Phylogenetic analysis of the bacterial communities in marine sediments

For the phylogenetic analysis of microbial communities present in environmental samples microbial DNA can be extracted from the sample, 16S rDNA can be amplified with suitable primers and the PCR, and clonal libraries can be constructed. We report a protocol that can be used for efficient cell lysis and recovery of DNA from marine sediments. Key steps in this procedure include the use of a bead mill homogenizer for matrix disruption and uniform cell lysis and then purification of the released DNA by agarose gel electrophoresis. For sediments collected from two sites in Puget Sound, over 96% of the cells present were lysed. Our method yields high-molecular-weight DNA that is suitable for molecular studies, including amplification of 16S rRNA genes. The DNA yield was 47 mu g per g (dry weight) for sediments collected from creosote-contaminated Eagle Harbor, Wash. Primers were selected for the PCR amplification of (eu)bacterial 16S rDNA that contained linkers with unique 8-base restriction sites for directional cloning. Examination of 22 16S rDNA clones showed that the surficial sediments in Eagle Harbor contained a phylogenetically diverse population of organisms from the Bacteria domain (G. J. Olsen, C. R. Woese, and R. Overbeek, J. Bacteriol. 176:1-6, 1994) with members of six major lineages represented: alpha, delta, and gamma Proteobacteria; the gram-positive high G+C content subdivision; clostridia and related organisms; and planctomyces and related organisms. None of the clones were identical to any representatives in the Ribosomal Database Project small subunit RNA database. The analysis of clonal representatives is the first report using molecular techniques to determine the phylogenetic composition of the (eu)bacterial community present in coastal marine sediments.