Use of internal standards for quantitative metatranscriptome and metagenome analysis.

Next generation sequencing-enabled metatranscriptomic and metagenomic datasets are providing unprecedented insights into the functional diversity of microbial communities, allowing detection of the genes present in a community as well as differentiation of those being actively transcribed. An emerging challenge of meta-omics approaches is how to quantitatively compare metagenomes and metatranscriptomes collected across spatial and temporal scales, or among treatments in experimental manipulations. Here, we describe the use of internal DNA and mRNA standards in meta-omics methodologies, and highlight how data collected in an absolute framework (per L or per cell) provides increased comparative power and insight into underlying causes of differences between samples.