GC Fractionation Allows Comparative Total Microbial Community Analysis, Enhances Diversity Assessment, and Facilitates Detection of Minority Populations of Bacteria

A major challenge in modern microbial ecology is to effectively and accurately determine total microbial community diversity, particularly with regard to the detection of (a) unculturable and fastidious bacterial species and (b) those present only in low abundance (i.e., minority populations). A common theme in published studies and textbooks regarding microbial community diversity in most environments is that typically only 0.1–1.0% of bacteria observed by direct microscopic enumeration can be recovered on using general laboratory media (e.g., see Ferguson, et al. [1984], Fliermans and Balkwill [1989], Hazen et al. [1991], RappeI and Giovannoni [2003], Janssen [2006], Jones et al. [2009], and Spain et al. [2009]). As a result, many microbial ecologists are of the opinion that the vast majority of microbial diversity remains uncharacterized, highlighting both potentially huge gaps in our understanding of how microbial communities function in an ecosystem and the large reservoir of possibly useful organisms and genes. This concern has spurred the development of a large number of molecular approaches for microbial community analysis, many of which are based on analysis of nucleic acids extracted directly from environmental samples to enhance our