11When studying the microbiome using next generation sequencing, DNA extraction method, 12 sequencing procedures and bioinformatic processing are crucial to obtain reliable data. 13 Method choice has been demonstrated to strongly affect the final biological interpretation. 14 We assessed the performance of three DNA extraction methods and two bioinformatic 15 pipelines for bacterial microbiota profiling through 16S rRNA gene amplicon sequencing, 16 using positive and negative controls for DNA extraction and sequencing, and eight different 17 types of high-or low-biomass samples. Performance was evaluated based on quality control 18 passing, DNA yield, richness, diversity and compositional profiles. All DNA extraction 19 methods retrieved the theoretical relative bacterial abundance with maximum three-fold 20 change, although differences were seen between methods, and library preparation and 21 sequencing induced little variation. Bioinformatic pipelines showed different results for 22 estimating richness, but diversity and compositional profiles were comparable. DNA 23 extraction methods were successful for feces and oral swabs and variation induced by DNA 24 extraction methods was lower than inter-subject (biological) variation. For low-biomass 25 samples, a mixture of genera present in negative controls and sample-specific genera, 26possibly representing biological signal, were observed. We conclude that the tested 27 bioinformatic pipelines perform equally with pipeline-specific advantages and disadvantages.
28Two out of three extraction methods performed equally well, while one method was less 29 accurate regarding retrieval of compositional profiles. Lastly, we demonstrate the importance 30 of including negative controls when analyzing low bacterial biomass samples.
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IMPORTANCE 32Method choice throughout the workflow of a microbiome study, from sample collection to 33 DNA extraction and sequencing procedures, can greatly affect results. This study evaluated 34 3 three different DNA extraction methods and two bioinformatic pipelines by including 35 positive and negative controls, and various biological specimens. By identifying an optimal 36 combination of DNA extraction method and bioinformatic pipeline use, we hope to 37 contribute to increased methodological consistency in microbiome studies. Our methods were 38 not only applied to commonly studied samples for microbiota analysis, e.g. feces, but also for 39 more rarely studied, low-biomass samples. Microbiota composition profiles of low-biomass 40 samples (e.g. urine and tumor biopsies) were not always distinguishable from negative 41 controls, or showed partial overlap, confirming the importance of including negative controls 42 in microbiome studies, especially when low bacterial biomass is expected. 43