Prokaryotic genome size and SSU rDNA copy number: Estimation of microbial relative abundance from a mixed population

Determination of the relative abundance of a specific prokaryote in an envi ronmental sample is of major interest in applied and environmental microbio logy. Relative abundance can be calculated using knowledge of SSU rDNA copy number, amount of SSU rDNA in the sample, and a weighted average estimate of the genome sizes for organisms in the original sample. By surveying the literature, we provide estimates of genome size and SSU rDNA copy number fo r 303 and 101 prokaryotes, respectively. This compilation can be used to ma ke reasonable estimates for a wide range of organisms in the calculation of relative abundance. A statistical analysis suggests that no correlation ex ists between genome size and SSU rDNA copy number. A phylogenetic analysis is used to offer insights into the evolution of both genome size and SSU rD NA copy number.