Taxon appearance from extraction and amplification steps demonstrates the value of multiple controls in tick microbiome analysis

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anglais. The developmentof high throughput sequencing (HTS) technologies has substantially improvedanalysis of bacterial community diversity, composition,and functions. Over the last decade, HTS has been used extensively to identify the diversity and composition of tick microbial communities. However, a growing number of studies are warning about the impact of contamination brought along the different steps of the analytical process, from DNA extraction to amplification. In low biomass samples, e.g. individual tick samples, these contaminants may represent a large part of the obtained sequences,and thus generate considerable errors in downstream analyses and in the interpretation of results. Most studies of tick microbiota either do not mention the inclusion of controls during the DNA extraction or amplification steps, or consider the lack of an electrophoresis signal as an absence of contamination. In this context, we aimed to assess theproportion of contaminantsequences resulting from thesesteps. We analyzed the microbiota of individual Ixodesricinusticksbyincluding several categories of controls throughout the analytical process:crushing, DNA extraction,and DNA amplification Results Controls yielded a significant number of sequences (1,126 to 13,198 mean sequences,depending onthe control category). Some operational taxonomic units (OTUs)detected in these controls belong to genera reported in previous tick microbiota studies. Inthis study, these OTUs accounted for 50.9% of the total number of sequences inour samples, and wereconsidered contaminants. Contamination levels (i.e. the percentage of sequences belonging to OTUs identified as contaminants) variedwith tick stage and gender: 76.3% of nymphs and 75% of males demonstrated contamination over 50%, while most females (65.7%) had rateslower than 20%. Contamination mainly correspondedto OTUs detected in crushing and DNA extraction controls, highlighting the importance of carefully controlling these steps. -Conclusion Here,we showed that contaminant OTUs from extraction and amplification stepscan represent more than half the total sequence yield in sequencing runs,and lead to unreliable results when characterizing tick microbial communities.We thus strongly advise the routine use of blanks and negative controls in tick microbiota studies, and more generally in studies involving low biomass.