river stream. Their culture-derived bacterial lawns were obtained by growing aliquots of the samples on a broad range medium and on two different semi-selective media. The V3-V4 16S rRNA region was amplified and sequenced. The bacterial diversity of water samples decreased from the upper to lower stream sampling sites and, as expected, these differences were mostly suppressed by the culture step. Overall, the diversity of cultured-derived bacterial communities reflected selectivity of each tested medium. Comparison of treatments indicated that the culture selected both detected and rare undetected environmental species. Accurate detection of rare environmental bacteria of the genus by 16S metabarcoding of the culture lawn was demonstrated. Interestingly, for abundant taxa, such as those of the genus, the culture/environment ratio varied between sampled sites, indicating the difficulty of comparing cultured-derived taxa abundance between environmental sites. Finally, our study also highlighted media specificity and complementarity: bacterial communities grown on the two selective media, while selecting a small set of specific species, were mostly a subset of the bacterial community observed on the broad range medium.