Effects of Vacuum-Heat-Assisted Sample Desiccation on Microbiome Surveys

Sample preservation in the field and during transport can be a logistical challenge for microbiome surveys, particularly in remote areas. Sample desiccation eliminates the need for complicated cold chains and dangerous preservatives. However, the effects of desiccation on modern microbiome workflows such as gene-centric metagenomic profiling and metagenome-assembled genome (MAG) binning, remain poorly understood. In addition, most common desiccation tools such as lyophilisation cannot easily be deployed in the field. Here, we describe a proof-of-principle sample desiccator using vacuum and heat, specifically built for deployment in the field and exhibiting low power consumption and cost. We then test the effects of vacuum-heat-assisted sample desiccation followed by storage at room temperature, in comparison to conventional freezing, on multiple soil and animal faecal samples, via metagenomic and 16S rRNA amplicon sequencing. We consider multiple metrics related to the success of DNA extraction, sequencing, contig assembly, OTU clustering, gene annotation and MAG construction, as well as effects on inferred microbial community composition. We find that the impact of drying on considered success metrics was almost always either minor, non-significant or positive. For a subset of source materials we observed moderate but statistically significant differences in terms of inferred microbial taxonomic and genetic composition. We conclude that vacuum- and heat-assisted desiccation can be a useful, practical and cost-effective tool for microbiome field surveys, when a high consistency with frozen samples is not required.