Metatranscriptomics of cheese microbial communities: Efficiency of RNA extraction from various cheese types and of mRNA enrichment

Microbial communities from cheeses contribute to the development of typical organoleptic properties. Metatranscriptomic analyses can be used to provide a global picture of the functioning of these communities. Our objective was to evaluate the efficiency of RNA extraction from various cheese types and to evaluate mRNA enrichment procedures for metatranscriptomic analyses. For the 32 tested cheese brands, corresponding to five cheese types, the extraction yield varied from 1 μg to 363 μg RNA per gram of cheese and, overall, the yield was lower for fresh cheeses and for the core of pressed cooked cheeses than for the other cheese types. Pressed cooked cheeses also had a lower RNA integrity than the other cheese types. For total RNA extracts from four cheeses, approximately 99% of the sequencing reads corresponded to ribosomal RNA, and mRNA enrichment by RiboPOOL and FastSelect kits decreased this percentage to a range of 75 to 97% and of 53 to 76%, respectively. Comparison of RNA libraries after mRNA enrichment with libraries of undepleted total RNA showed that the FastSelect mRNA enrichment had a lower impact on the gene expression profiles of five target cheese species than the riboPOOL kit and the oligo (dT) selection method. The procedures that we describe in the present study may be useful for metatranscriptomic analysis of various cheese types.