show Abstracthide AbstractDNA extraction plays a crucial role in determining the variability of results obtained through 16S rRNA amplicon sequencing. This variability poses a challenge when attempting to compare findings obtained using different methods. In particular, samples rich in clay, such as bentonite commonly employed as backfill material in engineered barriers for nuclear waste disposal, can impede the efficiency of various standard cultivation-independent techniques. Furthermore, these samples often contain low biomass, further complicating the extraction process. To address these concerns, we conducted an inter-laboratory comparison study to thoroughly assess the efficacy of two published DNA extraction methods specifically designed for bentonite samples.