Direct Profiling of Environmental Microbial Populations by Thermal Dissociation Analysis of Native rRNAs Hybridized to

Oligonucleotide microarrays were used to profile directly extracted rRNA from environmental microbial populations without PCR amplification. In our initial inspection of two distinct estuarine study sites, the hybridization patterns were reproducible and varied between estuarine sediments of differing salinities. The determination of a thermal dissociation curve (i.e., melting profile) for each probe-target duplex provided information on hybridization specificity, which is essential for confirming adequate discrimination between target and nontarget sequences. The vast and previously unrecognized diversity of the micro-bial world discovered during the last decade reflects the rapid progress made in the development of molecular techniques for direct characterization of environmental systems. Among tech-niques now commonly employed, recovery of 16S rRNA se-quences by using standard methods of PCR amplification, cloning, and sequencing has provided the most encompassing perspectives of microbial diversity (8). However, such descrip-tions of diversity have been accompanied by modest progres