Effects of heat-assisted sample desiccation on microbiome surveys

Sample preservation remains a challenge in microbiome surveys, particularly in remote areas. Drying samples eliminates the need for cold chains and preservatives, but sophisticated desiccation tools such as lyophilization are impractical in the field. Further, the effects of sample drying on modern analyses, such as gene-centric metagenomics and metagenome-assembled genome (MAG) recovery, remain poorly understood. Here we explore heat-assisted sample desiccation followed by storage at room temperature as a cost-effective and practical solution in the field. We assess its effects relative to freezing on typical metagenomic and 16 S rRNA amplicon sequence analyses of bacterial and archaeal communities, using 60 samples from 6 different source materials (soils from 3 locations, feces from 3 animals). We consider multiple metrics related to the success of DNA extraction, sequencing, contig assembly, OTU clustering, gene annotation and MAG recovery, as well as impacts on inferred microbial community composition. We find that, while desiccation had a significant negative impact on multiple metrics related to DNA extraction success, its impacts on downstream metrics such as OTU richness, Shannon diversity, gene annotation and MAG recovery were more nuanced and often insignificant. Further, while the preservation method had a significant influence on the inferred microbial community composition, samples from different source materials (e.g., soils from different locations, or feces from different individuals) remained clearly distinguishable. We conclude that heat-assisted desiccation can be a viable sample preservation method for microbiome studies, when a high consistency with frozen samples is not a requirement.